Many animals have differences between males and females, but some species have EXTREME differences!

The elephant seal male and female are very different sizes:

The huia female (bottom) had a beak very different from the male (top):

The eclectus parrot male (left) looks totally different from the female (right):

The triplewart seadevil, an anglerfish. On the drawing, you can see the male labeled in very small letters:

The female argonaut, also called the paper nautilus, makes a delicate see-through shell:

The male argonaut has no shell and is much smaller than the female (photo by Ryo Minemizu):

Lamprologus callipterus males are much larger than females:

The female green spoonworm. Male not pictured because he's only a few millimeters long:

Show transcript:

Welcome to Strange Animals Podcast. I’m your host, Kate Shaw.

I still have a lot of listener suggestions to get to, and don’t worry, I’ve got them all on the list. But I have other topics I want to cover first, like this week’s subject of extreme sexual dimorphism!

Sexual dimorphism is when the male of a species looks much different from the female. Not all animals show sexual dimorphism and most that do have relatively small differences. A lot of male birds are more brightly colored than females, for instance. The peacock is probably the most spectacular example, with the males having a brightly colored, iridescent fan of a tail to show off for the hens, which are mostly brown and gray, although they do have iridescent green neck feathers too.

But eclectus parrot males and females don’t even look like the same bird. The male is mostly green while the female is mostly red and purple. In fact, the first scientists to see them thought they were different species.

Males of some species are larger than females, while females of some species are larger than males. In the case of the elephant seal, the males are much larger than females. We talked about the northern elephant seal briefly last week, but only how big the male is. A male southern elephant seal can grow up to 20 feet long, or 6 meters, and can weigh up to 8,800 pounds, or 4,000 kg. The female usually only grows to about half that length and weight. The difference in this case is because males are fiercely territorial and fight each other, so a big male has an advantage over other males and reproduces more often. But the female doesn’t fight, so her smaller size means she doesn’t need to eat as much.

Another major size difference happens in spiders, but in this case the female is far larger than the male in many species. For instance, the body of the female western black widow spider, which lives throughout western North America, is about half an inch in length, or 16 mm, although of course that doesn’t count the legs. But the male is only half this length at most. Not only that, the male is skinny where the female has a large rounded abdomen, and the male is brown with pale markings, while the female is glossy black with a red hourglass marking on her abdomen. Female western widows can be dangerous since their venom is strong enough to kill many animals, although usually their bite is only painful and not deadly to humans and other mammals. But while the male does have venom, he can only inject a tiny amount with a bite so isn’t considered very dangerous in comparison.

The reason many male spiders are so much smaller than females is that the females of some species of spider will eat the male after or even during mating if she’s hungry. The smaller the male is, the less of a meal he would be and the less likely the female will bother to eat him. In the case of the western black widow, the male prefers to mate with females who are in good condition. In other words, he doesn’t want to spend time with a hungry female.

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