Of Cannibalism and Competition

Photo source: Sharyn East
Spiders offer up some of the best examples of sexual dimorphism, as seen here in the dramatic size difference between the female (Big Bessy) and the male (Tiny Tim).

Though I can't speak to the specific species here, I've learned that several taxa of orb weavers can have the male being as small as 10% of the female's size. Why the size difference? It comes down to two competing forces: sexual cannibalism and male-male competition.

The gist of it is that if you are small enough, you don't trigger the female's hunting instinct and you can get close enough to mate. However, if you're too small, a bigger male can crowd you out of the race. But then, if you're too big, you get eaten by your paramour.

The trick is to strike a happy medium. Not so big that you get eaten, but not so small that you can't muscle aside the competition.

This just gives me one more reason to be happy that I'm a human male. I did just fine with the male-male competition in capturing and keeping my wife's attention. But if I had run the risk of her eating me, that would have put a damper on my courtship technique (body armor doesn't accessorize well).