Many bees are parasitic, and regularly lay their eggs in the nests of other kinds of bees.

This case is more remarkable than that of the cuckoo; for these bees have not only had their instincts but their structure modified in accordance with their parasitic habits; for they do not possess the pollen-collecting apparatus which would have been indispensable if they had stored up food for their own young.

Some species of Sphegidae (wasp-like insects) are likewise parasitic; and M.