Fleas are a parasite which feed on the blood of warm blooded animals, including humans. They pierce the skin, inject an anti-coagulant chemical into the host to prevent blood clotting and suck out the blood some passing straight through their rectum in order to lay their eggs. A flea bite can cause acute irritation, infection and transfer of other parasites, such as, tapeworms. Fleas often enter a building on dogs and cats, and are commonly deposited in carpeted areas, in the garden, yard and under the building. Flea eggs can take several weeks to more than 12 months to hatch - generally during hot humid weather causing an instant infestation of plague proportions.