Pool water may be the last place you'd expect to find worms of any sort, but they're actually quite common. Tiny red worm-type creatures -- bloodworms -- are the larvae of midges, a small insect resembling a mosquito. The bloodworm name comes from the blood-red color of these larvae.
How Bloodworms Get Into the Pool
Midges--the insects responsible for those tiny worms--lay eggs on top of the water surface. Stagnant and still water are common egg-laying sites, although swimming-pool water can be as well. In less than a week, the eggs hatch into tiny, wiggly creatures that turn darker red as they grow. They feed off of minuscule organic matter they find near the bottom, whether it is microorganisms in a mucky pond or in the dirt tracked into swimming pool. These larvae remain for two to seven weeks, then turn into pupae and work their way to the water surface after a few days, emerging as adult midges.
Treating the Pool Water for Bloodworms
If your pool has bloodworms, the free chlorine concentration is probably too low, because chlorine is lethal to these larvae. Rather than simply bringing the chlorine level up to the required 1 to 3 parts per million, it's best to treat the worms as an algae infestation and shock the pool by raising the chlorine concentration to 10 ppm or more. Before you do this, adjust the pH level to between 7.2 and 7.6. If the pH is too high, the shock treatment will be ineffective. If any worms survive the first shock treatment, repeat it. Vacuum the bottom of the pool to Waste after shocking to remove the dead larvae.
Removing Bloodworms From the Pool
Cleaning the pool regularly removes bloodworms, stray earthworms that may have fallen into the pool, and any other type of worm, insect or larvae present in the water.
- Vacuum the bottom of the pool daily to remove and help prevent infestations of bloodworms.
- Use the skimmer to remove all debris floating on and suspended in the water. This debris may include insect larvae and pupae, as well as plant matter that such creatures eat.
- Check the pool filter for collected debris and worms each day. Empty and rinse the filter cartridge with a garden hose before placing it back into the filter housing. Read your pool filter manual for specifics about your filter, because removal and cleaning methods may vary by model and brand.
- Look around the pool area for stagnant water, such as low spots on the pool deck where water can collect into puddles. Blot up the water, and clean the area.
- Keep the pool pump running eight hours a day or longer to keep the water circulating. The better it circulates, the less the chance for algae and bacterial issues. Water circulation also means the water continually gets cleaned by the pool filter, removing potential insect larva and eggs.
- Test the sanitizer and pH levels of the water several times per week to keep the water as clean and healthy for swimmers as possible. Rainwater, debris tracked in from swimmers or even the wind may add debris and pollutants to the water, making it less healthy. Add pool chemicals such as chlorine tablets or shock treatments as needed, following the recommendations on the package based on the water volume of your pool.
- Place a cover over the pool when you're not using it regularly. This helps keep out insects and foreign matter.
- Wipe down the inside walls of the pool with a pool brush or vacuum device to help prevent algae and bacterial growth -- insect larvae feed off such materials.
- Encourage pool guests to brush their feet off before entering the water to avoid tracking in dirt and grass. Cover muddy areas near the pool with bricks or stepping stones, and encourage swimmers not to step in dirty areas that may contain or lead to stagnant water.
- What's That Bug?: Bloodworms
- University of Wisconsin Extension: Wonderful, Wacky Water Critters
- Hong Kong Food and Environmental Hygiene Department: Guidelines on Prevention of Breeding of Blood Worms in Swimming Pools
- North Carolina State University Extension: Biology and Control of Non-Biting Aquatic Midges
- INYO Pools: Above Ground Pool Maintenance
Kathy Adams is an award-winning writer. She is an avid DIYer that is equally at home repurposing random objects into new, useful creations as she is at supporting community gardening efforts and writing about healthy alternatives to household chemicals. She's written numerous DIY articles for paint and decor companies, as well as for Black + Decker, Hunker, SFGate, Landlordology and others.