How to Tell if a Monarch is a Boy or Girl
Learning how to sex monarchs is especially helpful if you see a butterfly garden monarch and wonder if you should start searching for monarch butterfly eggs. I can guarantee with 100% certainty a male will leave no such gift.
Males are (slightly) larger than females, but butterflies (like people) come in many different sizes. Some caterpillars pupate appearing far too small, while others keep stuffing their little faces with milkweed ’til they’re ready to burst. I’ve seen giant monarch butterfly males and females. I’ve also seen both in mini-me form. So, if size doesn’t matter, how can you tell monarch males and females apart?
The male monarch butterfly has a black spot on each hind wing that is made up of specialized scales. In other butterflies, similar spots emit pheromones to attract females, but scientists are not sure what function these spots serve for monarch males.
These black dots are an excellent ‘male marker’ for sexing purposes.
The monarch female has noticeably thicker wing veins, which give her a darker appearance. The females hind wings are spotless…
When you compare them together, the differences become obvious. Unfortunately, most monarchs won’t be this cooperative in spreading their wings to let you get a close-up view. So how can you sex a close-winged butterfly?
Most of the time, you should be able to see part of the monarch male’s black dot bleeding through to the outside wing. In my experience, it’s pretty easy to see this outside mark on most males. Make a mental note of where this dot is located on the outside wing…you’ll have a much easier time finding it on future males.
Sex Monarchs by Caterpillar?
This is only possible through dissection.
Sex Monarchs by Chrysalis?
You can even tell the sex of a monarch by looking for some identifying marks at the top of the chrysalis. You won’t be able to see these subtle differences with the naked eye, but a digital camera with macro capability or a microscope makes it easy to see the differences:
The best way to get a good look at monarchs is by raising them. After adult butterflies hatch they need a couple hours to dry their wings before flight. This give you time to get up close and personal. Raised butterflies will typically allow you closer access after they’re released too…assuming you were a good butterfly parent!