Boxer Crabs Use Venomous Anemones To Hunt Prey, For Protection

Boxer crabs are found to have used their venomous anemones to feed themselves and to serve as protection against predators.

Scientists said these little crustacean are known to fight and eat while clutching their dangerous weapons, which are the sea anemones.

They studied the animal's relationship with the anemone and its involvement as a weapon during crab contests.

Findings of the study

The researchers selected a total of 12 pairs of crabs, which included six males and six females, and pitted them against each other while inside a tiny crustacean gladiator arena. The winner in the fight was the crab that retreated or fled the least.

They have observed and identified at least 15 behavioral acts during the crab contest, including five that were performed using anemones.

The behavioral acts of both opponents in each match were transcribed from video-taped encounters in a sequential order. Further their duration was recorded to the nearest second.

The motor activity was estimated for each crab through counting the number of lines crossed on the arena grid by the frontal margin of the carapace.

According to the experts, they had observed that the crabs utilized the anemones more for show rather than for contact. When the anemones touched the opponents, it seemed that it was done by accident.

"Ample evidence was accumulated in this study on the lack of anemone use during close contact. Although the crabs frequently used their anemones in intraspecific interactions during contests (i.e. Twitch, Extend, & Wave), they did so without touching their opponents. Even when extending one claw at close range, crabs invariably did so with the claw furthest away from the opponent," the study indicated.

There have been several hypotheses regarding the lack of use of anemones as a contact weapon during the contests, scientists said.

One of these was that the triactis producta are considered as highly toxic to Lybia edmondsoni. Crabs were observed to have avoided using anemones during intraspecific contests due to their supposed "high potential of severely harming both the winner and loser of a fight."

They pointed out that fights without using a dangerous alternative was also reported for poisonous snakes without even using their venom.

Another reason was that anemones constitute an inefficient weapon and were therefore not used during combat.

Food, extra oxygen

Meanwhile, the study also suggested some advantages for the use of anemone including reaching new sources of food and being supplied with extra oxygen due to the crab movements. On the other hand, some of the disadvantages might include being robbed of its food by the crab.

The Hawaiian boxer crab or pom pom crab (Lybia edmondsoni) are known to reside in the Hawaiian Islands. They usually feed on shrimp and squid, experts said.

These pom pom crabs are observed to grow to only around half an inch or 13 millimeters wide. Scientists said that its soft exoskeleton means its armor is pretty useless.

At present, scientists are still determining why the boxer crabs are clinging to the sea anemones. What the anemone gets out of it is still unknown in the scientific world.

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