Introducing Common Migrant Moths (part 2) - the next eight

Small Mottled Willow (above) has probably been Britain's most ubiquitous migrant moth this year. The arrival of 19 more in my trap over the past couple of days has prompted me to post the second part of this blog on our common migrant species. 

Part 1 (link here) looked at the seven commonest immigrants - the ones that UK moth recorders are most likely to encounter. The present post considers the next group of eight species that sit in that 'grey zone' between rare and common, although what that means in practice will depend on where you are trapping. Moth recorders on Britain's south and east coasts will generally get better numbers than those inland, but even down here in Dorset I am very happy when any of these species turn up.

The eight moths covered in this post all had 3,000+ British and Irish records between 2010 and 2019, taken from the Atropos website. This is compiled by Sean Clancy, who does a great (and unenviable) job keeping on top of the data using information from county moth recorders. Obviously, these numbers will now be out of date - this year's Small Mottled Willow influx may well move that species into the 'very common' bracket - but still give useful pointers towards what's common and what's not.

Top of this group of eight is the Vestal (below), with 15,405 records from 2010 to 2019.

Vestal Rhodometra sacraria - Dorset 22.9.19

This is a lovely moth. Linnaeus named it sacraria (from 'holy' or 'sacred') either because its colours reminded him of priestly robes or its simple yet beautiful pattern suggested virtue or chastity. The early collectors who named it the Vestal were clearly thinking of the latter, which is both odd and yet typical of the whimsical nature of our common moth names. (Maintaining a chaste and virtuous existence will of course be the last thing on a moth's mind.)

Identification is straightforward. While the colours can vary (see below), the basic pattern never changes. When resting, the moth has an upright, tent-like posture that differs from many of the other members of its family (the Geometridae) that spread their wings flat or hold them together vertically.

Globally, the Vestal is a widespread species, occurring in Europe, Asia, Africa and South America. Early arrivals can breed in Britain, with 'home grown' second generation individuals adding to summer and autumn migrants. But there is little evidence of that they can successfully overwinter here. 

An interesting feature of the Vestal is that its colour depends on the temperature experienced by the growing caterpillar. The 'classic' look of a strong pink stripe across a light straw-coloured background (as in the above photo) suggests that the caterpillar lived through high temperatures, so this moth was probably an arrival from southern Europe. Duller colours indicate that its origin may have been further north. The darker example pictured below, an autumn arrival, may well have bred in England.

Vestal Rhodometra sacraria (darker example) - Dorset 27.10.22

Britain's migrant moth of the moment, the Small Mottled Willow, comes second on the list with 8,248 records 2010-2019, but the annual average is now surely higher. This species is well known for its irregular habits - it's either feast or famine, with large numbers arriving in some years while other years see hardly any. I trapped only 13 last year (2025), while my 2026 total to date is 228! 

Small Mottled Willow Spodoptera exigua - Dorset 12.6.25

At first sight, Small Mottled Willow is a rather non-descript member of the noctuid family. However, despite a wide variation in size (which we have certainly seen this year), they are easy to identify once you get your eye in. The pinky-orange oval and kidney mark are good clues, but it is the moth's posture that is the real give-away. When at rest, its wings are held in a similarly tent-like manner to the Vestal, and often partly rolled under the body, giving a generally narrow appearance. Pale Mottled Willow is perhaps the most likely confusion species, but that has wider wings that are held flat when at rest. 

Known also as Beet Armyworm, Small Mottled Willow is found from North America to Australia, and causes significant damage to crops in tropical and semi-tropical lands. Its capacity to trouble farmers in Britain is severely limited by its inability to survive the colder winters here. For the time being.

Third on our list is Scarce Bordered Straw, with 7,071 records 2010-2019. Given that this moth is more likely to be seen here than its close namesake the Bordered Straw (see later), its name is rather unhelpful - which applies to a number of other British moths, as it happens.

Scarce Bordered Straw Helicoverpa armigera - Dorset 1.9.24

Scare Bordered Straw is one of the more tricky moths to identify because it lacks any one obvious distinguishing feature. The fact that it's a variable species doesn't help. At first sight, it is a classic member of the noctuid family (see my blog on moth family ID here), with a chunky, rather thickset appearance and a flat resting position. Consistent features are the oval and kidney marks which have fine dark outlines and central spots. Also look out for the wavy black cross-lines and the dark outer band (at the bottom of my photos). Here is a more red-brown coloured individual:

Scarce Bordered Straw Helicoverpa armigera (reddish-brown colour) - Dorset 27.10.22 

Also called Old World Bollworm, Scarce Bordered Straw is a major agricultural pest in tropical and subtropical regions of Africa, Asia and Australia, as well as being found across much of Europe. Its caterpillars are however rarely seen in Britain.

Sticking with the noctuid family, our fourth species is the Pearly Underwing (below), with 5,663 records 2010-2019. Known also as the Variegated Cutworm, and is found in North and South America and East Asia as well as Southern Europe. As with the previous two species, it is an agricultural pest in warmer climates.

Pearly Underwing Peridroma saucia - Dorset 17.6.26

Like Scarce Bordered Straw, Pearly Underwing seems at first glance to be a rather undistinguished moth. But although its pattern and colouration are variable, there are several distinctive features. First, it is a large moth, its size range overlapping with that of the familiar Large Yellow Underwing. Second, as the name suggests, its hindwings have a pearl-like translucence, although this is set against dark veins and a dark band around the edge - and getting the moth to show you can be a bit of a challenge. Don't expect to see a shining white hindwing. But the best identification character of all requires you to look at the moth from the side, which reveals a narrow ridge of scales like a Mohican haircut - strictly, the thoracic crest (below).

Pearly Underwing Peridroma saucia (side view) - Dorset 17.6.26

While three of the commonest immigrant moths to Britain are classed as micro-moths (see my previous migrant moth blog), only one of the present group of eight falls within that category. It's one of my favourite species - the Olive-tree Pearl Palpita vitrealis (below), after which this wildlife blog was named. There were 5,065 records of this species between 2010 and 2019.

Olive-tree Pearl Palpita vitrealis -Dorset 10.8.20

Identification is straightforward, as the combination of plain, translucent white wings with a brown leading edge (costa) appears in no other British moth species. While the wings of the Box-tree Moth Cydalima perspectalis are translucent, they usually have thick black edges - and the moth is much larger.

Olive-tree Pearl is a member of the crambid family, many of which seem to have a yearning to travel long distances; these include two very common migrants (Rusty-dot Pearl Udea ferrugalis and Rush Veneer Nomophila noctuella) featured in my previous blog and a number of much rarer arrivals to our shores. Primarily an old world species, Olive-tree Pearl is found in Europe, Africa and Asia: I have recorded it in India (Goa), where it was a nice surprise to see a familiar moth in such exotic surroundings.

Despite its name, the caterpillars of Olive-tree Pearl feed on a variety of species including Ash, privets, forsythias, Strawberry Tree and Summer Jasmine as well as Olive. To date, there are no records of it having successfully bred in Britain, although egg-laying has been observed. Once again, the moth cannot successfully over-winter here.

Heading back into the world of macro-moths, our sixth species is Bordered Straw (below), with 3,789 records between 2010 and 2019.

Bordered Straw Heliothis peltigera - Dorset 21.9.20

Bordered Straw is a helpfully distinctive moth. Despite some variation in its background colour (see below), the overall pattern of markings is generally consistent: a dark kidney mark contrasting with a lighter and plain background. Compare these images with those of Scarce Bordered Straw earlier in this post: Bordered Straw looks 'cleaner', especially in its lighter forms.

Predominantly an old world species, the range of Bordered Straw is centred on Southern Europe, North Africa and West Asia. Unlike the other moths described in this blog post, it is sometimes seen flying during the day searching for flowers. I spotted a day-flier on Grange Heath, Dorset last month (below), showing the dark band on its hindwing which is usually hidden when the moth is at rest.

Bordered Straw Heliothis peltigera - day flying at Grange Heath, Dorset 22.5.26

Like the Vestal, as already described, the background colour of Bordered Straw is affected by the temperature experienced at the larval (caterpillar) stage, with lighter individuals likely to have bred in warmer climates. Early arrivals to our shores can breed here, giving rise to a second generation that can appear darker than the first arrivals: compare the September individual above with one from in June (below) which was almost certainly a migrant arrival. However, the moth is unable to over-winter here.

Bordered Straw Heliothis peltigera - Dorset 25.6.25

Coming in at number seven, the Convolvulus Hawk-moth (below) is one of the largest moths found in Britain. It is of a similar size to the resident Privet Hawk-moth and only beaten by the massive Death's-head Hawk-moth, an extremely rare migrant species that has yet to find my garden (but I live in hope). There were 3,475 records of Convolvulus Hawk-moth between 2010 and 2019.  

Convolvulus Hawk-moth Agrius convolvuli - Dorset 6.9.16

While the plain and streaky wings of Convolvulus Hawk-moth are similar to those of Pine Hawk-moth, the size difference easily separates the two species - the wing length of Pine Hawk-moth rarely exceeds 40 mm while Convolvulus can reach 55 mm. That is in the size range of Privet Hawk-moth, which also has pink stripes on its abdomen. However, Privet Hawk-moth has a distinctly black thorax (not grey) as well as dark-brown forewings and (if visible) two black bands on the hindwings, all features that are missing from Convolvulus Hawk-moth.

In Britain, Convolvulus Hawk-moths tend to arrive late in the season with numbers peaking in September. Adults are particularly attracted by the nectar of tobacco plants (Nicotiana) and can be observed feeding on flowers at dusk. Some moth enthusiasts have this plant in their gardens for that purpose; I'm afraid that I don't, but I still manage to see a few Convolvulus Hawk-moths here in Dorset each year. 

Like the previous two species, Convolvulus Hawk-moth is restricted to the old world, and is distributed widely across Africa, Asia, Australia and Southern Europe - although most European records appear to relate to individuals that have travelled from Africa. Those arriving in Britain may well mainly be the offspring of these first generation migrants, hence the late arrival times. While the moth's larval foodplants (bindweeds, as the name would suggest) are frequent in Britain (especially in my garden), the climate appears too severe to allow it to over-winter here. 

 

Convolvulus Hawk-moth Agrius convolvuli giving a me sharp stare - Dorset 26.9.24

Which brings us to the last species in this brief survey - the Gem (below). Although this geometrid just meets my 3,000+ criterion (the 2010-2019 figure being 3,038 records), it has (for me) been the the most elusive of this group of migrants. It wasn't until 2024 that I finally saw one and, to date, I've only had two more records here (both in 2025). I have no idea why this species doesn't seem to favour my trap, and I'm trying not to take it personally.  

 

Gem Nycterosea obstipata (male) - Dorset 2.5.25

The Gem is not a very conspicuous moth, being slightly smaller than Garden Carpet. Unusually for a moth, the male and females have different wing markings (sexual dimorphism, in the jargon). The females have dark wings, with a distinct black dot edged with white - presumably the 'gem' of the common name. (All of my Gem captures have been males, so I don't have a picture of the female. However, there's a good image on the UK Moths website here.) Males have a lighter brown or orange-brown wings, with many cross-lines. While there is also a black dot, this usually lacks the white ring, although a lighter circle is visible in my image above. 

Primarily a European species, the Gem is another migrant that can breed, but not overwinter, in Britain. In Dorset, it can occur at any time between April and December; my three records were in April, August and November. While most moth migrants to our shores are more common in the south and east, the Gem seem to particularly favour these areas and has tended not to venture north of Yorkshire and Furness - or over into Ireland for that matter. Having said that, its British distribution increased significantly between 1990 and 2016 (Randle et al, 2019), so this migrant may become a more familiar sight in northern latitudes. And, I hope, in my Dorset moth trap. 

Right - this 'gang of eight' concludes my brief survey of Britain's most common migrant moths. As will be seen from the Atropos website mentioned above - or indeed any good field guide - very many more moth species reach our shores, but most arrive in much smaller numbers (sometimes only single figures). While I have been lucky to see a number of real rarities (perhaps the subject of a future blog), many more migrants have eluded my trap, which is both a matter of frustration (especially when other Dorset moth recorders have been more successful - you know who you are!) but also a useful incentive to go on searching. But be warned - hunting for migrant moths can become a bit of an obsession ...

References

Emmet, A. Maitland (1991) The Scientific Names of the British Lepidoptera: their history and meaning. Harley Publications.

Parsons, M. and Clancy, S. (2023) A Guide to the Pyralid and Crambid Moths of Britain and Ireland. Atropos Publishing.

Randle, Z. et al. (2019) Atlas of Britain and Ireland's Larger Moths. Pisces Publications.

See also the field guides and websites listed in a separate blog post (notably Waring & Townsend and the Dorset Moths website).

Atropos migrant moth totals are here.

Global range data is from GBIF.

Text and images (c) Mike Hetherington

Silver-studded Blues on the Purbeck Heaths

Male Silver-studded Blue - Scotland Heath, Dorset

Britain's resident butterflies can be divided into two main groups - the wider countryside species and the habitat specialists. You will see the first group in gardens, parks and farmland - Large White, Meadow Brown and the like. Many are very mobile, and they can turn up pretty much anywhere. Most are familiar to us. 

You have to work harder to find the second group - our habitat specialists. These are restricted to certain special places, for example where their foodplants grow, and they are less likely to travel over the wider landscape. You usually have to make an effort to find them!

The Silver-studded Blue Plebejus argus is a classic habitat specialist. In the UK it is mainly found on lowland heaths and certain parts of the English and Welsh coasts (see the distribution map on Butterfly Conservation's helpful fact sheet). But this doesn't tell the whole story. The odd fact about Silver-studded Blues is that they live in two contrasting habitats, where the plant species are very different.

We see this in Dorset, south-west England. Here, most Silver-studded Blues are found on lowland heaths in the Poole Harbour basin area, particularly in the Purbeck area south of Wareham. These heathlands are famously the home of a range of rare and often endangered species - ranging from the charismatic Sand Lizard (see my blogs here and here) to the more obscure Purbeck Mason Wasp (see my blog here).

Silver-studded Blue habitat - Scotland Heath, Purbeck, Dorset

However, you can also come across Silver-studded Blues on Dorset's Isle of Portland, where the lime-rich grassland looks very different to Purbeck's heather and gorse-dominated heathlands. There is a clear gap between the two populations, and there is little (actually, no) evidence of the butterflies moving between the two areas. So, what's going on here? To answer the question we need to look at the butterfly and its unusual ecology.

Introducing the Silver-studded Blue

Although the blue butterflies (part of the Lycaenidae family) are some of Britain's more eye-catching insects, telling the various species apart is not always straightforward - even in Britain with its relatively low butterfly diversity. Silver-studded Blue males are perhaps most easily confused with Common Blues, which are much more, well, common. As well as being smaller, the most obvious difference is that male Silver-studded Blues have a wider black margin on the wings than male Common Blues (see the photos below).

Male Silver-studded Blue - Grange Heath

For comparison: male Common Blue - Powerstock Common

At which point, you might be asking: what about the 'silver studs'? These are actually on the back of the wings, and they are not always very obvious. Look for the small bright dots in the middle of the black spots - one is arrowed in the image below: 

Male Silver-studded Blue - wing underside. 'Silver studs' arrowed.

The 'silver studs' are also present on the underside of the female's wings, which is just as well because the females - which have dark brown wings - are otherwise tricky to separate from the females of Common Blue, Brown Argus and a few others. The studs can (just about) be seen in this image of a female below (there is a better image later):

Female Silver-studded Blue - Scotland Heath

Luckily, Silver-studded Blues are not difficult to find, as long as you are in the right place. Over the last few weeks I have been carrying out wildlife surveys on the Purbeck Heaths (not for butterflies, as it happens) and Silver-studded Blues have been one of the most numerous and conspicuous insects that we have encountered. They have a characteristic flight pattern, keeping low over clumps of heather, pausing often to rest on flowers. They usually won't fly far from where you first see them; some research says that they rarely move more than 10-20 metres, although from what I've observed this may be an underestimate.  

Unusual Life Cycle

Silver-studded Blue caterpillars (larvae) have two types of foodplants, depending on their habitat. At the Dorset heaths, they feed most commonly on heathers (Calluna vulgaris and species of Erica), while on Portland's limestone grasslands it is more likely to be Bird's-foot Trefoil, Common Rock-rose or Horseshoe Vetch. So far, so different.

What links the two habitats is the relationship between the caterpillars and ants - specifically black ants. The caterpillars produce sugar-rich liquids that attract and feed the ants; in return, the ants look after the caterpillars. It seems that the ants move the caterpillars into underground chambers, from where they emerge at dusk to feed (possibly carried by the ants). Eventually, the butterfly caterpillar will pupate underground, and an adult will emerge in turn. This all seems very benign, and I can't find any evidence of more sinister behaviour taking place, such as caterpillars feeding on the ant brood, as happens with the (even rarer) Large Blue

The ant-caterpillar relationship doesn't happen by chance. Adult female Silver-studded Blues can detect chemical signals (pheromones) produced by the ants, which they will follow to find suitable a site for egg laying. On Purbeck's Grange Heath a couple of weeks ago we were lucky to find a Silver-studded Blue surrounded by black ants:

Silver-studded Blue male with black ants

Nearby, a pair of Silver-studded Blues were mating: the 'silver' studs on the female (more easily seen here) are almost blue in colour. 

Silver-studded Blues mating - male above, female below

While the association with black ants takes place in both habitats, the species of ant differs. On acid heathland it's usually Lasius niger, while on limestone grassland it will be Lasius alienus. I don't know enough about ants to distinguish them in the field, but I presume that the ones photographed above on Grange Heath were L. niger. (If they aren't, please let me know!)

Conserving Silver-studded Blues

In Britain, the combination of recent population decline and restricted distribution of Silver-studded Blues mean that they are classed as 'vulnerable' on the UK Red List, although the species is much more widely distributed in continental Europe. The good news is that even in England and Wales they are usually present in good numbers on the sites where they occur. Even better, numbers have risen dramatically on sites in Purbeck such as Studland, although the picture is less encouraging for the grassland population on Portland (Warren et al., 2025).

On heathland, conservation management aims to maintain a patchwork, or mosaic, of different ages and types of heather as well as some bare ground. Suitable grazing and/or burning can achieve this. For grassland, it is important to manage grazing levels so they do not become too excessive; creation of bare ground areas is also recommended. Such actions will benefit other heathland species too.  

Finding Silver-studded Blues

The photos of Silver-studded Blues in this blog post were all taken on the Purbeck Heaths, which is where (in my experience) the butterflies are most easily found in Dorset. While I have seen them on Portland, numbers there are lower than at Purbeck, and there is also a greater risk of confusing them with other blue butterflies. Chalk-hill Blue and the beautiful Adonis Blue are present on Portland's limestone grassland, but absent from Purbeck's acid heaths. The flight period runs from mid-June to the end of August, so now's the time to get out and look for them.  

Many of Purbeck's heathlands are accessible to the public, and most lie within the Purbeck Heaths National Nature Reserve (link here). At RSPB Arne (where I volunteer), Silver-studded Blues can be seen from the trails on Coombe and Hyde's Heaths.

 

Male Silver-studded Blue - Grange Heath

References

Asher, Jim, Warren, Martin, Fox, Richard, Harding, Paul, Jeffcoate, Gail and Jeffcoate, Stephen (2001). The Millennium Atlas of Butterflies in Britain and Ireland. Oxford: OUP.

Hetherington, Mike, Sterling, Phil and Coulthard, Emma (2022). 'Butterfly colonisation of a new chalkland road cutting.' Insect Conservation and Diversity, 15(2), pp.191-199. - link

Munns, Lorraine (2017). Is it all about the ants? What are the factors influencing the presence of Plebejus argus (the Silver-studded Blue butterfly) on Studland Peninsula? (Doctoral dissertation, Bournemouth University).

Sterling, Phil and Henwood, Barry (2020). Field guide to the caterpillars of Great Britain and Ireland. London: Bloomsbury.

Thomas, C.D. (1993). 'The silver-studded blue, Plebejus argus L.' The conservation biology of Lycaenidae (butterflies), pp.97-99. - link

Thomas, Jeremy, Surry, Richard, Shreeves, Bill and Steel, Carolyn (1998) New Atlas of Dorset Butterflies. DNHAS.

Tolman, Tom and Lewington, Richard (2008) Collins Butterfly Guide. London: HarperCollins. 

Warren, M.S., Rich, S. and Haywood, N. (2025). 'The dramatic rise of the Silver-studded Blue, Plebejus argus, over 50 years at Studland Heath National Nature Reserve, Dorset, UK' - link

Text and images (c) Mike Hetherington

Purbeck Mason Wasps - a star of Dorset's heathlands

 

Purbeck Mason Wasp Pseudepipona herrichii - Grange Heath, Dorset

One of the joys of surveying for reptiles on the Dorset heathlands is the likelihood of being distracted by other exciting wildlife. And this morning on Grange Heath, in the growing heat of June, there was much of interest to distract us - mostly of the insect variety. 

Star billing went to the Purbeck Mason Wasps Pseudepipona herrichii (see image above). Within the British Isles, this handsome hymenopteran has an incredibly restricted range. Essentially, it is only found on the lowland heaths around Poole harbour in the east of Dorset, especially in what is generally known as the 'Isle of Purbeck'. (Spoiler alert - it's not even slightly an island). I've added a link to NBN Atlas distribution map for the species here - the pattern is pretty stark.

Purbeck Mason Wasps are one of the UK's rarest invertebrates, which has been recognised by law: they are a 'priority species' for conservation in the Natural Environment and Rural Communities (NERC) Act 2006 (section 41). A 'species action plan' was published in 1999 (link here) describing actions and activities aimed at improving the wasp's conservation status. This has been taken forward by the 'Back from the Brink' project, with a useful summary sheets here and here.

Grange Heath lies in a quiet, and rather isolated, corner of the wider Purbeck Heaths National Nature Reserve (more details about the overall reserve are here). The land is managed by the RSPB, who make no secret of the presence of Purbeck Mason Wasps on the site:

Grange Heath entrance sign

The heath is managed for several species of conservation interest, including birds, reptiles and invertebrates. Populations are monitored, and it was reptile monitoring that took us to the site this morning. Various actions have been carried out on the heath to benefit Purbeck Mason Wasps, but to fully understand these we need to take a quick look at the ecology of this - frankly rather fussy - species. 

Like many insects, these solitary wasps have a bizarrely specialised life cycle, which probably accounts for their rarity. After winter, males are the first to emerge; they have a short life span, existing only to mate with the females before dying after about 10 days. Not much of a life, you might say. After that, the females do all of the work - and their first job is to dig a burrow, as seen in a short iPhone video from this morning:

Although classed as 'solitary wasps', individual females seem to prefer nesting in groups - although this may be due to the relative scarcity of suitable sites for burrowing. The wasps need open ground that has a high clay content: if it is too sandy then this risks the burrows caving in. The holes are neat and round, with the burrows heading vertically down. The spoil from digging is usually moved slightly away from the hole, so it's worth looking for a small pile of soil granules in the vicinity. The photo below, from this morning at Grange Heath, shows Purbeck Mason Wasps at the entrances of two burrows plus a third burrow (arrowed): 

Purbeck Mason Wasp burrows - two occupied and one empty (arrowed)

At Grange Heath, a number of artificial scrapes have been excavated in suitable clayey substrates - and this has obviously worked. Almost all of the Purbeck Mason Wasps that we saw were buzzing around these cleared areas - and we saw well over 20 individuals.

However, finding suitable ground conditions is only part of the challenge for a female Purbeck Mason Wasp. What makes the wasps unique (you might say 'picky') is their feeding strategy. This has two parts. The adult females seek out a high energy food source in the form of nectar. However, only one species of plant will do: Bell Heather Erica cinerea. The wasps' tongues aren't long enough to reach into the tubular openings of these richly purple-coloured flowers, so they have to bite through the base of the flower (the calyx) to obtain nectar. The presence of Bell Heather is therefore another habitat requirement for the species. Fortunately, there's plenty of this on Grange Heath.

The second part of the feeding equation involves provisioning the wasps' offspring, and (once again) only one type of food will do. This time it's the caterpillars (larvae) of a small heathland moth variously known at Heath Tortrix, Heath Button Moth or (more scientifically) Acleris hyemana. The unfortunate larvae are caught by the female wasps, brought back to base and stuffed into the newly dug burrow. An egg is then laid on top of a ready-made food source for the growing wasp larva. Grisly, but not unusual in the insect world.

But it doesn't always go to plan for the wasp. The female will usually leave the burrow unsealed in her search for several moth larvae to feed her future brood. This provides an opportunity for Black Ants Formica fusca to nip in and steal the hapless moth larvae, which will then be taken back to the ants' nest for a similarly unpleasant end. We were fortunate this morning to see a caterpillar in the process of being moved by some ants from one of the many nearby wasp burrows (below). 

Acleris hyemana larva being moved by Black Ants

Any strategy aimed at conserving the wasps must therefore also seek to conserve the moths. While these have a wider distribution than that of the wasps (NBN distribution map link here), they are not always common in heathland environments, showing a clear preference for shorter and younger heather. Managed burns of small areas of heathland can achieve this, as happens at Grange Heath. 

The story of the Purbeck Mason Wasps provides an insight into both the complexity of heathland ecosystems and the challenges of conserving what are often rare species in the British context. But it's surely worth it in order to maintain the interest and diversity of Dorset's fabulous lowland heaths.

Purbeck Mason Wasp entering burrow - Grange Heath, Dorset

Acknowledgements

 

Particular thanks to my sharp-eyed fellow reptile surveyors (Howard, Chris, Sue and Rob) for their help in locating wasps, burrows, larvae and ants at Grange Heath this morning, and to all the RSPB Dorset Reserves team involved in protecting and managing this fabulous heathland site.

Thanks also to Phil Sterling for confirming identification of the Acleris hyemana larva.

Introducing Common Migrant Moths (part 1) - the Big Seven

It has been a slow start to the year for moth recording, but everything changed last night (22 May 2026) with the arrival of warm air from the south (likely from North Africa). Such conditions are ideal for finding migrant moths down here on the Dorset coast, and I approached the trap this morning with some anticipation. As well as bleary eyes: I was up at 4.20am, arriving only just before our local Robins and House Sparrows.

The final trap tally was almost 200 moths from 69 species. Seven of these species were migrants. Moth migration is a particular interest, and this morning's arrival gives me the perfect opportunity to look at the subject in a bit more detail. In this (and the next) post I'm reviewing the common migrant species that we get in the UK, several of which turned up here this morning. 

There's much to say about moth migration, but I'll keep it short for the present post. In summary, we are talking about those moth species that arrive, but do not generally overwinter, in the UK. While early arrivals may breed successfully, their offspring are unlikely to survive the winter months. As such, they are unable to establish permanent breeding populations. For the time-being. 

This caveat is important. Over the last 20-30 years, the British Isles have seen the arrival and establishment of several moth species (such as Jersey Tiger) who's status has changed from migrant to resident breeder. Indeed, British populations of many longer established species (like Large Yellow Underwing and Angle Shades) are regularly augmented by arrivals from continental Europe or further afield. In such cases it is impossible to tell for certain whether the moth in your trap has experienced a cross-Channel journey or just flown in from a local population, although weather conditions along with the presence of known immigrant species alongside them can provide useful hints.

So - which species are the known migrants? For a newcomer this is a bit baffling, but there is help at hand. The status of British moths is explained in the better field guides (see my blog post reviewing identification resources), and migrant species are considered in some depth by the Atropos journal and website. Atropos runs a 'flight arrivals' page where recorders can post details of new sightings, although I don't post on this as often as I probably should. For users of Facebook, Steve Nash runs the Migrant Lepidoptera (GB & Ireland) group, which carries news and images of migrant arrivals. There is a similar account on BlueSky.

OK - let's have a look at the common migrant species. These are spread across several moth families, suggesting that the tendency to migrate is either an innate Lepidopteran characteristic or has evolved separately many times. Now is not the time to speculate! Certainly, some families seem to be disproportionately represented in the migrant lists - notably the Crambid micro-moths as we will see. This and the next blog do not take a taxonomic approach. Instead, they focus on abundance, describing the migrant species that you are most likely to encounter. 

This blog post starts with what I'm calling the 'big seven' - the species that are so common that absolute numbers simply cannot be obtained. Some arrive in massive influxes: for example around 3 million Silver Y moths were recorded per hour on Shetland in 1996 (quoted in Randle et al., 2019). But please note that these are only 'big' in the sense of numbers. As we'll see, one species is very small indeed.

So let's begin with the Silver Y moth (pictured below and at the start of this post). This is found across continental Europe. Flying during the day as well as night, it is a fairly conspicuous species. Look for it nectaring on flowers during a sunny afternoon - as well as in the moth trap.

Silver Y Autographa gamma - Dorset 17.5.25

It's clear how Silver Y got its name. The combined shape and colour of the obvious Y-shaped mark are usually diagnostic, but bear in mind that there are a number of moths with a similar form and resting position that could cause confusion. Several are very rare migrant species (not covered in this post), but there are two common residents that need to be ruled out - Plain Golden Y and Beautiful Golden Y (below). In both cases the Y mark is usually split and lacks the silver sheen.

Non-migrant confusion species 1 - Plain Golden Y Autographa jota - Dorset 23.6.20

Non-migrant confusion Species 2 - Beautiful Golden Y Autographa pulchrina - Dorset 15.6.18 

Silver Y is a true migrant, in that the offspring of moths that have bred in Britain have been recorded undertaking a return migration to the continent in search of warmer winters (Chapman et al., 2002). While numbers in Britain have declined, its range has increased (a curious pattern found in some other moth species). Like several other moth migrants, Silver Y is arriving here earlier in the year as climate patterns change.

The second common migrant moth is even more conspicuous - the Hummingbird Hawk-moth (below). This is largely day-flying, although a few do turn up in moth traps. It is a real crowd-pleaser, buzzing around flowering plants and bushes in a distinctly hummingbird-like manner. Getting a photo can be a real challenge: they never seem to keep still.

Hummingbird Hawk-moth Macroglossum stellatarum in action - Dorset 12.6.15

Identification is straightforward: Hummingbird Hawk-moths are unlike any of our common hawk-moths and the combination of white, black, grey and orange colours - plus the distinctive flight pattern - is diagnostic. The distribution of this species within Britain has increased markedly over the last 45 years and there is recent evidence of adults being able to successfully overwinter here. This year, one was seen as early as February here in Dorset. Globally, the range of the species stretches from continental Europe right across to East Asia.

The next two common migrant species are both members of the same family as the Silver Y (the Noctuids), but lack its particular profile and markings: they stand out less from the many other species in that large family. Nevertheless, both have distinctive characters that enable easy identification.

Unlike many migrant moths, Dark Sword-grass (below) has shown a major decrease in numbers since the 1970s. Nevertheless, it is still recorded across much of Britain, although it remains unclear whether the species has successfully overwintered here. Last year it was the first migrant moth to turn up in my Dorset trap - on 21 February 2025, which seems unusually early for a cross-Channel arrival. But you never know. Globally. the species is widespread, occurring in South America, southern Africa and Australia as well as Europe, Asia and North America where it is most commonly found.

Dark Sword-grass Agrotis ipsilon - Dorset 16.3.23

Superficially, Dark Sword-grass looks like many other large noctuid species, but it has a particular diagnostic feature enabling easy recognition - a narrow black triangle ('dart') protrudes from the kidney mark (facing down in the above photo), with two more black darts pointing towards it from the end of the wing. See the enlarged image below:

Dark Sword-grass - detail of wing marking

The last noctuid in this list - the Delicate (below)- has a distinctly southern and eastern distribution in Britain. It is rare in Scotland and North Wales.

Delicate Mythimna vitellina - Dorset 7.6.17

The light (delicate?) tracery of wavy brown cross-lines on a lighter background is pretty much unique to this species, although the background colour can vary. Paler adults, such as the one pictured above, have been shown to result from more rapid development at higher temperatures - so have probably arrived from somewhere hot and dry like southern Spain. Globally, the species is restricted mainly to Europe although it has also been recorded in the Canary Islands.

The remainder of the 'big seven' are all 'micro-moths' - see another post for more about the differences between 'micro' and 'macro' moths. The first two lie within the Crambid family, which contains some of my favourite moth species.

At first sight, the Rusty-dot Pearl (below - from this morning) appears relatively undistinguished. However, once you have got your eye in, its characteristic warm orange-brown colour with (usually) darker oval and kidney markings coupled with a strongly triangular shape clearly point to this species. Globally, the species has a large range that extends from Europe to South Africa and Japan.

Rusty-dot Pearl Udea ferrugalis - Dorset 22.5.26

The second common Crambid migrant, Rush Veneer (below, also from this morning), is more variable in colour and pattern than Rusty-dot Pearl. Fortunately, its long and narrow shape cannot be confused with any other common British moth (although there is a similar American species). The one pictured below is quite light in colour: others can be darker. The species has a similarly wide global range to Rusty-dot Pearl.

Rush Veneer Nomophila noctuella - Dorset 22.5.26

The final 'big seven' migrant is anything but big! The Diamond-back Moth (below) is absolutely tiny, about 6-8mm in length. You can easily miss them in a moth trap. Yet this minute insect is one of the world's great travellers, turning up in every continent except Antarctica (although I bet that a few have turned up there as well that no-one has yet discovered). They fly both during the day and night.

Diamond-back Moth Plutella xylostella - Dorset 24.5.18

Identification is fairly straightforward (if you can spot them in the first place); in their characteristic form, the wavy-edged light patch on the back provides a clear contrast with the dark sides of the moth. Given their small size, some form of magnification is helpful to make this out.

Diamond-back Moths can arrive in huge influxes, and in some years are probably the most abundant of all of the 'big seven' migrants to Britain described above. For example, hundreds of thousands arrived in May 2000, probably from Southern or South-eastern Europe (Chapman et al., 2002). There were only five in my trap this morning, but to witness a mass arrival is an impressive sight that I have only experienced once - on the island of Inner Farne off the coast of Northumberland several years ago, where every bit of vegetation seemed to be dotted with tiny moths.

It's worth adding that Diamond-back Moths can be a serious agricultural pest. The Natural History Museum has published a short article about the species here.

Right - those are Britain's top seven most common migrant species. The next blog will look at those that are a bit rarer, but still turn up in sizeable numbers. Watch this space.

References

Chapman, J.W., Reynolds, D.R., Smith, A.D., Riley, J.R., Pedgley, D.E. and Woiwod, I.P. (2002). 'High‐altitude migration of the diamondback moth Plutella xylostella to the UK: a study using radar, aerial netting, and ground trapping.' Ecological Entomology, 27(6), pp.641-650. (link)

Chapman, J.W., Lim, K.S. and Reynolds, D.R. (2013). 'The significance of midsummer movements of Autographa gamma: Implications for a mechanistic understanding of orientation behavior in a migrant moth.' Current Zoology, 59(3), pp.360-370. (link)

Parsons, M. and Clancy, S. (2023) A Guide to the Pyralid and Crambid Moths of Britain and Ireland. Atropos Publishing.

Randle, Z. et al. (2019) Atlas of Britain and Ireland's Larger Moths. Pisces Publications.

See also the field guides and websites listed in a separate blog post.

Global range data is from GBIF.

Dartmoor Highlights - and a question of ethics

The Common Redstart (above) may be Britain's most attractive summer visitor, but it's getting increasingly difficult to track one down. In Dorset, where I'm based, they are very scarce breeders, more usually seen passing through the county on migration. Which makes the perfect excuse for a birding excursion over the border into Devon. 

A spring visit to Dartmoor is an annual event in my birding calendar - see this post from a couple of years ago. Two locations take centre stage. My first stop this morning was Yarner Wood, which has the honour of being England's first National Nature Reserve (NNR), established in 1952. Now expanded into the East Dartmoor NNR, the site is managed by Natural England. A leaflet about the reserve can be downloaded here (1.9MB).

The oak woods at Yarner are positively festooned with bird and bat boxes. The first nestboxes that I came across were all occupied by Blue Tits, and the busy comings and goings of the parents showed that nestlings were in residence. But further up the track a dart of black and white revealed the presence of a male Pied Flycatcher (below). He perched conveniently close to the path:

Pied Flycatcher (male) - Yarner Wood, Devon, UK

Nationally, Pied Flycatcher number have decreased massively - a 53% drop between 1995 and 2023 (see the data from the British Trust for Ornithology here), although losses appear to have levelled off - possibly as a result of nestbox provision in places like Yarner Wood. My non-scientific impression this morning was that numbers seem similar to my previous visits.

Unfortunately, the same can't be said for Wood Warblers, which the official NNR leaflet says that Yarner is 'famous' for. Not now, I'm afraid. It's many years since I last saw or heard a Wood Warbler there - and none were apparent this morning.

My second destination of the morning was Emsworthy Mire, a Devon Wildlife Trust reserve at the head a valley just below Haytor. The sun was out, but a sharp wind was blowing.

  

View over Emsworthy Mire, Dartmoor. Haytor in the distance.

I could hear a singing Common Redstart as I entered the reserve, following the path that winds between a network of dry stone walls that mark out the site of this former farm. Some of the fields contained a stunning display of Bluebells - the best that I've seen there.

Bluebells at Emsworthy Mire

On previous visits I have watched Redstarts in the vicinity of the old barn that sits roughly in the centre of the reserve. It is surrounded by mature trees (mostly Sycamore) which contrast markedly with the more windblown Hawthorn and Ash dotted around the fields. As I approached the barn, I saw that a couple of other guys with cameras had beaten me to it. A female Common Redstart hopped onto a stone wall, but speedily disappeared. A male then flew up into a nearby tree ...

... and then descended to perch on an old stone wall right in front of me:

Common Redstart (male) - Emsworthy Mire, Devon

This was fantastic, although I couldn't help but wonder why he had come so close to the path. The answer was soon apparent:

Common Redstart with mealworms (not placed there by me)

Mealworms do not naturally inhabit the top of stone walls, and one of the photographers must have placed them there. My initial feeling was one of disappointment, as I was not observing the bird's natural behaviour. But then again, I was pleased to get such good views and I'm very happy with the resulting images. It's a bit of an ethical dilemma.

To be clear, I would never bait a site in order to obtain a photograph - but then photography has never been my prime motivation when watching birds (or indeed any other wildlife). Having said that, it's always very satisfying to have a nice picture that records the things that I have seen, and in some cases such a photo can also act as a useful identification tool. Before writing this blog post, I had a bit of an online dive into various birding websites and forums and I see that my dilemma is shared by many. A good example is this article by Pete Garrity, which rehearses these arguments (and more) in some detail; I certainly agree with his key take-home message that the welfare of the bird must come first. There is a similar conclusion in a thoughtful blog by Adam Juckes, who emphasises (correctly in my view) that much depends on the particular circumstances of each case.

As it happens, supplementary feeding is in the news at the moment, with the well-publicised change of stance by the RSPB - link here (in summary: feed seasonally, feed safely).  The spread of diseases like trichomonosis is part of the problem, but recent research also has highlighted the potential for ecological harm to arise from the provision of additional food in certain circumstances - for example by giving a competitive advantage to bird-feeder visitors (like Great Tits) over declining insect-feeders (like Pied Flycatchers) (Broughton et al., 2021). I've stopped putting out bird feeders in my garden for this reason. But we have to acknowledge that in the wider world, supplementary feeding is well established - many (if not most) eco-lodges in the Neotropics will have fruit and nectar feeding stations for toucans, tanagers, hummingbirds and the like - and I have spent many happy hours watching (and indeed photographing) the birds that visit them. 

There are no easy answers, and in many cases it will simply be a case of fact and degree. The occasional baiting of a site like Emsworthy is unlikely to cause material harm and may indeed provide some benefit to the bird(s) concerned. The Common Redstart seemed happy enough to accept an easy meal. In an ideal world, photographers using this method should perhaps 'come clean' as to how they obtained their image, but that might be asking too much!

But as soon as a rare and infrequent practice becomes widespread then alarm bells should start to ring. At that point, much more serious thought needs to be given about the likely effect on the species concerned. This becomes particularly important when birds are the subject of conservation concern, a factor that is recognised in the UK by various laws (unnecessarily complicated in my view, but that's a separate discussion) that protect certain species - notably Schedule 1 of the Wildlife & Countryside Act 1981 (as amended) (explained here) in respect of breeding birds. As it happens, Common Redstart is not (at time of writing) a Schedule 1 bird, but its range has declined in recent years along with a slight population decrease (information from the BTO on this is here). To me, this suggests that we should think very hard when carrying out actions like supplementary feeding that could affect its natural breeding behaviour. But perhaps I'm being over-cautious. And clearly there are many more pressing problems affecting wild birds such as habitat loss, climate change, pesticide use, agricultural intensification, hunting ... the list goes on.

My visit to Emsworthy finished on a less controversial note. I didn't linger by the barn, heading off instead on the circular route that runs around Emsworthy Mire. I was near to the south-western corner of the reserve when I finally heard the call of a male Cuckoo nearby. He was easy to locate:

Cuckoo male - Emsworthy Mire

  And he wasn't alone. A female was nearby, resting on a fencepost:

Cuckoo female - Emsworthy Mire

Neither of these are great photos, but I was keeping my distance in a landscape that offered very little natural cover. Not that the Cuckoos appeared unduly bothered; they were more occupied with each other - the male calling loudly and flying after the female when she moved further along the fence line. At the same time, both Cuckoos were being repeatedly mobbed by other birds - mostly Meadow Pipits. You can understand why, of course, although what baffles me is that the same birds fail to recognise a giant Cuckoo chick in their own nest. There is much of interest in the life of the Cuckoo. 

My last view of was of both Cuckoos sitting almost side by side further along the fence (below). Note the Meadow Pipit on the middle post. Both birds then flew away across the moor.

Reference

Broughton, R. Shutt, J. and Lees, A. (2021) 'Rethinking bird feeding: are we putting extra pressure on some struggling woodland birds?' British Birds, 115 (1). pp. 2-6.