Order Phthiraptera (Lice)

Phthiraptera. A human body louse. Note the flattened, wingless body, and single tarsal claw. Modified from Imms 1934.

Introduction

Phthiraptera (theer-AP-tera) are small (0.5 mm – 8 mm long), wingless, blind, parasitic insects. True lice have simple metamorphosis, the female glues eggs to feathers or hairs (or cloths in the case of humans), immatures look similar to adults, and they have three instars before becoming adults. The true lice are generally divided into two groups, the chewing lice, which affect mostly birds, and the sucking lice, which affect mammals including humans.

Collection and Preservation

Due to their small size, photography of lice is difficult. If you suspect you have found a louse, it is best to keep the specimen so it can be identified. Preserve the specimens in alcohol (80% ethyl alcohol is best, but rubbing alcohol will do). Try to collect as many specimens as you can to ensure you have an identifiable adult. Take the specimens to the appropriate specialist to be properly identified.

Chewing Lice

Chewing lice (suborders Amblycera and Ischnocera) are mostly found on birds, but some members will parasitize mammals. They have visible antennae (sometimes recessed in a grove), mouthparts used for chewing, and lack eyes and ocular points. Chewing lice feed on feathers, hair, dermal materials, and fluid or blood from minor abrasions.

Sucking Lice

Sucking lice (suborders Rhynchophthirina and Anoplura) feed directly on the blood of the host and can transmit diseases. Rhynchophthirina is only found on elephants and African pigs. Anoplura do not have visible mouthparts and lack palps. They lack eyes, but possess ocular points. The antennae are usually 5 segmented and the thoracic segments are fused. Each leg has a single tarsal segment tipped with a single curved claw that is used for clasping the hair of the host.

Most lice are very host specific, so lice living on squirrels or birds will NOT attack humans even if they are brought into the house. Three species of lice (all within Anoplura) infest humans.

Head Lice

Taxonomy

Domain	Eukarya
Kingdom	Animalia
Phylum	Arthropoda
Subphylum	Hexapoda
Class	Insecta
Subclass	Pterygota
Infraclass	Neoptera
Order	Phthiraptera
Suborder	Anoplura
Family	Pediculidae
Genus	Pediculus
Species	Pediculus humanus

Scientific Name

Pediculus humanus capitis

Common Name

head lice

Head lice (Pediculus capitis De Geer) are about 3 mm (1/8 in) in length and are white with dark markings on the side. They are most commonly found on head, in hair above the ears, and on the back of the scalp. Eggs are tan and glued on the base of hairs. Females lay up to 10 eggs in 24 hours and a total of 80 to 140 eggs over their lifetime. Nymphs emerge from eggs in 7 to 9 days. There are three nymphal stages and they complete development in 8 to 12 days. The frequency of infestation is greatest on children.

Body Lice

Body lice (Pediculus humanus Linnaeus) are about 4 mm (1/7 in) in length and gray. Unlike other lice they prefer to remain in clothing hiding in seams, will hold onto the fabric while feeding, and glue their eggs to fabric, not hair. Females lay 5 to 8 eggs per day and may lay 100 – 150 eggs over a lifetime. Nymphs emerge from eggs in 7 to 21 days depending on temperature. Nymphs go through three instars and become adults in about 11 days, and the entire life cycle takes about 3 weeks. Body lice will die within about 10 days if unable to feed on a host.

Body lice are the only lice that transmit disease in humans. They vector typhus, trench fever, and relapsing fever. The microorganisms causing these diseases are introduced into the host when infected louse feces is scratched into the host's wounds. These diseases are associated with unclean and crowded conditions.

Pubic Lice

Public Lice or Crab lice (Phthirus pubis (Linnaeus)) have a crab like whitish body and reddish legs. They are about 1.6 mm (1/16 in) in length. These lice are generally found on hair in the pubic region (most common), but may also occur on hair in armpits, beards, or eyebrows. Eggs are glued to hairs. Females lay three eggs per day, and the life cycle takes 20 to 25 days. Pubic lice do not transmit diseases. They die in 24 hours after removal from the host.

Summary and References

Eighteen families and ~941 species of Phthiraptera are recorded from North America north of Mexico. Of those only the three species above will attack humans. Mallis (1997) and Triplehorn and Johnson (2005) are good general references for information about this order.

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Print References

First Detector Entomology Training Project