Some Male Fiddler Crabs Trap Females In Order To Mate With Them

Male banana fiddler crab (Uca mjoebergi) trying to woo a female.
The male crabs lure the females into their burrows before "coercing" them into mating. Tanya Detto/©Pat Backwell

How do you woo a member of the opposite sex? You could try putting on an irresistible display, or perhaps giving them a gift that they just can’t refuse. Just maybe, though, you could try trapping them in a confined space so that they have no other choice. That, it seems, is the method of choice for some male banana fiddler crabs.

The little crabs, native to the Australian beaches, live in burrows dug into the sand. In most cases, when a female is ready to choose a mate, she will scout out the local talent to look for a suitable burrow, visiting up to 20 before she makes her choice. The male crustaceans will usually then give their prospective mate a tour of his pad, leading the way into his abode. But this allows the females, if they so decide, the option to back out of the proceedings and get away, meaning the male is left without a mate.


The researchers looking into the success of the male crabs found that only 54 percent of the females who he had managed to coax in would be appropriately impressed by his beach-side pad and stay to mate. So some males have gone with an alternative method. Acting all chivalrous, they will instead let the females go first into their burrows, but before the female can make a decision, the male will quickly follow suit and trap her in.

Blocking her in his burrow, the dubious male will then “coerce” her into mating. This way, while a smaller percent of females will choose to enter his hole compared to those males who lead the way, a much larger proportion of them will lay eggs. In fact, the researchers found that a massive 90 percent of the females trapped in the burrows will lay, including those who might ordinarily have chosen someone else, making the crustaceans' technique actually quite successful.

“Mate-searching female fiddler crabs are fussy about the quality of a male's burrow, so they enter it to check its suitability as an incubation site before selecting the male as a mate,” explains Patricia Backwell, co-author of the study published in PLOS One, in a statement. “Some males trap the female inside the burrow, coercing them to mate.”

Why some males take to this shady habit is probably down to the intense competition the male fiddler crabs have with each other, meaning that it might pay off to be a bit pushy with the females, especially for those males who might not ordinarily be chosen as a mate.


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