by David Moore
Manager of Technical Services and Board Certified Entomologist
with contributions by Eric Smith, PhD, BCE

 

Most schools will start back soon. So, it probably won’t be long afterwards that you will once again be hearing about head lice. Head lice are a medical problem, not a pest control problem. So, it’s your responsibility to be able to recognize if your children become infested with head lice and if so, know what to do.

General Considerations

Three kinds of lice are found on people, head lice, body lice, and crab lice. Because these lice are strictly a medical problem, pest management professionals do not offer any control measures nor do they offer a control program for these lice. However, they can suggest sources of information that you can consult.

Recognition

Head and body lice are considered to be subspecies or different forms of the same louse, which look alike but behave differently. Metamorphosis is simple. This means that the young or nymphs are similar in appearance to the adults except for size.

Distinguishing characteristics:

  • About 1/8” (4 mm) long.
  • Their body is flattened top to bottom, but elongate in form.
  • Their head is only slightly narrower than thorax.
  • The abdominal segments lack lateral lobes.
  • They have 3 pairs of legs similar.
  • The tarsi (last segments of the leg) have 1 large claw adapted for grasping round hairs.
  • They look like light gray sesame seeds.
  • Behavioral separation of subspecies:
    • Head lice occur almost exclusively on the head and attach their eggs (nits) to hairs.
    • Body lice occur primarily in the clothing and move to adjacent body areas to feed.
    • They attach their eggs (nits) primarily to clothing fibers.

Biology

  • Head lice live continuously on the host.
  • On average, each female lays 6-7 oval eggs each day (lifetime total of 190-225) which are elongate in shape (about 1/32″ long by 1/64″ broad) and are fitted with a cap to facilitate nymphal emergence and respiration. They are pearly white when first laid, but change to brown before they hatch.
  • Each egg is individually securely cemented to a head hair near the scalp and is commonly called a nit. Eggs require high relative humidity and warmth in order to develop and hatch.
  • Eggs hatch in about 7-10 days.
  • There are 3 nymphal stages/instars that require 8-9 days.
  • The life cycle (egg to egg) requires about 3 weeks.
  • On average, adults live for about 32 days.
  • Head lice can survive no more than 48 hours off the host.

Habits

  • For all practical purposes, head lice occur only on the head because of their warmth and high humidity requirements.
  • They are most commonly found above the ears and on the back of the scalp, less often on the entire scalp.
  • They may rarely be found on hairs on other parts of the body such as in the eyelashes.
  • Head lice live continuously on the head area unless dislodged by scratching, hats, combs, hair brushes, towels, etc.
  • They are commonly transmitted by direct contact of two heads, or by combs, hairbrushes, or hats being shared, or by hats being temporarily stored in contact with other hats.

Diagnosis

  • The most important indication of a head louse problem is the presence of eggs or nits. This is because nits are more numerous than lice and are not active or easily removed.
  • A child scratching the back of the scalp or the nape of the neck is cause to suspect lice.
  • Scratching associated with lice is likely to lead to secondary infections which are more likely to cause itching than the bites themselves.

Incidence Of Head Lice

  • The socio economic group or income level of the family has little to do with who gets infested.
  • Lead louse problems are particularly common among younger school children.
  • Caucasian (white) children are more likely to have head lice problems than Afro- American (black) children.
  • Girls are more likely to be infested than boys, up to 5% more likely.
  • Cutting or wearing shorter hair does not prevent or eliminate an infestation, but does make inspection easier.

Control Of Head Lice

  • Head louse control is a medical problem, period!
  • This is because head lice spend essentially all of their time on the human head unless accidentally dislodged.
  • For all practical purposes, they cannot survive for more than 48 hours off their host.
  • Lice that are easily dislodged or drop from their host are usually feeble and unlikely to infest a new host.
  • Note: For these 3 reasons, residual pesticide treatments are unlikely to be of any control value.

Control on the human host

  • The typical therapy for head louse infestations consists of prescribed shampoo treatments or over-the-counter preparations containing insecticides. Follow the instructions on the product label.
    • Two or more treatments are required because not all eggs/nits are killed by the first application. A second treatment is usually prescribed for 7-10 days later which allows time for any viable eggs to hatch. This is because the egg/nit stage is resistant to penetration by insecticides.
  • The non-insecticidal control method. The use of a louse comb to remove lice and nits is becoming the preferred control method. The reasons are:
    • Insecticide-resistant lice (up to 100%) are being encountered with increasing frequency, especially to the pyrethrin/pyrethroid products.
    • The misuse or inappropriate use of over-the-counter and prescription materials can cause problems; under application promotes development of resistance, and over application may cause problems for the person being treated.
    • The increased concern about the toxicity to children of these insecticides, and
    • The concern about the resultant water pollution when these products/materials are used.
  • Because of secondary infections of the scalp from scratching, antibiotic therapy may also be required.
  • Non-infested family members or schoolmates should be examined regularly for lice, but preventative treatments are not recommended.
  • Nits located more than 1½″ (3-4 cm) from the scalp are most likely either dead or have hatched.

Required Sanitation

  • Hot cycle washing and hot drying (125° for 20 minutes once dry) of clothing, bedding, and towels used by infested individuals, and those of individuals who sleep in the same bed with an infested person.
  • Non-infested family members and schoolmates should not share towels, combs, hairbrushes, hats, and similar items with infested persons.
  • Requirements typically unknown by school personnel and the public but essential for a successful control program.
  • Children have significantly higher rates of infestation in schools in which lockers are shared as opposed to schools where individual lockers are the norm.
  • Children in schools with assigned wall hooks for their clothing have significantly lower head lice problems than in schools where hooks are unassigned.
  • It is almost a certainty that head lice will not survive in an empty school building from the close of classes on Friday until they reconvene on Monday morning.
  • A sanitation strategy is required for the short-term storage of hats, scarves, and coats to reduce the transfer of head lice. As examples, the following are suggested:
    • Children should not share combs, hairbrushes, hats, or clothing.
    • Children’s hats should be tucked into coat sleeves, with coats stored individually.
    • Children’s sleeping mats and/or towels should be stored individually and sent home for regular washings.
    • School-provided napping mats, gym mats, or headgear should be wiped clean or vacuumed after each use.
    • Carpeted areas should be vacuumed frequently, daily if there is an infestation problem.

General & Additional Information

The National Pediculosis Association and others recommend:

  • First, be sure of the identification. Many things look like lice and/or nits and infestations are commonly over diagnosed.
  • That children infested with head lice should be sent home until they have been successfully treated with a pediculicide (louse killer) and/or all lice, lice eggs (nits), and egg cases have been removed from the head. Metal louse/nit combs work best to remove lice, nits, and empty egg cases, but the process is time consuming.
  • That parents should be educated as to their responsibilities in eliminating head lice. Note: Both the University of Nebraska Cooperative Extension Service ( www.LanCo@unl.edu) , and the Harvard School of Public Health (www.hsph.harvard.edu/headlice and then click on HEAD LICE RESOURCES: Head Lice) have excellent detailed and illustrated web sites for parents and educators. The CDC also has an excellent website (www.cdc.gov).

Verification of infestation

  • Any suspect insects and/or nits should be collected into and preserved in a jar/vial containing 70% rubbing (isopropyl) alcohol.
  • They can then be taken to an entomologist for verification of their identity.