A Flea is a common small wingless insect. Fleas, being external parasites, live by hematophagy off the blood of mammals and birds that they live on. There is several different species of fleas, with the most well known being: - Cat Flea - Dog Flea - Northern Rat Flea - Oriental Rat Flea It is rare that flea's become damaging to their host; in most cases they are just nuisances. There can however become a problem when the host suffers an allergic reaction to the flea saliva. Spots where fleas bite are normally visible by a slightly raised and itchy swolled spot, that will have a single puncture at the center. It is important to note that opposite to what I said above, fleas can transmit diseases. This is a rare scenario, but does happen, and an example is the bubonic plague where the disease was transferred between rodents and humans. If that is not bad enough Murine typhus fever and even some cases of tapeworms can be transmitted by fleas. Fleas are busy little insects and will pass through a complete life cycle, egg to adult, in as short as two weeks to as long as eight months, depending on environment conditions. Generally after a blood meal a female flea will lay eggs, about 15 per day, and up to about 600 in its whole lifetime. The eggs are generally layed on the host, and will often times drop off the host. These Flea eggs take between 2 days to 2 weeks to hatch.