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The Selfish Reason Why Boxer Crabs Force Sea Anemones to Reproduce

The crabs are only thinking about themselves.

Boxer crabs are so named for their colorful "boxing gloves," that are actually living sea anemones.

They also look like cheerleading pom poms, so that's fun.


There are multiple benefits for the crabs to have these anemones chilling on their claws. According to NPR, the crab can "mop" up food particles with the anemones to eat. The stinging limbs protect the crabs from predators.

Here you can see a crab ward off a puffer fish with a stinging jab.

Giphy/Nature on PBS

However, scientists haven't quite figured out what's in it for the anemone to live with the crab. Although it can eat bits of the crab's own food, NPR reported that the crabs are very careful about controlling how much their pom poms eat.

For them, it's sort of like caring for a bonsai tree, where they carefully prune and trim it to keep it small.

If the food restriction seems a bit intense, you haven't seen anything yet.

It turns out that when a crab loses one of these anemone poms, all hell breaks loose.

Giphy/Nature on PBS

According to Popular Science, scientists studied boxer crabs and found that if they removed an anemone, the crab would immediately begin forcing the anemone to reproduce in order to replace the missing pom.

The University of Alaska Southeast reports that sea anemones can asexually reproduce by splitting lengthwise to create two halves of an anemone that each then can function as their own creature.

Popular Science reported that when the crabs are missing a pom pom, they spur this process along by gently tearing the anemones in two.

Then they'll again have two gloves.

Giphy/New Scientist

The scientists also found that if both their anemones were removed and they were placed in a tank with a crab that still had two, the pom-less crab would attack the other crab.

It would try to steal pieces of the anemone to start that reproduction process and have two anemones again.

NPR reported that the crabs would initiate these attacks even if the crab with anemones was much bigger.

Getting pieces of those anemones was just that important to them.

Giphy/New Scientist

According to Popular Science, it's the only known example of one animal forcing asexual reproduction in another species.

For these crabs, the anemones seem to be the ultimate security blanket.


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