Anoplura or Siphunculata - sucking lice (nits, crabs, body lice)

Fast facts about Anoplura/Siphunculata (sucking lice

Small, wingless parasites in both adult and nymphal stages of mammals
Head narrow and eyes reduced or absent
Antennae short
Piercing/sucking mouthparts, retracted into head when not feeding
Feeds solely on blood injecting an anticoagulant to allow free flow for feeding
Each leg ends in a strong claw well-developed for clinging to the host
Eggs are usually stuck on to the host's hair and hatch when the temperature is sufficiently high
500 species world wide, fewer than 50 in Europe, and 35 British species
Nearly all species of mammals are infected including seals and whales
The Anoplura are sometimes combined with the Mallophaga into one order called the Phthiraptera

Each species of louse has its own mammal species it feeds off of, and only rarely will one suck blood from another mammal species.

The Pediculidae family are parasitic on primates including man, and are apparently the only sucking lice to have functioning eyes.

Pediculus humanus, the human louse

On the right is Pediculus humanus, the human louse. It is usually found on the head gripping tightly on to the hair. There are two races of human louse, the head louse (Pediculus humanus capitis) and the body louse (Pediculus humanus corporis). Some experts say these should be split into two species, however they can interbreed. Both suck blood, and the body louse can transmit diseases, e.g. typhus and trench fever.

Outbreaks of body louse infestations usually only occur where hygiene is poor. Outbreaks of head lice are common in children even where there is good hygiene and frequent combing. For advice on getting rid of head lice see below. The human body louse has been found living and breeding on domestic pigs.

Head lice

Luckily the head louse does not transmit diseases. The head louse ranges in colour from dirty white to greyish black, and the colour of the adult depends on the colour of the hair of the host it was feeding on during its nymphal stages.

Each egg is cemented to the base of the hair near the scalp by the female, and will resist washing and combing with a normal comb. The cement is so strong that the shell of the egg usually remains fixed to the hair until it grows out or is cut. A female can lay up to 10 tubular eggs a day. The eggs are pearly white, 0.8 x 0.3 mm.

The nymphs are just a smaller version of the adults. The adults range from 2 - 6 mm, about the size of a sesame seed. They can reach maturity just eight days after hatching from an egg. There are 3 nymphal stages. During the first stage the insect is almost transparent until it takes a blood meal when it turns a shining red colour. Then as the blood darkens in the gut it turns a purple colour. The nymph feeds at least twice a day.

Feeding. Both nymphs and adults feed the same way. They press the front of the head against the skin of the host. Then curved teeth around the mouth fasten on to the skin, and the piercing stylets goes through the skin which has been lubricated by saliva.

Lifecycle. The egg hatches in 8 or 9 days, and will reach adulthood in less than 3 weeks. A female can lay up to 60 eggs, and it has been found that more than 80% of these go on to hatch. Head lice will die of starvation if they do not drink a blood meal for 55 hours. Transmission is though direct contact or sharing combs or brushes.

Personal experience When I was a child, once a week my mother washed my hair, sat me on the floor while she sat in a straight-backed chair and got out the nit-comb. For the next half hour she'd comb through my long hair till she was satisfied. I never had head lice.

Advice on treating head lice.

Only the presence of a live adult louse can prove you have head lice. Dried husks of eggs or skin moults of nymphs can only prove you have had contact or been in the same place as another person who has head lice. So no live lice means no infection.

Treating head lice

Firstly NO treatment works 100% on just one application, most will need to be repeated. There is resistance to all the chemical treatments, and this will vary with country and area within countries. So my advice is if you want to go down the chemical road buy two different types and use one one week and another the week after. The electric lice combs tend to clog up and stop working. For more details see below left.

A recent study by the London School for Hygiene and Tropical Medicine found that the old-fashioned hand combing method worked better than all the others, but it must be repeated. To make the combing easier you can apply conditioner or even olive oil, then rinse it out. You'll end up with lice-free, well-conditioned, glossy hair. Do this every 5 - 7 days until you can find no lice, then you are lice free. If outbreaks are common then it might be a good idea to do this regularly as a check.

Active ingredient in some chemical treatments

Malathion containing treatments. These are applied to dry hair and left on for at least eight hours. The treatment may cause stinging when the alcohol enters wounds made by scratching and lice.
Lindane containing treatments. Lindane is a neurotoxin, so be very, very careful and follow the instructions. It should be kept on wet hair for just four minutes.
Permethrin containing treatments. These should be left on the hair for just 10 minutes.
Pyrethrin containing treatments. These are usually applied as a shampoo to wet hair and left in for 10 minutes.

Some of the above treatments are unsuitable for pregnant women and babies, so do read the instructions very carefully.

Other non-insecticide shampoos are much safer, but will have limited use, so you will end up with cleaner lice.

Some things to remember.
A louse away from human hair will die within 55 hours
Eggs take 7 - 10 days to hatch
So one treatment/combing may get most of the adult lice, but to keep lice free you have to make sure there are no adult females to lay eggs and to get all the hatched lice from the eggs already there
The most common areas to find lice are behind the ears and at the back of the neck
A louse needs a blood meal every 3 - 6 hours

Phthirus pubis, human crab louse

Crab louse Phthirus pubis

Above is the crab louse Phthirus pubis. It has recently been discovered that the Crab louse is most closely related to the louse that lives on gorillas! Apparently they were one species around 3.3 million years ago.

The eggs are slightly smaller that the head and body louse eggs, and are glued firmly to the body hair. Eggs hatch in 7 - 8 days. There are 3 nymphal stages. The nymphs become adult in 13 - 17 days. It takes several hours for the insect to drink its blood meal. The adult dies if removed from the host for more than 24. It is found on pubic hair, eyelashes and eyebrows. Transmission is through sexual contact usually, but can occur via infested clothes or towels. It does not transmit disease, but the saliva of the louse causes skin irritation.

Body louse or clothing louse

Originally the body louse and head louse were a single species. The lifecycle is similar to that of the head louse, except that the eggs are glued to clothing - usually around seams - as well as body hair. The body louse female can lay over 100 eggs in her lifetime. Feeding usually occurs while the host is asleep. At other times the louse rests in the clothing. Body lice can withstand longer periods of starvation that head lice. Transmission is usually through infested clothing or bedding.

Louse bites are irritating and infection can enter wounds caused by scratching the bites. Where there are good hygiene facilities available lice are easily treated, and in healthy humans should cause no real health problems, though with schoolchildren outbreaks do seem to be occurring more frequently. Where hygiene facilities are poor, lice infestations can become debilitating through lack of sleep, and dangerous through transmission of diseases and wound infection. The body lose can carry the bacteria that cause typhus, trench fever and relapsing fever.

Linognathus setosus dog lice

On the left are Linognathus setosus which live on dogs. The male is 1.5 mm long and the female 2.0 mm long. They are usually found on the back, sides and around the base of the tail. They need a blood meal every two hours or so.

Their life cycle is around 2 - 3 weeks. They can be a vector of the dog tapeworm Diplydium caninum. They are found worldwide. Although Linognathus setosus will bite man and cause a minor irritation they cannot infest or live on man. However the dog tapeworm can live inside man, so if your dog has lice it might be a good idea to treat yourself for tapeworms if you suspect you have been infected.

Treatment. Getting rid of these lice is really easy. You can use FrontlineCombo, Advantix or any other treatment for bloodsuckers such as fleas and ticks. There is no need to get rid of the dog bedding as the lice will die in a few hours if they cannot have a blood meal. So a good shake outside or wash is all that is needed. You can also speed up the process and make your dog more comfortable by using a human nit comb to comb through the hair. A flea comb will get adult lice, but it will not get the eggs. Unfortunately the eggs have to hatch and feed before they die, so your dog will still scratch for a week or two.

There is another dog louse, a biting species called Trichodectes canis. It looks similar to Linognathus, but its head is broader. The treatment to get rid of it is the same though.