by Whit Gibbons

May 31, 2015

Q: Fleas, flies and mosquitoes have started to become a problem around our house. How long do these loathsome creatures live?

A: An adult flea may live on a dog or cat from several days to more than three weeks, sucking blood from your pet the entire time. So-called dog fleas and cat fleas are different species, but both can live on either animal. Neither will hesitate to bite a human if that's where they land.

Controlling fleas has been a problem since dogs and cats were first domesticated, and a variety of toxic chemicals have been used in their control for decades. Unfortunately, fleas evolve like all other organisms, and those that survive one type of toxic control substance soon produce offspring that are invulnerable to it. Hence, the original flea collars became obsolete as a new generation of resistant fleas was produced. Proper flea control involves breaking the life cycle, which includes blood-sucking females that drop an egg an hour into carpets or bedding as well as the larvae and pupae that live from several days to a couple of weeks before emerging as fleas ready to pounce on the first warm body. By one estimate, in a house with fleas, more than half are in the preadult stage. As if a flea bite were not a big enough nuisance in itself, fleas are known to transmit the bacterium that causes bubonic plague.

Common houseflies have always been a nuisance during the summertime, pestering people in recreational areas and on backyard decks. Our annoyance with the persistence of flies landing on the edges of drinking glasses or bottles is presumably a natural response as these creatures have been indicted as carriers of diseases as severe as typhoid, cholera and certain forms of dysentery. A female housefly lays more than a hundred eggs, as many as three or more times, on rotting vegetation or other unsavory matter. Dry dog food that has been left several days may even be a place for egg laying.

Upon hatching, the eggs of the housefly go through larval and pupal stages (maggots) before emerging as adult flies after a period of 10 days to two weeks. This is a good time to destroy potential nesting areas, before the adults emerge. A female fly takes about two weeks to begin laying eggs, which means an individual fly might be around to bother us for far longer than we would like. Eliminating potential egg-laying sites is a major step in helping reduce future outbreaks of flies. Rolling up a section of your newspaper to use as a fly swatter won't kill many flies, but you'll have the satisfaction of knowing you've shortened a two-week visit for some individuals.

Mosquitoes go through a basic life cycle from egg to larva to pupa before becoming adults. Mosquito larvae and pupae are the "wigglers" seen in standing water that can be as negligible as that collected in a magnolia leaf lying on the ground, the rim of an upturned bucket or a low spot in a house gutter. Some kinds of mosquitoes lay their eggs on damp or even dry soil in depressions that later fill with water, stimulating the eggs to hatch. The aquatic stages last for a few days to a week or more, depending on the species. Adult mosquitoes can live for days or weeks. Only the females suck blood; this is part of the reproductive cycle. The males are benign creatures, and some feed on nectar. Surely no one needs a lesson in the threats mosquitoes pose, including malaria, yellow fever, and West Nile virus.

Even without the potential dangers to health caused by fleas, flies and mosquitoes, the plain nuisance of their presence is reason enough not to want them around. As I have said before, ridding ourselves of ones that are bothering us in some way seems all right to me. Most ecologists I know would agree.

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