Male and Female Monarchs
As usual, the male is on the top in this illustration. The finer venation is the most apparent difference here, to us but probably not to them.
There are distinguishing characteristics on the bodies of the adult monarchs that differentiate sex. Male monarchs have a distinct black spot on the dorsal surface of each hind wing. The black dot is the alar gland and is important in the mating process of monarchs. Males also have a lighter color and a finer wing venation that is a more subtle way of identifying sex.
Sexual reproduction of adult monarchs happens when the species recognizes a potential mate of the opposite sex by the flaunting of their colors. The male monarch chases the female monarch for a period of time where the female reacts with a flight pattern in accordance to whether or not she wants to mate. A zigzag course of flight signifies that she is trying to avoid the male while a vertical flight course implies that the female will consent to mating.
The alar glands, which are the small black pouches characteristic of the male, contain specialized scales that absorb sex pheromones produced by hair pencil glands at the tip of the male's abdomen. Males can brush the head of the female, her antennae, with his hair pencils and pacify her. Then he pounces on the female and carriers her to the ground pinning her down. The male then bends his abdomen in order to hold the female and transfer a package of sperm through short needle-like organs. The monarchs stay mated for 2-3 hours in the day and sometimes spend the night together if they mate at night. The process of copulation takes 2-14 hours where the female internally stores the sperm sac in her body releasing it to fertilize the eggs shortly before they are laid. Female monarchs can be mated up to 15 times and can lie up to approximately 400 eggs.