Do blue crabs scratch their backs???

[kcschwabe]

So I was watching my blue crab doing something unusual today I noticed her upside-down on the one rock in her tank pumping her legs up and down (like Baloo from the jungle book) seemingly scratching her back... she is sexually mature and about 7 inches from point to point.. I’ve had her since she was smaller than a dime and never noticed this behavior before ..

Any feedback is welcome
I’ll try to get picks of her doing it on here soon here is just a random pick of her to give you an idea of size

 

[snorklr]

maybe getting ready to molt? i believe the shell starts to split along the rear seam