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Fleas are parasites that live off the blood of their hosts. Although almost all mammals fall victim to one or more types of fleas, not all fleas bite all types of animals. The most common type of flea encountered in the United States is the cat flea (Ctenocephalides felis). Less common but more of a problem, the oriental rat flea (Xenopsylla cheopis) carries both bubonic plague and typhus. All share the same four basic stages in life.
First the Eggs
Fleas start out their lives as tiny eggs, so small that they’re practically invisible, only about 0.02 inches long. The female flea lays her eggs on a host animal to incubate, but many of them fall to the ground before they hatch, ending up in areas the animal frequents for sleeping and feeding. If conditions are favorable, which means warm and humid, the eggs will hatch into larvae after anywhere from two days to two weeks.
Flea larvae have no eyes and no legs, but they can move by wriggling and using the bristles that cover their bodies. During this stage they don’t feed on blood, but instead eat whatever they can find in their environment, including adult flea fecal matter, animal fecal matter and food that the host animal drops in the area. Larvae develop more quickly when temperatures are warm, but typically move into the next stage after about one to three weeks.
When the larvae have developed sufficiently, they wrap themselves in silk cocoons that totally envelop their bodies. The cocoon, or pupa, is virtually invisible and almost impossible to distinguish from bits of dirt or other debris. Inside the pupa the flea larva undergoes a transformation similar to what happens when a caterpillar transforms into a butterfly, except when this pupa opens after a week or two, a brown prickly flea emerges from within. If the environmental conditions aren’t right the pupa won’t hatch and can remain dormant up to a year, waiting for things to improve.
The final stage in a flea’s life is the adult stage, where she looks and acts like the fleas most people are familiar with. Fleas can sense hosts by both sight and body temperature, and will quickly jump on the first suitable animal or human that comes along. Although fleas can go for long periods without eating, it is only after feeding on blood that the female will lay her eggs on the host; she can produce thousands of eggs in her lifetime to complete the cycle.
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