Males are generally (slightly) larger than females, but that can be deceiving. Just like people some are bigger, and some are smaller. Some caterpillars eat and eat and eat which makes them bigger when they pupate while some seem to just come in a mini. So, if size doesn’t matter, how can you tell monarch males and females apart?
You can’t tell what sex a monarch is when it is and egg.
You can’t tell what sex a monarch Caterpillar unless you dissect it.
You can tell what sex a monarch is when it is a 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 it’s easy to see the differences:
You can’t tell what sex a monarch is when it is and egg.
You can’t tell what sex a monarch Caterpillar unless you dissect it.
You can tell what sex a monarch is when it is a 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 it’s easy to see the differences:
You can tell for an adult monarch butterfly, and it is much easier! The easiest way is to look for the dot on the hindwing of the male. Harder to see but females tend to have a slightly darker coloration. The tip of the males abdomen is also different than the females (not visible in this image).
Sources:
Gomez, T. (2022, March 2). Male or female monarch butterflies difference? Butterfly Pictures... Monarch Butterfly Life. Retrieved December 26, 2022, from https://monarchbutterflylifecycle.com/blogs/raise/male-or-female-monarch-butterfly-pictures
Monarch madness. MONARCH MADNESS (Outdoor and Environmental Education). (n.d.). Retrieved December 26, 2022, from https://schools.wrdsb.ca/environmental-education/citizen-science/monarch-madness/