Horsehair worms

How to identify horsehair worms

• Horsehair worms are long, measuring from several inches to over 14 inches.
• They are quite thin, ranging from 1/25 inch to 1/16 inch wide (1 mm to 1.5 mm) and are uniform in diameter from front to back.
• They vary in color from whitish to yellow/tan to brown/black.
• Horsehair worms are found on the ground or on plants, especially near water.

Behaviors

• Horsehair worms mate during spring, early summer or fall.
• Males coil around females in pools of fresh water or damp soil.
• It is common to see a number of worms to be intertwined, forming a loose ball during mating.
• Eggs are laid in a long, gelatinous string in fresh water.
• Once they hatch, immature horsehair worms try to infect a host.
• They can attack a wide variety of insects and related animals: grasshoppers, crickets, cockroaches, beetles, and katydids, as well as dragonflies, caddisflies, millipedes, centipedes, spiders, crustaceans, leeches, snails, slugs and other invertebrates.

Feeding

• It is not clear how immature horsehair worms infect hosts.
• When they infect their host, horsehair worms store up fats and food reserves.
• When the horsehair worm is mature and near water or damp soil, it emerges from its host.
• This process usually kills the host.
• Adults do not feed.

Where they live

• Horsehair worms are often seen in puddles and other pools of fresh water, swimming pools, water tanks and on plants.
• They are especially noticeable after rainfall.
• Horsehair worms may be found inside homes in toilets causing people to be concerned that it is a human parasite.

No control is necessary

Horsehair worms are harmless to people, pets and plants.

• They should be considered beneficial because they can be effective in controlling certain insects.
• No control is necessary for horsehair worms.