Fleas are insects from the Siphonaptera order. They are wingless, with mouthparts adapted for piercing skin and sucking blood. Fleas are external parasites living by hematophagy of the blood of mammals and birds. Some flea species are cat flea. Dog flea. Human flea.northern rat flea. Fleas go through a complete life cycle from egg.larva,pupa,adult they must feed on blood before they are capable of reproduction. There populations are evenly distributed with 50 per cent eggs 35 per cent larva 10 per cent pupae and 5 per cent adults. Eggs take about two days to two weeks to hatch. The larva pupate within two to three weeks after three larval stages,after another week or two the adult flea is fully developed and ready to emerge from its cocoon.there total life span can be about one year but up to three in ideal circumstances.