Lice (clade Phthiraptera), also known as “chewing lice” or “sucking lice”, are small crawling parasites that chew or suck on a host in order to feed. They are True Bugs and most closely related to barklice and booklice.
There are hundreds of species of lice which specialize on many different wild animals, for the purpose of this guide I am only including a few species that people are most likely to encounter.
– to 0.12″. Grey, turning reddish after sucking blood. Feed exclusively on human blood and will not attach to any other animal. Found on the head and will die within 24 hours without body heat. (photo © Human Head Louse ( ) Pediculus humanus capitis mike_h)
– to 0.14″. Closely related to Head Louse and looks identical. Lives in clothes, only moving to body to feed. Rare outside of situations where clothing is difficult to clean (decrepit prisons, refugee camps, or homeless populations). (photo © ) Human Body Louse ( Pediculus humanus corporis Janice Carr, CDC)
Pubic Louse (– to 0.08″. Shorter and rounder than head/body lice and with much thicker legs. Also known as “Crab Louse”, it is typically found in pubic hair though also can appear in course body hair, armpits, or eyebrows. (photo © ) Pthirus pubis Nuno Veríssimo P.)
– to 0.07″. A small flat louse. As a “chewing louse”, it scrapes skin and fluids off the skin rather than sucking blood. Found on domestic dogs as well as wild canids such as coyotes. (photo © Dog Chewing Louse ( ) Trichodectes canis Daniel Drew)
– to 0.1″. As a “sucking louse”, it inserts its more slender mouthparts into the animal in order to suck its blood. Found on domestic dogs -especially long-haired breeds- as well as wild canids such as coyotes. (photo © ) Dog Sucking Louse ( Linognathus setosus Rob Foster)
– to 0.24″. A large louse with slender head and a pointed end. Brown but becomes black when filled with blood. It is the only louse species found on swine. (photo © ) Pig Louse ( Haematopinus suis Marie Lou Legrand)
– to 0.14″. A chewing louse that concentrates around the vent, thighs, and breast of domestic birds including chickens, turkeys, peacocks, and ducks. The most common and most destructive of the chicken lice. (photo © Chicken Body Louse ( ) Menacanthus stramineus Kendra Abbott / Abbott Nature Photography)
Poultry Shaft Louse (– to 0.08″. A slightly smaller species of chewing louse. Live on the shafts of body feathers but also descends to the skin, feeding on feathers, dander, scales, and surface blood. (photo © ) Menopon gallinae Juan Cruzado Cortés)
Poultry Wing Louse (– to 0.09″. Darker with longer legs and much more slender body than other poultry lice. Found on the undersides of large wing and tail feathers, where it feeds on the feathers themselves as well as dander. (photo © ) Lipeurus caponis catchang)
Bed Bugs (family Cimicidae) are also parasites and true bugs, but are most closely related to assassin bugs. Unlike lice they tend to crawl away from their host after they’re finished biting in order to digest their meal.
– 0.2″. Small round reddish-brown bugs. Live in cracks in or near the bed, coming out at night to bite their human prey. Take 5-10 minutes to get a full meal, then retreat back to their hiding spot. (photo © Common Bed Bug ( ) Cimex lectularius Katja Schulz)
– 0.2″. Have longer hairs than the Common Bed Bug and 3rd antenna segment is just as long as 2nd. Primarily feed on bats but will sometimes move to humans sleeping in the same building. (photo © ) Western Bat Bug ( Cimex pilosellus Juan Cruzado Cortés)
Swallow Nest Bug – 0.2″. Found in the nests of cliff swallows and sometimes barn swallows. Where swallows build their nest on homes, on rare occasions these bugs have been known to move from the nests and bite humans. (photo © ) ( Oeciacus vicarius Sean McCann)
Fleas (order Siphonaptera) are tiny flightless jumping insects most closely related to scorpionflies. They feed by piercing and sucking blood, with different species focusing on different kinds of host.
Fleas are very small and don’t have obvious coloration, so they can only be identified under magnification. For that reason, most of the photos here are from prepared slides.
– to 0.1″. Has genal and pronotal “combs” (the comb-like bristles on the mouth and neck) and has 6 notches with protruding bristles on hind tibiae. The most common flea feeding on dogs and cats in the USA. Will bite humans as well. (photo © ( Cat Flea ) Ctenocephalides felis vuk)
Dog Flea ( – to 0.08″. Has genal and pronotal combs, front of head is more rounded than Cat Flea, has 8 notches with protruding bristles on hind tibiae. Feeds on mammals and is more common in Europe than in the USA. (photo © ) Ctenocephalides canis Katja ZSM)
– to 0.16″. Larger than dog/cat fleas and has no genal or pronotal combs. Also known as “House Flea” and can be found on numerous mammals and birds as well as humans. Originally from South America; guinea pigs may be its natural host. (photo © Human Flea ( ) Pulex irritans Katja ZSM)
Oriental Rat Flea (– to 0.15″. Has no genal or pronotal combs (the comb-like structures on the mouth and neck). Feeds on rodents, especially rats, and sometimes humans. Is famous as the main carrier of bubonic plague as well as typhus. (photo © Xenopsylla cheopis) Daniel Drew)
– Has no genal (mouth) comb but does have a pronotal (neck) comb. Feeds on wild rodents including mice, voles, and squirrels as well as rabbits. Is a known carrier of the plague bacterium. (photo © ( Rodent Flea ) Hoplopsyllus anomalus Gabor Racz)
Ground Squirrel Flea (– to 0.1″. Has no genal comb but does have a pronotal comb. Has very long mouthparts compared to other fleas. Feeds primarily on ground squirrels. Is a known carrier of the plague bacterium. (photo © Oropsylla montana) CDC)
– The genal (mouth) comb points horizontally rather than vertically. Often attacks around the ears. Most common on rabbits but will also bite dogs and cats. (photo © Rabbit Flea ( ) Spilopsyllus cuniculi British Fleas)
Giant Mountain Beaver Flea (– to 0.4″. The world’s largest flea, reaching nearly half an inch long. Has 46 spines in the pronotal comb as opposed to 36 in the closely related Hystrichopsylla schefferi) Hystrichopsylla gigas. Is only found on mountain beavers. (photo © Merrill Peterson via New York Times)
– to 0.1″. Has no genal comb but does have a pronotal comb. Feeds on chickens and other birds, living in the nest and only going onto the bird to feed for short durations.. (photo © ( Western Chicken Flea ) Ceratophyllus niger Spencer Entomological Collection, Beaty Biodiversity Museum, UBC)
– to 0.08″. Small and rotund, has no genal or pronotal comb. Serrated mouth allows it to anchor and remain embedded in a host, often in clusters. Mainly feeds on chickens but will also use mammals as hosts. (photo © ( Sticktight Flea ) Echidnophaga gallinacea Daniel Drew)
Sticktight Flea ( ) – embedded in human leg. This flea tends to target skin away hair or feathers, which on chickens means that it can be found around the eyes, comb, or between the toes. (photo © Echidnophaga gallinacea Erik Blosser)