The little red worms found in pools are called bloodworms, and they're the larvae of a tiny midge belonging to the Chironomid family. Midges resemble mosquitoes, but they're smaller and they can't bite. Unlike mosquitoes, which suck blood, most adult midges don't even eat. There are around 2,000 midge species in North America, according to the New College of Florida.
Bloodworms are thin "worms" with segmented bodies and they grow to be a little more than an inch in length. In addition, they have a pair of fleshy stub-like limbs at the front and the back ends of their bodies. Their bright red colour comes from the presence of haemoglobin in their blood. The haemoglobin lets them breathe in water that contains low amounts of oxygen. Bloodworms eat algae and microscopic animals.
Bloodworms are considered beneficial in their natural environment because they're a food source for fish and insects. In addition, they help clean ponds and other water bodies where they live by eating organic debris. Their presence indicates poor water quality, which can serve as a useful warning but, when midges lay eggs in swimming pools, they become a nuisance for swimmers. Although the larvae are harmless and don't transmit disease, people don't like to see them in the water.
Inspect your pool, and the area around your pool, every week to reduce the number of bloodworms that hatch in the water. Don't forget to check underneath damaged floor tiles and artificial turf. Repair damaged tiles and fill in cracks where water can collect and stagnate. Don't let water accumulate in empty soda cans or other containers. Clean and disinfect pool equipment, floors, steps, handrails and other areas with a solution of 1 part household bleach to 99 parts water. Use a pool cover when your swimming pool isn't in use and make sure it's properly sealed. Don't let water accumulate on top of the pool cover. Adult midges are attracted to lights. Avoid turning on unnecessary lights around your pool when midges are active in the evening.
Remove eggs and larvae from your swimming pool by running your skimmer and filter every day. Use a larvicide to kill the bloodworms, but make sure the larvicide is approved for use in a swimming pool. Larvicides that are approved for homeowners to use can be purchased from garden nurseries, hardware stores and pet shops.