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Girl or Boy Butterfly?

It's not difficult to tell a boy butterfly from a girl butterfly. Having learned to tell the difference, one generalization that can be made (allowing for exceptions, of course) is that here in Berkeley CA the female Anise Swallowtails are generally larger than the males, at least in terms of wingspan.

Below is a pair of butterflies getting ready for their maiden voyages. The male is the smaller of the two, on the left.

Since wingspan is not an entirely reliable way to tell the sex of a butterfly, it's better to use the more air-tight approach: take a careful look at the butterfly's rear end.

Below is a close-up showing the tail-end of a female's abdomen:

There's a bit of a terminal point, but otherwise no fancy apparatus. And the yellow stripes go all the way to the tip.

By contrast, the male tail is elaborate---a pair of claspers for help in delivering sperm to the female:

And the yellow stripes do not go all the way to the tip, as the claspers have no yellow:

These details are easy to see if you wait for the butterfly to lift its wings enough to see the rear clearly. And bright light, such as sunlight, also helps make anatomical details clearer.

There is another picture of claspers in the section called Emergence.