What Is the Strangest Mating Behavior in the Animal Kingdom?

The mating behavior of ceratioid anglerfish is unusual, to say the least. The male zeroes in on the much larger female when a bioluminescent appendage on her body, called a lure, sends out pheromones. It's love at first scent. The male proceeds to bite the female and doesn't let go. Eventually, his mouth fuses with her body, and they spend the rest of their lives attached -- with the female sharing her blood, and the male supplying sperm. It’s called sexual parasitism, or the deep sea version of “til death do us part.”

It's not you, it's me:

• There are more than 300 anglerfish species, but only 25 or so use sexual parasitism to reproduce. The little male looks like a different creature entirely, lacking the female’s enormous jaws and distinctive biological lure.
• Male ceratioid anglerfish don’t hunt; they only exist to attach to females. In the deep recesses of the sea, mates are scarce -- so only about one percent of males ever find a female. The rest starve to death and never reproduce.
• The male usually bites the female on her belly, and their tissues ultimately fuse together. The male’s eyes and fins atrophy, but he continues to breathe with his own gills.

Frequently Asked Questions

What is the strangest mating behavior in the animal kingdom?

One of the most bizarre mating behaviors is exhibited by the deep-sea anglerfish. The male anglerfish, significantly smaller than the female, attaches to her body, fusing their tissues and circulatory systems. Over time, the male becomes a parasitic appendage, providing sperm in exchange for nutrients from the female, a process unique in the animal kingdom.

How does the anglerfish's mating process work?

The male anglerfish, upon finding a female, bites into her belly and releases an enzyme that digests the skin of his mouth and her body, fusing them together. Their blood vessels join as one, and the male becomes dependent on the female for nutrients, while he provides sperm for fertilization when she releases eggs.

Are there any other animals with similar mating behaviors to the anglerfish?

While the anglerfish's mating behavior is unique, some other species exhibit extreme mating strategies. For example, the flatworms engage in "penis fencing," where two individuals use sharp penises to try to inseminate the other. However, none are known to permanently fuse bodies like anglerfish.

What evolutionary advantage does the anglerfish's mating behavior provide?

The anglerfish's mating strategy is advantageous in the deep sea's vast and sparsely populated environment. By becoming a permanent part of the female, the male ensures that whenever the female is ready to spawn, his sperm is immediately available, maximizing the chances of successful reproduction in an environment where encounters between individuals are rare.

How do male anglerfish find females in the deep sea?

Male anglerfish have developed highly sensitive olfactory organs that enable them to detect the pheromones released by females over great distances. This adaptation is crucial for locating mates in the dark, expansive depths of the ocean where visual cues are virtually nonexistent.

Does the female anglerfish mate with multiple males?

Yes, a single female anglerfish can mate with multiple males. Over her lifetime, several males may become attached to her body, each one providing sperm for different batches of eggs. This ensures genetic diversity and increases the likelihood of successful reproduction over the female's lifespan.