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How to identify it
- Adults are up to about 5 mm long, flattened from top to bottom and wingless, with six clawed legs.[1][2]
- The biting louse has a blunt head wider than its thorax, while the sucking louse has a pointed head narrower than its thorax. Both have a pair of prominent segmented antennae.[1]
- The biting louse is usually found on the upper sides of the body, while the sucking louse prefers the mane, tail and fetlocks.[1]
- The whitish eggs (nits) are fixed to the hairs, measure up to about 0.75 mm long and are easy to see with the naked eye, especially when there are many.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Horse bot fly eggs | Bot fly eggs are also stuck to horse hairs, but they sit toward the tip of the hair, while louse eggs sit near the base. A bot egg also holds a fly larva.[1] |
Where it lives
Biting and sucking lice occur on horses and other equids around the world, and Texas A&M lists the horse biting louse among the lice of livestock. In temperate regions such as Texas, louse numbers typically peak in winter or early spring and decline in summer, and in Canada infestations are more common and heavier in winter.[1][2]
Biology and life cycle
The whole life cycle happens on the horse. Females attach their eggs to hairs, three immature stages follow hatching, and the cycle takes a few weeks. Adults probably cannot survive off the horse for more than a few days.[1]
Biting lice feed mainly on skin debris, and sucking lice feed on blood.[1][2]
Lice usually pass from horse to horse by direct contact, though grooming equipment and tack can carry them too. Many horses carry lice without showing disease, and one infested horse in a group usually means all the horses in the group are infested.[1]
Some chewing lice of chickens can apparently infest horses housed with them.[1]
Young, old and sick animals are more susceptible to lice, and horses that are stressed in other ways may suffer more from them than healthy horses.[2][1]
Damage and signs
- Both kinds of lice cause itching. Horses rub and bite to relieve it, which leads to hair loss and skin damage until the coat can look moth-eaten.[1][2]
- The constant effort to relieve the itch can interfere with feeding and lead to poor condition, and the thinner coat gives less insulation in cold weather.[1]
- Heavy sucking-louse infestations can cause noticeable anemia from blood loss.[1]
Health risk
Horse lice are host-specific and not commonly passed to people, although they may occasionally be found on people.[1]
Control
Prevention
Control depends on finding and treating infested horses quickly, with particular attention to new arrivals joining a group.[1]
Sanitation
Clean tack, grooming equipment and other items that can carry lice between horses.[1]
Pesticides
In Canada, topical products containing carbaryl, pyrethrins, permethrin, or pyrethrins with permethrin are approved for lice on horses. Because the eggs survive treatment while the hatched lice do not, treatments need repeating, ideally three times at 10-day intervals. There are no good data on how well ivermectin or moxidectin work against horse lice.[1]
Texas A&M notes that most insecticides and formulations on the market work against lice, and its general advice for livestock is to treat at the end of fall, when treatment is needed, and repeat two weeks later.[2]
Common questions
- Why is my horse rubbing its mane and tail in winter?
- Lice are one cause. Louse numbers peak in winter or early spring, the sucking louse prefers the mane, tail and fetlocks, and both kinds of lice make horses rub and bite until hair falls out and the skin is damaged.[1][2]
- Can I get lice from my horse?
- Horse lice are host-specific and not commonly passed to people, although they may occasionally be found on people.[1]
- How do I tell louse eggs from bot eggs on my horse?
- Louse eggs sit near the base of the hair, and bot eggs sit toward the tip. A bot egg also contains a fly larva.[1]
Sources
- University of Saskatchewan, Western College of Veterinary Medicine, “Lice: Chewing: Werneckiella (Damalinia) equi; Sucking: Haematopinus asini (Learn About Parasites, June 2021).” wcvm.usask.ca/learnaboutparasites/parasites/lice-chewing-werneckiella-damalinia-equi-sucking-haematopinus-asini.php (accessed 2026-11-08)
- Texas A&M AgriLife Livestock and Veterinary Entomology, “Lice (Insects and Pests).” livestockvetento.tamu.edu/insectspests/lice/ (accessed 2026-11-08)
- iNaturalist, “Bovicola equi taxon page (order and family).” www.inaturalist.org/taxa/1396024 (accessed 2026-11-08)
- iNaturalist, “Haematopinus asini taxon page (order and family).” www.inaturalist.org/taxa/390148 (accessed 2026-11-08)