Sexing Lepidoptera: Conversation and references

In response to @mamestraconfigurata 's comment about not being able to sex ADULT lepis without dissection, I respectfully disagree.

For nocturnal lepis this is very easy as long as the antennae are visible (moths often fold the antennae under the wings, the unco-operative little so-and-sos ;-).

The females have filiform or pectinate antennae, and the males have bipectinate antennae. This is because the females give off the pheromones, and the males locate them using their (sometimes rather magnificent) antennae.

A couple of examples:

Streblote sp. (Lasiocampidae) LEFT: female RIGHT: male

Drepanogynis cnephaeogramma (Geometridae) TOP: female BOTTOM: male
(Note: the wing colours are not gender-specific, this is a highly variable species. It’s all in the antennae!)

There is a fascinating article by Hermann Staude about species of moths choosing to become diurnal, and the changes in who attracts who.

Nocturnal moths have the females sending the signals and the males with larger antennae to detect said signals. Whereas those moths that are fully diurnal have the males sending out the pheromones and the females coming to them.

Hermann shows how the switch to diurnalism is slow (evolutionarily speaking) because of the problem of detecting female pheromones during the day, so that some species have day-flying females, but the males are still nocturnal so that they can detect the females. An example is Speckle Orange Acanthovalva focularia - only males are attracted to light at night, and only females are caught in butterfly traps set out during the day.

Fascinating read - download it for free Metamorphosis 19 pg 35.

So, antennal characteristics are probably not as useful for diurnal moths and butterflies.

And now I’ve gone way off topic for which I apologise. This stuff is all so thrilling that I sometimes lose the plot ;-D

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I admit that I had forgotten about that aspect! However, with some moths (like Nocuidae) it is not always cut and dried. Sometimes the difference is minimal. And on another minor point, it is the females that produce the pheromones, which the males pick up (hence the more ‘fuzzy’ antennae). I will look at your reference - I had never though about that aspect of things.
Many thanks!

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I’m going to go way off topic here - I read that paper, and sort of agree with it’s premise (A question is why would one species become diurnal out of a whole related group?). But a thought popped into my mind - why are there no recorded predators or parasites which use the moth pheromones (night or day) to find prey? Or even make a similar pheromone? I mean, they are likely to get two or more for one! The fascinating thing about science is how it can raise questions!!!

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I think this paper will interest you
Structure of the pheromone communication channel in moths

It includes a small section on predators & parasitoids. The section is small because the recorded instances are few.

There is also a fun paper about male moths collecting Pyrrolizidine alkaloids (PAs) to please females. Michael Boppré’s paper in Metamorphosis can be downloaded here:
‘Drug addicted’ insects in Africa

This is now so far off-topic that perhaps we should just PM?

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bird dropping spiders (Celaenia?) release the female pheromone of certain moth species to attract the males…

Thanks for both of those references!

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There are a lot of butterflies, at least in my neck of the woods that are identifiable as male or female.
Couple of examples, this is a male monarch I posted recently. The “milkweed” butterflies, the males have two black spots(one each in the black mark closest to the body) that release pheromones.
https://www.inaturalist.org/observations/33215818
Here is julia heliconia photo(my photo, just have never made an observation for it) but quite clearly a difference between male and female.
julia11

of the 650ish species of NZ moth illustrated at:
https://www.landcareresearch.co.nz/resources/identification/animals/large-moths/image-gallery
I would estimate 95% can be easily sexed from photographs that show clearly antennae, wings and/or posterior of abdomen. For each species which of those three things is more likely to help will be different from others.

I hate to disagree, but I went through a number of the Noctuid images, and while some show “fuzzy” antennae, generally the males and female antennae look the same. Keep in mind that I am only referring to Noctuidae. Other groups, including Butterflies, I have little experience with, The differences between the sexes are generally are sometimes more pronounced.

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antennae are just one of the characters that can be used to differentiate sex.

Pasiphila%20testulata%20%23M2%20A_SDB83LHT
Pasiphila%20testulata%20%23F2%20A_SDB83LHT

the male (top image) has a little crescent shaped window, whereas the female doesn’t. This character is easily seen on any photo showing the wing surface, and given they rest with wings flat, it is almost always visible.

but yes… noctuids are usually more difficult than other families

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Yes, noctuids are difficult! And there are so many of them! It is true that antenna form is not terribly useful in this family :-(

Unless the sexes are dimorphic, the only other (non-destructive) way to distinguish them is by the number of bristles on the frenulum ** - males have 1, females have more than 1. The frenulum is not usually visible in photos though.

The above info was kindly supplied by Hermann Staude.

Or one could watch a moth for a while I guess - if it lays eggs it’s a female, if it doesn’t then it’s inconclusive ;-)

Not a big issue in the great scheme of things I don’t think :-D But good to know!

** Frenulum - a row of bristles along the leading (front) edge of the hind wing of moths and also in some Hymenoptera such as bees and wasps. The frenulum connects the hindwing and forewing and makes the two wings act as a single surface during flight.

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Hermann also says many geometrids and most Pyraloidea don’t have sexually dimorphic antennae. Hey ho :-)

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It’s unfortunate that my preferred group is Noctuidae! I guess it has coloured my perspective on moths.