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.