The purpose of this post is to point out some of the “structural” differences that can be used to aid in identification of moths. I’m by no means an “expert” in Lepidoptera, and I doubt there's anything in here that will be news to a professional Lepidopterist, but these are a few of the structural features that I’ve come to recognize as useful in moth ID, and I’ve found that a very large number of iNat misidentifications of moths could have been prevented by noting these features. I’ve compiled a “top 10” list of structures that can be used to immediately rule out possibilities when identifying moths. Moth ID is not as simple as “matching patterns” on the wings, as in many cases, wing patterns are variable within a species, while structures are more consistent. So here’s the list!
1- Antennae
When identifying an unfamiliar bird, noting the structure of the beak is like second-nature to an experienced birder. For moth ID, the antennae are just as vital. One of my go-to ID projects on iNat is “White Spring Moth” (Lomographa vestaliata). This moth has simple antennae in both males and females, and an easy way to pick out dozens of misidentifications when scrolling through White Spring Moth observations is to just look for pectinate antennae. Other all-white Geometrid moths often confused for White Spring Moths include Macaria pustularia:
And Cabera variolaria:
In both cases, male antennae are pectinate (“feathery”), eliminating White Spring Moth as an option for consideration.
In North America, Hepialidae can easily be recognized by the reduced antennae:
Male Pandemis have little notches along the outer margins of their antennae near the base that makes them instantly recognizable:
Male Phalaenostola metonalis and Phalaenostola eumelusalis have very different lengths to the pectens of the antenna that make them easy to separate with or without any scales left on the wings:
The list goes on and on and on… When trying to identify a moth, taking note of the antenna structure will allow for immediate dismissal of many potential species that have different antennae. This is the very first place I look when trying to make an identification.
2- Palps
The labial palps are extremely useful for moth identification. The labial palps stick out from the front of a moth’s face, and generally curve upwards to form little “horns” in front of the face, as seen clearly here:
Palps can be large and showy, such as in Acrolophus mortipennella:
The male (left) and female (right) in this species have wildly different shapes to their palps.
Pigritia have severely reduced palps, barely sticking out in front of the eyes:
The size, color, and shape of the palps can all be useful to note.
Ptycerata busckella has unmistakeable palps with extremely long forward-facing scale tufts:
Parapediasia has white tops to the palps, contrasting with darker sides, which makes it easy to distinguish from Fissicrambus, which had palps all one color:
Again, the list could go on forever… Comparing palps is a quick way to determine if an identification might be correct.
3- Thorax collar
The “collar” of the thorax is not very variable within most species, and can make some IDs easy. A good example is Orthodes majuscula, which has a big dark triangular spot right in the middle of the collar:
Even if all the scales are worn off the wings, this distinctive collar makes this species easy to recognize:
Mythimna oxygala and Leucania adjuta are frequently confused due to their similar wing patterns, but look at the difference in their collars:
One with a smooth, evenly colored tan collar, and one with a banded green-gray collar that contrasts strongly with the rest of the thorax.
Anicla illapsa and Anicla forbesi are distinguished by collars, as are several of the Euxoa species groups. It’s definitely something to take note of when performing an ID.
4- Costal fold
The “shoulders” of this Choristoneura rosaceana male illustrate what is meant by a “costal fold”, an extension of the forewing costa edge that curls over the costa:
Compare that to the costa of this Choristoneura parallela, which lacks a costal fold:
These two species have similar wing patterns, but that costal fold makes males easy to separate.
Similar species of Clepsis can also be separated by presence or absence of costal folds: virescana has it, while peritana doesn’t:
5- Scale structure
Moth scales come in a dramatic variety of shapes, and unsurprisingly, these shapes can often be used to separate species.
Eupsilia vinulenta, for example, has straight-edged scales between the reniform spot and the costa, while the nearly-identical Eupsilia cirripalea has scales in this region with long, stringy ends that rise up from the surface of the wing:
The wing patterns of the “red Eupsilia” species are variable and usually not helpful for IDs, but these scale shapes are consistent.
Another source of confusion with the “White Spring Moth” is Eudeilinia herminiata, a sometimes-spotted-sometimes-pure-white Drepanid. Look at the long hair-like scales on the thorax visible in this fresh specimen:
And compare to the thorax scale structure on this Lomographa:
Even without any wing pattern visible, the scales on the thorax are entirely different.
6- Foveae on wings
Moth wings are not always flat. Frequently, the topography of a moth’s wings includes distinctive structural features that can aid in identification. For example, Anavitrinella has a large raised fovea at the base of the male forewing, easily visible here:
Other genera often confused with Anavitrinella, like Iridopsis, lack this.
A moth like this, easily mistakable for Alypia, is clearly a male Androloma if one takes note of the swollen bit of the wing edge about two-thirds of the way out the costa:
A male Crocidophora might be mistakable for Hahncappsia or Ostrinia based on wing pattern alone, but look at this genus-defining wrinkly-ness of the forewing:
7- Hair pencils
Male moths of many species have pheromone-distributing structures called “hair pencils”. These tufts of scales increase surface area to promote the vaporization of pheromone compounds. The presence and location of hair pencils can assist in identification.
For example, male Coleotechnites differ from other related Litini by the presence of a massive hair pencil at the base of the hindwing. This is most visible on spread specimens, as seen here (the yellowish scales sticking out over the abdomen):
This male Chionodes is identifiable as Chionodes tarmes based mostly on the dark hair pencil visible over the base of the hindwing:
Chionodes hapsus has one too:
If you’re photographing moths in these groups, even a poor-quality photo of the moth in-flight showing the presence/absence of a hair pencil can be vital in obtaining an identification.
8- Raised scales
The genus that comes to mind when considering the presence or absence of “raised scales” on the forewings is Acrobasis. Different species-groups are defined largely on this feature. Here’s a good illustration of a species with raised scale “tufts” near the base of the forewings:
Compare to this one, with smooth wings lacking any such raised scales:
This Acleris also shows some raised scale tufts around the middle of the forewings.
Many misidentifications of Phycitinae on iNat could be prevented by taking note of raised scales on various species. Species like Myelopsis subtetricella have perfectly smooth wings with no raised scales, and species like Oneida lunulalis have such bold raised scale tufts that the common name features the word “tufted”.
9- Wing shape
Compare the shape of the wing in this “all-white Geometrid”:
To this one:
Or this one:
Again, wing patterns might look the same, but these are clearly three different species. One has a pointed hindwing, one has a concave apex to the forewing termen, and one has very rounded wings. If two moths have identical wing patterns but substantially different wing shapes, they’re probably different species.
Notice that the hindwing of this Gelechiid has an “extended” apex, coming to a distinct point:
Compare that to this Blastobasid, with an evenly rounded hindwing:
10- Body size
Here is one more “all-white” moth to compare to the three above:
This moth isn’t even in the same family as the previous three, as evidenced by the massively thick body.
The relative thickness of the thorax and the abdomen compared to the wings can easily separate some species. In general, Geometridae have dainty bodies, and Noctuids have thicker bodies, for example. Arctiines being misidentified as white Geometrids could be avoided by paying attention to this feature.
Honorable Mentions:
Among the other structural differences useful in moth IDs are:
-Eye size:
Compare these big peepers:
To these tiny ones:
Relative to the size of the moth, the eye size can differ dramatically between species, sometimes due to the moth’s diurnal/nocturnal habits.
-Genitalia:
Of course, dissecting a moth to reveal its genitalia structure is an identification game-changer, which opens up a whole new world of identification possibilities. This is rarely visible on live photos though.
-Wing venation
The pattern of veins on the wings was often used to define moth families/subfamilies/genera by early entomologists. These patterns are rarely visible on live photos.
-Leg structures
The spines on the legs, lengths of the legs, and color patterns of legs should not be ignored. Similar species like Catocala neogama and Catocala subnata can have very different densities of spines on their legs. Macaria promiscuata and Macaria aemulataria males are easily separated by promiscuata’s swollen leg segments. Dichomeris ventrellus and Dichomeris georgiella have different color patterns on their tarsal segments. Again, the list goes on and on…
Hopefully this post has been helpful in pointing out some of the features beyond wing patterns that can be used to identify moths. If one is in the habit of thinking about these features, then one is better-prepared to recognize “aberrant” color morphs of moths of common species, and to recognize unusual species with similar color patterns to common ones. Lepidoptera identification is a lot more than just “wing-pattern-matching”, and focusing on structural differences is a way to avoid some of the most common misidentifications that take place in this order.
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Thanks for this informative post!
Great points. Thanks for taking the time pull all these id tips together.
Thank you, Paul! Very informative!
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