Crayfish are sometimes referred to as crawdads or crawfish. Like other crustaceans, they possess hard outer shells and claws that protect them from predators. Female and male crustaceans have differences in a few areas, such as size, but in almost every other aspect they are similar. The number of crayfish species is considerably large, and they vary in size. Check the size. According to the book "Small Scale Crayfish Farming," male crayfish are longer with larger claws. Examine the abdomen. Female crayfish have larger abdomens than the males. This is not surprising since the female lays the eggs. According to the authors of the book "Crayfish," some species of female crayfish lay as many as 800 eggs at a time. Compare the legs. Also called swimmerets, the legs on female crayfish are more developed than those on the male crayfish. The first two pairs of legs on the mature male crayfish are long and tubular.