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Roughly 80 species of fleas can be found living in Colorado, which is among the largest number found in any state; however, flea infestations around the home and on pets are not nearly as common as in other areas of the United   States.  Colorado’s typically dry climate is not favorable for the immature stages of fleas.  Only a few species of fleas are involved in bites inflected on humans and domestic pets.  In general, fleas are small at only 1/13 – 1/18th of an inch and dark reddish-brown in color.  Fleas are blood feeders with specialized mouth parts to pierce skin and consume blood meals.  Hind legs are well-adapted for jumping, which can sometimes result in other insects being mistaken for fleas including springtails.  Adult fleas are flattened laterally and wingless.  Eggs are laid in areas frequently utilized by the host animal.  Larval stages of fleas are rarely seen and do not feed directly on animal blood, instead they feed on the blood-rich waste from adult fleas. Low humidity prolongs the developmental stages, sometimes for months at a time in order to reach the adult stage.  Full grown larvae move to small cracks and produce a cocoon covered in debris.  Emerging adults seek out blood meals from nearby hosts.

The most common flea associated with bites in humans in Colorado is the human flea.  Ironically, human fleas are typically associated with wildlife such as skunks, foxes and coyotes.  Bites to humans are usually encountered when wildlife dens are abandoned leaving the fleas to disburse in search of a new food source or when an overly curious person comes in close contact with a den site.  Fleas are then picked up and transported directly into homes on people and/or their pets.  Bites on humans normally appear as itchy, red spots that are surrounded by a red halo.  Clusters of bites are common and are commonly found at the edges of clothing.  While some people are fairly immune to flea bites and may exhibit little reaction, others may experience severe reactions.

One of the most significant fleas in much of the United States is the cat flea.  Thankfully, this is not the case in Colorado.  Cat fleas are capable of reproduction on both dogs and cats.  Pets moving in from out of state may harbor infestations causing cases of cat fleas within Colorado homes; however, these infestations rarely start on their own within the state.  Cat fleas require adequate humidity in order to become established within the home and overwinter.

A common concern among residents experiencing flea infestations is the possibility of contracting plague.  Fortunately, the flea most commonly associated with plague in Colorado is the rock squirrel flea associated with wild rodents.  Plague is a bacterial infection and while potentially life-threatening, is extremely rare in Colorado.  During a 43 year span from 1957 to 1999, only 45 confirmed cases of plague were found to have originated in Colorado.  The human flea, which is most commonly encountered in homes are not associated with transmitting plague in Colorado.

Treatment for flea infestations within a home will need to include treatment of pets, thorough vacuuming of cracks, crevices and areas the pets frequent.  Insecticidal treatment may also be necessary within the home.  Where wildlife dens are present and abandoned, treatment of those areas will also assist in control of the infestation.  Lawn areas where infestations have spread may need to be treated in order to prevent continued infestation of the interior of the home.