This week in the lab, we got to see two of our Atlantic rock crabs (Cancer irroratus) in the process of mating. To some, it looked like they were fighting, or like one was eating the other alive. In fact, they were in the “doubler” position, which looks as though the two are hugging each other.
In the pictures, the male crab is the larger of the two and the female is the smaller. Female crabs will molt right before or during mating, and this one did just that—an object came away from the pair that looked like a second crab. We realized that that was her shedded outer shell and that she
was now darker in color (Which you can see
in the second picture).
These two were in the doubler position only a few hours, but mating crabs can stay like this from five hours to three days. The female will store the male’s sperm under her abdomen, which will later attach to her eggs. She’ll then carry the fertilized eggs under her abdomen for about two weeks until they hatch.
Always something interesting to see in the Marine Lab!