Seeking the Heath Tiger Beetle

As readers of this blog will know, I have been spending some time this year doing surveys on Dorset's Purbeck Heaths National Nature Reserve for the RSPB, ARC and the Purbeck Natural History Forum. Mostly these were reptile surveys, but I've also strayed into other taxa, such as the fascinating Purbeck Mason Wasps and Heath Tiger Beetles which are the subject of this post.

Heath Tiger Beetle Cicindela sylvatica - Wareham Forest, Dorset 2026

So - what are Heath Tiger Beetles and why are they of interest?

As a group, tiger beetles are agile and voracious hunters. Fast moving, with large eyes and larger jaws they move at speed in search of a range of small invertebrate prey. There are five species in Britain, only one of which is widespread and well-known - the Green Tiger Beetle (below). I've seen these in a range of habitats including lowland heath (such Arne in Dorset), bogs (the Shropshire meres) and upland grassland (Brecon Beacons) - but never in an intensively farmed area. Look for them in Britain's wild places (see NBN Atlas distribution map).

Green Tiger Beetle Cicindela campestris - Bovey Heath, Devon 2013

The Heath Tiger Beetle is one of the other four rarities. In Britain, it is exclusively a species of lowland heaths, with almost all records coming in a belt running from the east Dorset heathlands up to Surrey - see the NBN Atlas map. But do not be fooled by the satisfyingly large splodges on the large scale version of this map. If you drill down into the detail, you will see that even within apparently favoured habitats, the actual distribution of the species is patchy at best. 

What Heath Tiger Beetles seem to like are low-lying moorlands with a mosaic of different aged heather (Calluna and Erica) interspersed with open sandy areas. The photo below shows Heath Tiger Beetle habitat in Wareham Forest, Dorset. Bare ground is important for a number of reasons. Adults use it for hunting, and also to warm up out of the shade on cooler mornings. Sandy areas are also used by Heath Tiger Beetle larvae, which dig burrows before moulting (they probably undergo three moults) and eventually pupating. They can spend 1-3 years underground, emerging to hunt, while adults can live a further one or two years. Summer is the time of greatest adult activity, especially between May and July. 

Heath Tiger Beetle habitat - Wareham Forest, Dorset

Heath Tiger Beetle numbers have been in decline, in line with the loss and fragmentation of Britain's lowland heathlands. It is on the Red List of endangered species. The good news is that conservation action is already underway. General protection of heathland habitat from fire and encroachment by gorse, pine or (even worse) development is the obvious starting point, but more targeted action has been carried out with the creation of around 300 scrapes - strips of bare land several metres wide - at eight sites across Dorset's Purbeck Heaths and Wareham Forest. This has shown encouraging results, with an increase in recorded sightings. Ongoing monitoring is an important part of this process, which is where the Purbeck Natural History Forum surveys come in.

I was keen to get involved this summer, but came rather late to the party as I had no prior experience of the species. If you're doing a survey then you need to know what to look for. Advice from Howard Inns pointed me to a site in Wareham Forest, where I headed in mid-June to find my first Heath Tigers. Early omens were good, as I almost immediately came across a lovely female Sand Lizard watching me through the cover of a gorse bush next to the path (below). This was a nicely undisturbed place.

Sand Lizard - Wareham Forest, Dorset

Nevertheless, the Heath Tiger Beetles initially proved elusive. I spent about 15 minutes walking suitable trails without a beetle in sight, before reaching some of the scrapes mentioned above. And, as if on cue, the beetles appeared - at least 10 individuals.

Both Heath and Green Tiger Beetles have a distinctive pattern of behaviour that makes them easy to spot once you've got your eye in. (Or course you then need to check that you have the correct species, as both are present on the Dorset heathlands.) Look for a fast-moving beetle patrolling across the bare ground. As you approach, the beetle will almost certainly fly off, keeping low to the ground, landing a metre or so ahead. The trick is to note where it lands, approach slowly and then observe it with a pair of close-focussing binoculars - plus, in my case, a long camera lens:

Heath Tiger Beetle - Wareham Forest, Dorset 2026

The beetles are more easily seen against light-coloured sandy soil. In the deep heather they would be almost impossible to spot, which raises the question of whether they occur more widely across the heathland but are only recorded from bare ground because this is where we can see them, The jury may still be out on that one.
 

The rest of the tale is one of anticlimax, I'm afraid. After my Wareham Forest initiation I went on to survey Scotland Heath (one of the Purbeck Heaths) for Heath Tiger Beetles, but found none. Given the relative lack of bare ground on that site, this wasn't a huge surprise, although I did come across some Purbeck Mason Wasps which was a bonus. Later on in the season I also walked over a known site for Heath Tiger Beetles on Purbeck (Slepe Heath), but only managed a single sighting - and that one escaped into the heather before I could get a photo. It was however on an incredibly hot July afternoon, so possibly not the best time for carrying out a survey.  

But at least I'll be ready for next year.

Afterword

A couple of additional points for the sake of completeness.

There is some confusion about the Heath Tiger Beetle's common name. Some publications refer to it as Wood Tiger Beetle, which is in line with its scientific species name - the 'sylvatica' bit of Cicindela sylvatica. The problem with this is that, in Britain at least, you find only them on heathlands and not in woods. So for this blog I've stuck with Heath Tiger Beetle.

I should also briefly mention Britain's other three tiger beetles, all of which I have yet to track down. All have even more restricted distributions than Heath Tiger Beetle, although Luff (2007) says that they can be 'occasionally abundant'. Two are from the same genus as Heath Tiger Beetle and look very similar. (Beetle experts will tell you that the distinction is that Heath Tiger Beetles have a black, not yellowish, labrum - the flat bit between the head and the jaws - but location and habitat are the easier initial pointers towards identification). Dune Tiger Beetle Cicendela maritima is (as its name suggests) found on coastal sand dunes, mostly in north Devon and south and central Wales. Cicindela hybrida (no common name) also lurks in dunes, but only in Lancashire and south Cumbria. Britain's final tiger beetle is Cylindera germanica (no common name, again), after having been booted out of the genus Cicindela by taxonomists. It has a similar colour to Green Tiger Beetle (metallic green) but is thinner with fewer spots. It's found on coastal grassy slopes in Dorset, Hampshire and the Isle of Wight, so it's one that I really need to check out. Watch this space.

References

Luff, Martin L (2008) Provisional atlas of the ground beetles (Coleoptera, Carabidae) of Britain. Biological Records Centre Institute of Terrestrial Ecology - link

Luff, Martin L (2007) The Carabidae (ground beetles) of Britain and Ireland. Royal Entomological Society Handbooks for the Identification of British Insects, vol 4(2) (2nd ed.)

Jones, Richard (2018) Beetles. (New Naturalist). London: HarperCollins

Websites

Species study - Back from the Brink

Species Recovery Trust Handbook

Vive la différence: an Anjou moth trap

Four-spotted Tyta luctuosa - Anjou, France

France is our favourite holiday destination. An easy hop over the Channel from Dorset opens up a heady mix of superb food and wine, pastoral landscapes and fascinating places to explore. There's only one snag: of necessity, most of our recent trips have taken place during the summer school holidays - a time that's generally poor for seeing wildlife. And this year (August 2026) is no exception, with temperatures down here in the Loire Valley currently peaking at a toasty 39 degrees. Animal life is generally keeping its head down, and even the butterfly numbers seem low.

But there are still moths! For a UK-based recorder, France is an exciting place to run a trap. And the further south you travel, the better it becomes. Moths that are familiar from home turn up next to species that would be major rarities on the British side of the Channel, as well as ones that have yet to make it to our shores.

For the record, I should add that I am staying in a rental cottage (gîte) in a small village around 10km north-west of Angers (Maine-et-Loire - the historic Anjou region). Being unsure of how well-separated the garden would be from its neighbours, I arrived with my low wattage (6W) battery-powered Heath-style trap. To date, I have run it on two nights, which have produced a total of 67 species and 314 individual moths - reasonable numbers for a trap of this power and type. In this post I'm just going to run through some of the highlights. 

Moth trap ready for opening.

The sight of a Portland Ribbon Wave (below) on the outside of the trap is always a hopeful sign. This species is regular in my Dorset garden, although never common; now resident in the UK, it is largely restricted to the south coast of England, but spreading north. But in France it's pretty common: there were a total of 20 in my two traps here. Portland Ribbon Wave is double-brooded in France (there's only a single brood in England), its caterpillars feeding on plants such as Yarrow.

Portland Ribbon Wave Idaea degeneraria - Anjou, France 

Another locally common species here that would cause surprise - and perhaps alarm - in the UK is Oak Processionary Moth (below). There were 15 in my two traps. In Britain, Oak Processionary is both a rare immigrant, although numbers are on the rise, and a resident that was accidentally introduced. It is a major pest of broadleaved woodland; while oak is its preferred larval food plant, it can spread onto other species during large infestations. This caterpillars are best avoided, as contact can cause skin and eye irritations; this isn't something that I've experienced personally, but if it's anything like my Brown-tail larval encounter some years ago then it will not be pleasant.

Oak Processionary Moth Thaumetopoea processionea - Anjou, France

Sitting nearby was a Pale Shoulder (below), one of five in my two traps. This exceptionally smart noctuid is a rare migrant to British shores; it has yet to make it my garden, but I live in hope. While there is some evidence that it has bred in England, there is no record of successful overwintering. Even in France the species has a generally southern distribution, being considered a migrant in the north of the country. It is also an impressive bird poo mimic.

Pale Shoulder Acontia lucida - Anjou, France

Inspecting the trap more closely, I could hardly miss a massive crambid sitting on the rain shield - a Giant Grass-moth Ancylolomia tentaculella (below). I knew straight away that it was a new species for me, which was a bit baffling as I have trapped in France before and it was not something that you would easily miss. But such is the joy of moth trapping: you never quite know what's going to turn up. Sorting out the identification was a bit of a challenge, as my standard French reference (Robineau, 2011) only covers macro-moths. It needed some searching of the web (as always, there are some great images on Lepiforum), which revealed that this is a species where males and females differ in both appearance and size - a good example of sexual dimorphism, although not as extreme as those species (such as Winter Moth) where females are wingless. Anyway, here are the female and male:

Giant Grass-moth Ancylolomia tentaculella (female) - Anjou, France

Giant Grass-moth Ancylolomia tentaculella (male) - Anjou, France

The size difference is not really apparent from these photos: for reference, the respective wing lengths are around 12-15 mm for the males and 15-20mm for the females. There are only a few British records of the species, but here it was the commonest 'micro' moth with 23 in the two traps combined.

I've already teased my star species of the night with the opening photo of this post - my first ever Four-spotted (also pictured below). Although this is resident in Britain, it is nationally scarce, with a patchy distribution that includes Dorset (notably Portland) and scattered sites through southern and eastern England. The larval foodplant is Field Bindweed Convolvulus arvensis.

A quick word about its common name: while only two (or at best three) white spots are obvious when the moth is at rest, all becomes clear when the wings are open, the white hindwing band giving the impression of two more spots (below).

Four-spotted Tyta luctuosa - Anjou, France

I encountered one nectaring the following day in the gardens of Angers Castle (which is well worth a visit); I hadn't realised that this moth also flies during the day.

  

Another day and night-flier only turned up in my second trap of the holiday: the stunning Spotted Sulphur (below), one of three. Formerly resident in East Anglia, this is now considered extinct in Britain. If it is a migrant species, it is a staggeringly rare one: the last British record seems to have been in the 1960s. Like Four-spotted, its larvae feed on Field Bindweed; the absence of both species from the British Isles may well be as a result of agricultural intensification, although other factors could have come into play. It would certainly be nice to see it again on our side of the Channel.

Spotted Sulphur Acontia trabealis - Anjou, France

The balance of species in a French moth trap can often be very different from that at home. Several groups were completely absent from the two traps that I have run down here, for example hawk-moths, tiger moths and footmen. This may be an artefact of the type of trap that I'm using, or they just may not be around this part of Anjou at the moment. Or it could be linked with the heat wave that we are experiencing here. 

In fact, the three most common species that I recorded were all noctuids. Coming in at second and third respectively were Vine's Rustic and Heart and Dart, both of which would be equally as common back in Dorset in mid-August. But at the top of the list was another French speciality - Great Dart (below).

 

Great Dart Agrotis bigramma - Anjou, France

Great Dart is a bit of a whopper as noctuids go, with a wing length of around 20mm. The size separates it from most broadly similar species, with Turnip Moth (which turned up here as well) being the main potential confusion. One of the key differences is that Great Dart has two sets of pale cross-lines with dark edges. In Britain, Great Dart is considered a scarce and infrequent migrant, but you only have to cross over to Normandy (or indeed the Channel Islands) to find it appearing as a frequent moth trap visitor.
 

The next noctuid (below) was a bit of a puzzle, and set me off looking for new species before I realised that it's actually a different form of a familiar August arrival at home - Centre-barred Sallow. The patten gives it away, with that distinctive central cross-line that could almost have been drawn by a ruler. In the British Isles this usually has a dark purple central band set against a yellowish background. However other forms are equally common on the continent including this all-brown form unicolor. 

Centre-barred Sallow Atethmia centrago (f. unicolor) - Anjou, France

While some groups of moths were missing, others seemed if anything to be over-represented - particularly the pyralid family (Pyralidae). I'm always pleased to see the lovely Rosy Knot-horn (below) - aka the Rhubarb and Custard moth; while this turns up most years in my Dorset trap, it would be unusual if it was missing from a summer moth trap in France.

Rosy Knot-horn Oncocera semirubella - Anjou, France.

Its close relative the Tufted Knot-horn (below) is a migrant to British shores, although it may now have taken root as a colonist. It's certainly more common down here in central France, with three in my second trap. The tufts of raised scales near the thorax separate it from similar species: this is quite a tricky group to identify.  

Tufted Knot-horn Acrobasis tumidana - Anjou, France

And to finish off with something completely different, I'll leave you with one of the other interesting invertebrates that also found its way into the trap - this Chestnut Weevil (below) with its impressive rostrum (projecting snout). The species occurs across western Europe, where it is a serious pest of Sweet Chestnut trees. According to GBIF there are no British records. The 'by-catch' from overseas moth traps is often as interesting as the moths themselves (heresy!), and I have a few more species to sort out from my Anjou adventure. But those will have to wait.
 

Chestnut Weevil Curcilio elaphas - Anjou, France

References

Robineau, Roland (2011) Guide des papillons nocturnes de France. Paris: Delachaux et Niestlé.

Sterling, Phil and Parsons, Mark (2023) Field Guide to the Micro-moths of Great Britain and Ireland. 2nd ed. London: Bloomsbury.

Waring, Paul and Townsend, Martin (2017) Field Guide to the Moths of Great Britain and Ireland. 3rd ed. London: Bloomsbury.

Websites

Atropos - migrant moth totals

GBIF - species distributions

Lepiforum

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 they still give useful pointers towards what's common and what's not.

[Note - this blog was updated on 26 July 2026 with additional text and images.]

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, it is found in North and South America and East Asia as well as Southern Europe. As with the previous two species, Pearly Underwing 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. Compared with Scarce Bordered Straw Bordered Straw looks 'cleaner', especially in its lighter forms. Note that there is an further confusion species - Eastern Bordered Straw: see the update added at the end of this blog post.

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 ...

Update - 26 July 2026. 

When I first wrote this post I omitted mention of an additional confusion species - the Eastern Bordered Straw Heliothis nubifera. This is because, first, it has been classed as extremely rare migrant to Britain and Ireland (only 39 records up to 2024 according to the Atropos website) and, second, I had never seen one so didn't have a photo to use. However, 2026 has been an extremely good year for Eastern Bordered Straw arrivals on our shores: I'm not sure what the current total is, but it must be well over 100 records. One finally turned up in my trap yesterday morning, so this is what it looks like:

Eastern Bordered Straw Heliothis nubifera - Dorset 24.7.26

While the kidney mark is similar in colour and shape to that of Bordered Straw, the rest of the forewing area is generally more richly marked, with brown blotches, better defined cross-lines and several black dots on the leading edge (costa).

As it happened, singles of both Bordered Straw and Scare Bordered Straw were also in trap, so I was able to picture all three together (below) - an uncommon sight for British moth recorders. 

Left to right: Scarce Bordered Straw, Eastern Border Straw and Bordered Straw - Dorset 24.7.26

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