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Itch causing critters: In most cases, fleas are just a nuisance to their hosts, but some
people and some animals suffer allergic reactions to flea saliva
resulting in rashes. Flea bites generally result in the formation
 of a slightly raised, swollen, itching spot with a single puncture
point at the center. Fleas can also lead to hair loss as a result
of frequent scratching and biting by the animal, and can cause anemia
in extreme cases.
Spreaders... of disease: However, fleas can also act as a vector for disease. One possible
example of this was the bubonic plague, which may have been transmitted
between rodents and humans. Murine typhus (endemic typhus) fever,
and in some cases tapeworms can also be transmitted by fleas.
 Fleas pass through a complete life cycle consisting of egg, larva,
pupa and adult. Completion of the life cycle from egg to adult varies
from two weeks to eight months depending on the temperature, humidity,
food, and species. Normally after a blood meal, the female flea
lays about 15 to 20
eggs per day — up to 600 in its lifetime
— usually on the host (dogs, cats, rats, rabbits, mice, squirrels,
chipmunks, raccoons, opossums, foxes, chickens, humans, etc.). Eggs
loosely laid in the hair coat drop out almost anywhere, especially
where the host rests, sleeps or nests (rugs, carpets, upholstered
furniture, cat or dog boxes, kennels, sand boxes, etc.).
Eggs hatch between two days to two weeks into larvae found indoors
in and along floor cracks, crevices, along baseboards, under rug
edges and in furniture or beds. Outdoor development occurs in sandy
gravel soils (moist sand boxes, dirt crawlspace under the house,
under shrubs, etc.) where the host may rest or sleep. Sand and gravel
are very suitable for larval development which is the reason fleas
are erroneously called "sand fleas."
Larvae are blind, avoid light, pass through three larval instars
and take a week to several months to develop. Their food consists
of digested blood from adult flea feces, dead skin, hair, feathers,
and other organic debris; larvae do not suck blood. Pupae mature
to adulthood within a silken cocoon woven by the larva to which
pet hair, carpet fiber, dust, grass cuttings, and other debris adheres.
In about five to fourteen days, adult fleas emerge or may remain
resting in the cocoon until the detection of vibration (pet and
people movement), pressure (host animal lying down on them), heat,
noise, or carbon dioxide (meaning a potential blood source is near).
Most fleas overwinter in the larval or pupal stage with survival
and growth best during warm, moist winters and spring. "Flea
season" is traditionally at the end of summer and in the early
fall, but in warmer areas can last year round.
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