How do you tell whether a butterfly or moth is a male or female?

    
Don Herbison-Evans
(donherbisonevans@outlook.com)
and
Stella Crossley

There are basically nine ways you may be able to tell a female moth or butterfly from a male.

1. ANTENNAE


male
showing feathery antennae.

female
showing threadlike antennae
Pholodes sinistraria showing difference in antennae

The antennae of Lepidoptera appear to be the main organs of smell. Many moth species fly only at night, or have flightless females, and so use pheromones for sexual attraction. Usually it is the female which emits the pheromone. which the males smell with the antennae. So the antennae of male moths of many species has a more feathery appearance than that of the female.

2. SEX BRANDS


male

female
Hesperilla idothea showing sex brands on the male forewings

The male and female butterflies of many species in HESPERIIDAE differ in that the males have a long mark near the middle of each forewing.

3. SIZE


male

female
Anthela acuta showing larger female

The abdomen of the female has to carry eggs, so in many species the abdomen of the female is fatter, and the wings bigger than those of the male.

4. FLIGHTLESS FEMALES


female

male
Teia anartoides showing flightless female and winged male

In the families PSYCHIDAE and LYMANTRIIDAE and subfamily LITHOSIINAE: the female of some species is flightless and has no wings at all.

5. DIMORPHISM


female

male
Papilio aegeus showing differing wing colouring of the sexes

Some species are dimorphic, so the female has a different pattern and coloration on the wings from that of the male.

6. TERRITORIAL BEHAVIOUR


Papilio anactus

With some butterflies and moths, for example Papilio anactus, the behaviour of the sexes is different. The males continually circle around their territory, which is typically 100 metres across, whereas the females just fly across the land haphazardly. So if you see the butterfly or moth come past regularly say every 15 minutes, it is a male. If you see it once and never again, it was a female.

7. EGGS



female Circopetes obtusata laying eggs

If you capture a moth or butterfly and keep it overnight, if it lays eggs it is definitely a female, and if it does not, then it could be a male.

8. ABDOMEN TIP



female Arthroschista hilaralis showing hair pencil on tip of abdomen

The tip of the abdomen of some moths has glands for dispersing pheromones, and these are sometimes accompanied by tufts of hair or eversible organs. Usually it is the females that emit the pheromones, and have a tuft of hairs for that purpose, but in some species the males have eversible hairs or organs which emit male pheromones.

9. DISSECTION

In some species, there is no obvious difference between the sexes, and one must resort to dissection of the tip of the abdomen to examine the genitalia under a microscope in order to work out the sex of a specimen.

Link to
Frequently Asked Questions about Caterpillars

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(updated 6 November 2012, 5 January 2014)