Fleas
Order: Siphonaptera
Family: Pulicidae
Description
Fleas are wingless insects that have spines on the legs and body. These insects are small, measuring about 1.4-2 mm (1/18-1/13 inch) long and have flattened, red or brown bodies with piercing-sucking mouthparts for feeding on the blood of vertebrate animals. The hind legs of fleas are modified for jumping and they are sometimes mistaken for other small insects that hop such as springtails and flea beetles. The round or oval eggs of fleas are white and measure about 0.5 mm in length. Although rarely observed, flea larvae are worm-like tend to remain around host bedding or nesting sites. Newly hatched larvae are white but may become darker in color as they feed. When fully grown, larvae are about 4 mm (~1/6 inch) long and begin spinning silk to pupate. The sticky silk is often covered with dust, debris, and waste, which helps camouflage the pupa.
Given Colorado’s dry climate, fleas are rarely problematic. There are about 80 species of fleas inhabiting Colorado, and several species can bite humans. The most common is the human flea (Pulex irritans), which is most often associated with skunks, foxes, and coyotes. The human flea tends to prefer feeding on dog blood but will more readily feed on human blood than other flea species. Although uncommon in Colorado, the cat flea (Ctenocephalides felis) requires the blood of dogs or cats to reproduce and is the most important flea species in the United States. One species, Diamanus montanus, feeds on the blood of wild rodents such as squirrels and prairie dogs and is the primary vector of the bacteria that causes plague.
Quick Facts
- Fleas are found on all continents, including Antarctica, with approximately 80 flea species inhabiting Colorado.
- This pest requires high relative humidity to reproduce. Infestations are uncommon in Colorado due to the dry climate.
- Flea bites can trigger allergic reactions that cause itchiness and redness around the feeding site. Fleas can also transmit microbial pathogens to human and non-human hosts, including the plague.
- There are several indicators that a flea infestation may be present in the home. These include pets that continuously bite or scratch at the legs, belly, and back, and the presence of flea excrement that appears as dark spots on bedding or other resting areas frequently visited by pets.
- Effective management requires eradicating immature stages and adults through a combination of sanitary practices and insecticide applications.
Adult cat flea. Note the dark body color and spines on the legs. Image credit: Joseph Berger, Bugwood.org
Larva of the cat flea. Note the worm-like body shape. Image credit: Pest and Diseases Image Library, Bugwood.org
Life history and habits
These insects are opportunistic feeders that often feed on the blood of alternate hosts when their preferred host is not available. Attacks on humans tend to be most severe when infested animals die or are removed from the house, and bites on humans are usually confined to the ankles and lower legs. Most flea species are associated with mammalian hosts, and adult females typically require a blood meal to complete their reproductive development. To initiate feeding, adult fleas tend to wait for environmental cues such as sudden rises in temperature, humidity, or vibrations that indicate the presence of a host.
Of the flea species inhabiting Colorado, the cat flea is among the most well-studied. Adults of the cat flea begin laying eggs 8-24 hours after feeding and will usually die in one or two days after being removed from the host. A single cat flea female can lay up to 40-50 eggs per day and can continue reproducing for several months. Eggs of the cat flea require greater than 50% relative humidity to hatch, which limits their ability to reproduce in the dry climate of Colorado. However, infested pets may be transported from other areas with more favorable climates, such as Texas, California, and Florida. In such instances infestations may become established in areas of the home with sufficient humidity for flea reproduction.
Adults lay eggs in areas frequently associated with the animal host, and upon hatching the larvae begin feeding on the blood-rich waste of adult fleas, nearby flea eggs, or organic matter such as hair or feathers. Larvae tend to move away from sources of light and typically reach adulthood after several months, though the exact development time depends on temperature and relative humidity. Mature larvae migrate to soils, carpets, under furniture, or animal bedding to pupate. The pupae can remain dormant for over six months until a suitable host is available. It has been estimated that only 1-5% of the flea population is represented by adults on a host, with the remaining immature life stages present in the environment.
Flea bites
When feeding, fleas introduce saliva to the skin which can trigger allergic reactions such as flea allergic dermatitis. The feeding sites initially appear as small red spots surrounded by a red halo on the skin that can be isolated or grouped in clusters. The onset of itching can occur minutes after the bite was inflicted, and secondary infections can develop if the bites are scratched. Some individuals are extremely sensitive to flea bites, while others may experience very mild reactions.
Flea-borne diseases
The most well-known disease transmitted by fleas is the plague, which is caused by the bacteria Yersinia pestis. During the Middle Ages, it is estimated that this pathogen killed one third of the world’s population. In Colorado, D. montanus is the primary flea species that vectors the plague. Between 1957 and 1999, there were 45 confirmed cases of plague that resulted in the death of nine individuals in Colorado. Currently, about one case is reported per year. In addition to causing disease in humans, the pathogen disrupts the flea’s digestive system and causes the pest to seek and bite hosts more actively, further exacerbating the spread of the pathogen. Flea bites are the primary route of transmission, but the bacteria can also be introduced to a host when flea excrement is scratched into bites or wounds.
In addition to plague, fleas can transmit several other diseases to their hosts. For example, Dipylidium caninum is a tapeworm prevalent in dogs and cats throughout the world, and infections in humans have also been reported. Acanthocheilonema reconditum is a nematode that can infect humans and dogs and is transmitted by the cat flea, human flea, and the dog flea (Ctenocephalides canis). This parasite can cause ocular disease in humans and subcutaneous infections in animals. Flea-borne spotted fever (Rickettsia felis) is transmitted by the cat flea, with cats and dogs serving as major reservoir hosts. Infections of R. felis in humans causes illness like that of dengue. Fecal contamination of flea feeding sites or other wounds on the skin can transmit murine typhus (Rickettsia typhi) to humans and causes symptoms such as headaches, joint pain, abdominal pain, and confusion. Infections of Bartonella spp. cause various diseases, with cat scratch disease being the most common infection caused by these bacteria in humans. These bacteria are usually transmitted to humans via flea feces and cause inflammation of lymph nodes, followed by other conditions such as chronic ulcerative conjunctivitis.
Monitoring
When pets are infested with fleas, they tend to display signs of discomfort such as frequent scratching and biting of the legs, belly, and back. To scout for fleas, the fur of pets can be separated on the shoulder blades and base of the tail. Flea excrement can appear as small dark spots clustered on bedding. When cats are infested with fleas, excrement may also be found on tabletops, bookcases, and other raised surfaces.
Management
Managing established flea infestations can be challenging since a relatively small proportion of the flea population resides on the host. To eradicate an infestation, all life stages need to be eliminated through a combination of management approaches that include repeated deep cleaning of the environment and insecticide applications to eliminate immatures and adults, respectively. Regular vacuuming of carpets, blankets, and pet bedding will help remove immatures from the environment, and the use of insecticides formulated for flea control will help eliminate adult fleas on hosts. Some insecticides can also be applied to carpets and furniture to kill immature stages. However, these insecticides will not kill pupae, and multiple surface applications spaced several weeks apart are often necessary. Eradicating the flea population can take anywhere from several weeks to several months.
CSU Extension Fact Sheet
Download or view the CSU Extension’s PDF fact sheet for your reference.
References
CDC. 2017. Fleas. Centers for Disease Control and Prevention. Available https://www.cdc.gov/dpdx/fleas/index.html#:~:text=Pulex%20irritans%20is%20known%20as,The%20frons%20is%20broadly%2Drounded.
ECDC. 2021. Fleas (Siphonaptera) – Factsheet for health professionals. European Centre for Disease Prevention and Control. Available https://www.ecdc.europa.eu/en/all-topics-z/disease-vectors/facts/fleas-siphonaptera-factsheet-health-professionals#:~:text=The%20three%20most%20important%20flea,cat%20flea%20(Ctenocephalides%20felis)
Hodgson, E., J. Karren, and A. Roe. 2008. Fleas. Utah State University – Extension. Available https://digitalcommons.usu.edu/cgi/viewcontent.cgi?article=1903&context=extension_curall
Iannino, F., N. Sulli, A. Maitino, I. Pascucci, G. Pampiglione, and S. Salucci. 2017. Fleas of dog and cat: species, biology, and flea-borne diseases. Veterinaria Italiana. 53(4):227-288. Available https://pubmed.ncbi.nlm.nih.gov/29307121/
Rust, M., and M. Dryden. 1997. The Biology, Ecology, and Management of the Cat Flea. Annual Review of Entomology. 42: 451-473. Available https://annualreviews.org/doi/full/10.1146/annurev.ento.42.1.451
Shetlar, D., and J. Andon. 2012. Fleas. Ohio State University – Extension. Available https://ohioline.osu.edu/factsheet/HYG-2081-11