Vitrealis : Starting to Identify Moths (part 2)

Introduction

I don't know about you, but my natural instinct when trying to identify something - be it moth, butterfly or bird - is to look at pictures in field guides or online. But with many groups of insect, this doesn't work. Differences between species, or even families, can be subtle or even invisible to a casual observer, making them difficult to illustrate by drawings or photographs. The normal identification method for many insects - from beetles to caddis flies - is therefore to use a key. This will set out a series of choices, allowing you (in an ideal world) to eventually reach an identification. Many insect keys require the use of lenses or microscopes, and in some cases dissection of genitalia.

Happily, moths (generally) are an exception. The good news is that most macro-moths and many micro-moths can be identified from obvious visual characters. As a result, most moth field guides do not contain detailed keys. Instead, they rely in the first instance on the user matching their specimen to an appropriate image before consulting the more detailed identification advice in their species accounts.

The bad news is that a beginner trying to identify a moth is faced with a bewildering variety of images, many of which - at first sight - look very similar to each other!

If you haven't already seen it then you may want to take a look at the first blog post of this series, which gives more detail about the identification resources that are out there (link: Identification Resources Blog Post). There are a lot and that list is growing. The purpose of the present post is to suggest a way of making sense of all of those pictures!

(Disclaimer: I'm only looking at macro-moths in the context of Britain and Ireland. Once you leave these shores, it gets even more interesting - and even more complicated!)

(Second disclaimer: This post is not intended to be comprehensive; the idea is to describe the families and sub-families that a beginner is most likely to come across.)

A Route Towards Identification

Obviously, you can trawl through the many hundreds of drawings or photographs one by one, which is time consuming and can be dispiriting. A better way to do it is to narrow your search - and the easiest first step along that route is to work out which family your moth belongs to.

You will search in vain for a simple key to macro-moth families. Mainly, this is because their formal definition is often based upon obscure characters: these include genitalia, the pattern on veins on their wings and features such as ocelli (additional lenses sited near to the main compound eye) and tympanal organs (which sense pressure or vibration). In addition, some characters only relate to caterpillars (larvae), which is hardly helpful when you're looking at an adult.

The other complication is that families have a nasty habit of changing as more information becomes available to the taxonomists. Hopefully, things have now settled down, although I wouldn't bet on it.

[As an aside, if you are looking for a book about general moth biology and evolution I can recommend David Lees and Alberto Zilli's Moths: Their biology, diversity and evolution which is published by the Natural History Museum. Reasonably priced, and nicely illustrated, it includes images of moths from the British Isles and around the world (NHBS bookshop link here)]

Macro-moths and Micro-moths

The distinction between 'macros' and 'micros' is so well established that it comes as a bit of a shock to learn that it has almost no scientific basis whatsoever. Apologies for a short detour into the world of taxonomy - the classification of life.

You can picture the evolution of moths and butterflies (which together make up the Order Lepidoptera) as a series of branches, as new forms have split off and diversified over millions of years. The older the split, the less that the modern day representatives of these branches are related to each other.

There are currently around 74 families of Lepidoptera (including the butterflies) on the British checklist (compiled by Agassiz, Heckford and Beaven in 2013, and regularly updated - link to the Natural History Museum data portal) . The checklist gives a two-part number to each species, the first part signifying its family, the second part being unique to that species. So the Vestal moth pictured at the start of this blog post has been given the number 70.038, meaning that it is the 38th species on the checklist in the Geometrid family (Geometridae) - family number 70.

In simple terms, the families that are classed as micro-moths were the earliest to split off from the 'main' evolutionary line of moths and butterflies (around 100-200 million years ago). You could call them 'primitive', although their surviving members are actually as modern as any other living moth. Most of the macro-moths appeared on the scene later (around 80-100 million years ago).

This evolutionary sequence is reflected in the checklist classification. Micro-moths, which comprise most of the moth families (around 50 out of 74), generally have the lower numbers, while macro-moths are generally higher.

However, to complicate things, a few of the more 'primitive' families are generally included with the macro-moths. The only reason for this is that they are large and easily observed. But they are only distantly related to the main group of macro-moths.

To bring this together, here is a list of the macro-moth families of Great Britain and Ireland, with their checklist number, scientific name, common name and the (approximate) number of resident species in our area - taken from the 3rd edition of Waring and Townsend (see my resources blog post for the detailed reference). This may look off-putting, but things are actually less complicated than they may first appear.

3. Hepialidae - Swift Moths (5 species)
50. Cossidae - Leopard and Goat Moths (3)
51. Sesiidae - Clearwings (14)
53. Limacodidae - Festoon and Triangle (2)
54. Zygaenidae - Forester and Burnet Moths (10)
65. Drepanidae - Hook-tips and Lutestrings (6)
66. Lasiocampidae - Eggar and Lappet Moths (10)
67. Endromidae - Kentish Glory (1) - but don't look for it in Kent!
68. Saturnidae - Emperor Moth (1)
69. Sphingidae - Hawk-moths (9 plus immigrants) - everyone's favourites
70. Geometridae - Geometrids (around 300)
71. Notodontidae - Prominents, Kittens and Processionaries (21)
72. Erebidae - Tussocks, Tigers, Footmen and the like (89 species) - a mixed bag
73. Noctuidae - Noctuids (around 370)
74. Nolidae - (14) - another mixed bag that can easily get confused with some micros

Several things jump out of this list.

First, and most importantly, the vast majority of macro-moths are in two large families - the Geometrids and Noctuids. Getting a feel for these two is an important step in learning to identify moths. It's a pity that these families don't have better common names. Geometrids (or geometer moths) are named for their caterpillars, some of which loop along as if they are making a measurement ("inchworms"). Elsewhere in the world, Noctuids are known as owlet moths, armyworms or cutworms, but none of these names are used here.

Second, the Hepialidae (Swift Moths) are real outliers in an evolutionary sense - family number 3 on the checklist. Their closest living relations are tiny micro-moths, not that you would know it from looking at them - for example this female Ghost Moth (below).

Ghost Moth (female) - an 'honorary' macro-moth (one of the Swift moths)

Third, you will see that there is a 'gap' between the Zygaenidae (54) and Drepanidae (65). This contains two important micro-moth families - the Pyralidae (61) and Crambidae (62) - which both include a few species that are large, common and conspicuous enough to be confused with macro-moths. Mother of Pearl is a good (and common) example - see below. The butterflies are also found in this 'gap' - they are families 56 to 61 in the Checklist. I've done a separate blog post on the differences (or not) between moths and butterflies - link here.

Mother of Pearl - a big "micro" moth (family: Crambidae)

Going Forward - First, check out the Big Two

So, you have found a macro-moth. How can you can assign it to a family?

The first job is to check whether it is a member of either of the 'Big Two' families, the Geometrids or the Noctuids. Given that these account for over two-thirds of our macro-moth species, including most of our commonest moths, there's a good chance that it will be.

(In Dorset, we publish an annual report that includes the Top Twenty most recorded moths for the year - downloadable free via this link. In 2022, all but three of these were in the 'Big Two' families.)

This post briefly runs through the moth families that you are most likely to encounter, giving typical examples from each one - starting with the 'Big Two'. The idea is that you should start to get a 'feel' for the characteristics of each family, which should help to narrow down your search for the correct species.

First, some typical Geometrids:

Typical Geometrid - Common White Wave

Grey Pug - another Geometrid (but pugs can be tricky!)

Mocha - a rarer, but lovely, Geometrid

Brimstone - an attractive and common Geometrid

Flame Carpet - the carpets are an important Geometrid group

Large Emerald - a stunning Geometrid

Early Thorn - a Geometrid that holds its wings vertically

While there's plenty of variety, it's also possible to observe a general theme. In Geometrids the wings rarely overlap and are usually held out flat like a basking butterfly. One group (the thorns) rest with their wings held vertically (or near-vertically); some other geometrids, like a carpets, will also sometimes close their wings above them. (This is annoying when you want to identify them.)

Turning to the other 'Big Two' family, here are some typical Noctuids. Most will lie flat with wings partly or wholly overlapped (a good pointer) but a few adopt a more upright (tent-like) position, like the Silver Y pictured a bit further down.

Typical Noctuid - Clouded Drab (a common Spring moth)

Large Yellow Underwing - one of the commonest Noctuids

Flame Shoulder - another common Noctuid.

Hebrew Character - a common Spring Noctuid

Coronet (Noctuid) - can be a common where you find Ash trees.

Silver Y - a Noctuid with an upright (tent-like) stance. A common migrant species.

Again, there is a clear general theme - Noctuids are usually stocky or chunky moths, with wings either overlapping or lying side-by-side (but not spread out like a butterfly). Most wings sit fairly flat, but some rest in a tent-like pose. But do note that some other families contain moths with these characteristics, for example the Ermines, which are found in our next family ...

Not the Big Two? Check the next biggest family.

So, what about the other families? I'll deal with the next largest first (the Erebidae) and then move onto some of the smaller - and perhaps more distinctive - families.

For me, the Erebidae doesn't hang together as a family. Its members appear very diverse, with no obvious linking visual theme. And indeed the taxonomists have found them to be problematic; anyone with a first edition of Waring and Townsend (2003) will discover that this family didn't even exist then!

Luckily, however, they break down into a few distinctive groups. Here are some typical ones: examples of the Snouts, Ermines, Tigers, Footmen and Underwings (excluding Yellow Underwings!), which all live within this family.

Snout - common and frequently seen (Erebidae).

Buff Ermine - a common member of the Erebidae. Like many Ermines, this is easily confused with the Noctuids.

Garden Tiger - my favourite of the Tigers (Erebidae) but sadly declining. Tigers are usually bright and colourful.

Dingy Footman - Footmen are a tricky group of the Erebidae

Red Underwing - sensational moths, but they don't like to hang around (Erebidae)

As I said, there is no obvious visual linking theme to this family, but each group (or sub-family) within the moths are generally distinctive.

Prominents - The Next Biggest Family

There may be only 21 species in the family, but some members of the Prominent & Kitten family (Notodontidae) will certainly turn up in your moth trap. Usually resting in a tent-like position like some of the Noctuids, they tend to appear more furry, and even more chunky, than most members of that family. Here are three typical examples:

Buff Tip - a crowd-pleasing twig-mimic (Notodontidae).

Pebble Prominent (Notodontidae).

Sallow Kitten (Notodontidae) - easily confused with Poplar Kitten.

Best of the Rest - Other Distinctive Families

Ignoring four families that are unlikely to turn up in your trap (but congratulations if they do!) - namely the Clearwings, Festoon/Triangle, Kentish Glory and Emperor Moth - that leaves us with seven more families that you are very likely to come across. Happily, most are pretty distinctive. Of these, three families can be easily identified: the Hawk-moths, the Eggars and the Burnet Moths. I'll start with these.

The Hawk-moths (family Sphingidae) are large and obvious. Even better, some are common. Here's two for starters:

Elephant Hawk-moth

Privet Hawk-moth - one of the biggest moths in Britain and Ireland

The Eggar moths (family Lasiocampidae) contain some of my favourite macro-moths. Like some other moths (for example most of the Notodontidae) the adults cannot feed. Most are large and particularly furry: here are two typical examples:

Oak Eggar (female)

Drinker - another Eggar moth

Although unlikely to appear in a light trap, the Burnet Moths (family Zygaenidae) are frequent and visible day-flyers in grassland and other open areas - especially sand dunes and flowery chalk grassland. Look for them on flower-heads. This is the most widely spread species in Britain and Ireland:

Six-spot Burnet Moth

Four more families to go! I've already introduced the Swift Moths (family Hepialidae) with the image of a Ghost Moth earlier on in this blog post. These hold their wings in a tent-like position like some of the Noctuids, but have a fairly consistent, rounded wing shape. Very often the abdomen pokes out beyond the back of the forewings. Here's another characteristic Swift Moth species that may well turn up in your light trap:

Orange Swift - a common Swift Moth

Only three species from the Goat and Leopard Moths (family Cossidae) are found in Britain and Ireland. All have long wings, which are also held in a tent-like resting position. Leopard Moth is most likely to appear in a moth trap, although it is absent from Ireland, Scotland and parts of Wales and Northern England. A lovely moth with distinctive black spots on a white background.

Leopard Moth (Cossidae)

The Hook-tip and Lutestring family (Drepanidae) is another family that has caused problems for the taxonomists. It is divided into two groups (strictly, sub-families) that look quite different from each other. However, within itself, each group has a fairly distinctive character.

The first group (the Hook-tips) generally hold their wings out flat like the Geometrids. The clue to their identification is in the name - look out for the hooked tip to their forewings (although, as we'll see later, not all hook-tipped moths are in this family!). Pebble Hook-tip (below) is a common and typical example of the Hook-tips.

Pebble Hook-tip (Drepanidae)

Having said that, there is one complete outlier in the Hook-tip sub-family - the Chinese Character. It is a common and fascinating little moth that mimics bird poo with great accuracy. It can be easy to miss.

Chinese Character - an unusual Hook-tip (Drepanidae)

The other sub-family of the Drepanidae are the Lutestrings. These look very like Noctuids, and I can't think of an easy way to separate them from that big family. However, there aren't very many of them and they are easily learned. First, a distinctive one; and then one that's a bit more confusing.

Peach Blossom - a distinctive member of the Drepanidae.

Common Lutestring - one of the Drepanidae that's easily confused with the Noctuids

And that leaves us with the Nolidae. Sitting after the Noctuids at the back of most field guides, these can get a bit overlooked. Like the Drepanidae, there is no obvious linking visual characteristic for the family as a whole, but also like that family, they are few in number and easily learned. Six of the family (all various kinds of Black Arches) do share a consistent 'look'. They are small, so there is a danger of confusing them with some micro-moths. Of these, Least Black Arches is the most widespread across Britain and Ireland, but it's still not common.

Least Black Arches (Nolidae) - not a micro-moth!

Very different, and rather more common (I'm happy to say) is the beautiful Green Silver-lines.

Green Silver-lines (Nolidae)

Whew! Well done if you've made it this far.

Finally ... what's in a name?

There's been a lot to get through in this blog post, but I'll leave with a quick word of warning about common (or vernacular) moth names. The message in a nutshell is as follows: common moth names can be inconsistent and confusing! Many relate to visual features that can be found across more than one moth family. Do not assume that a similar common name implies any sort of actual relationship.

For example:

Black Arches (family Erebidae) is not related to Least Black Arches, Kent Black Arches and the others in the Nolidae family.

Black Arches (Erebidae) - no relation to the Nolidae.

And the 'Arches' name applies to moths in other families as well - such as Green Arches (in the Noctuid family).

Green Arches - a Noctuid.

Beautiful Hook-tip (also family Erebidae - which has a lot to answer for!) is not a member of the Hook-tip family (Drepanidae), although it really looks like one.