OC Butterfly Farm / Learn / How to tell if a Monarch Butterfly is male or female?

How do you tell if monarch butterfly is a male or a female?

How do you spot a monarch butterfly male? 
Look for the black spots on the bottom wings.
​If you see those spots, it's a male; no spots, it's a female.

What are those black spots? They are scent glands!

Male's black veins (those black lines on the wings) are also thinner than the female veins. 

As you can see, 100th monarch on OC Butterfly Farm was a Boy!