Overzealous Male Frogs Practice a Practical Sort of Necrophilia

Both males and females still get to pass on their genes to the next generation, despite one of them being dead

Image: Axel Kwet

The males of the species Rhinella proboscidea, a small type of frog found in the Amazon, may be the most determined lovers on the planet. Overzealous, they form huge mating balls that sometimes suffocate females trapped in the middle, writes Ed Yong for National Geographic.

Although a potential mate may be dead, the males will not be deterred. In the end, they get what they’re after by squeezing the eggs out of the dead female’s body, then fertilizing them. Thiago Izzo, a scientist at the National Institute of Amazonian Research in Brazil, dubs this unique mating strategy “functional necrophilia.” (Pictured below—although, fair warning, it’s a little bit disturbing to see.)

A male having his way with a dead female by squeezing her eggs out. Photo: Izzo et al., Journal of Natural History

As Yong describes, hundreds of males gather during a two or three day mating window and await any female who might show up. When she does, the males pounce on her and begin wrestling for the right to do the deed. The female winds up at the bottom of this squirming ball of lust, often drowning in the affections of her would-be lovers.

Izzo has found several of these explosive balls of hormones and lust. In one ball, he discovered around one hundred males and twenty dead females; another revealed some fifty males and five females. All of the females, however, were missing their eggs. He solved this puzzle when he witnessed the necrophillic act first hand: a male grasped a dead female, squeezing her belly until eggs began popping out, which the male then scrambled to fertilize. Yong writes:

Izzo saw the same behaviour again and again. On one occasion, the male pushed his dead partner around the pond, “apparently to avoid other males”. The eggs that emerge are quickly fertilized—Izzo kept an eye on them and saw that they eventually developed into embryos.

For males, this act is clearly beneficial, since they succeed in passing on their genes. For the female, it’s a bit tougher to find a positive spin, but Izzo points out that, despite being dead, she still gets to pass on her genes to the next generation. It’s an interesting twist: usually in the animal kingdom, if anyone is going to be killing their mate, it will be male-gobbling cannibalistic females.

More from Smithsonian.com:

When Is the Right Time to Mate?  
For Female Golden Moles, Size Does Matter 

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