Black Worms in Toilet: What They Are and How to Get Rid of Them

Seeing tiny black worms wriggling in your toilet bowl is unsettling, but it’s a common household issue with a straightforward explanation. These worms aren’t coming from your plumbing and they aren’t inside your body. They’re usually drain fly larvae—a sign that there’s standing water, organic buildup, or mild bacteria growth in or around the toilet.

Here’s what they are, why they appear, and the safest way to get rid of them for good.

What Are the Black Worms in Your Toilet?

Most of the time, the “worms” you’re seeing are drain fly larvae. They’re small (about 1/8 to 1/4 inch), dark, and often seen crawling near the waterline, under the rim, or in stagnant areas.

Why drain fly larvae show up:

• They thrive in damp, dark, organic-rich areas

• Toilets left unused for days or weeks become ideal breeding zones

• Build-up under the rim, in the overflow passage, or inside the siphon jet gives them food

• Slow-draining toilets or old wax rings can create moisture pockets

Drain flies themselves are harmless, but their presence signals that something inside the toilet or nearby needs cleaning or repair.

Less Common Possibilities

While drain fly larvae are the most common, other insects can end up in toilets:

Moth Fly Larvae

Similar to drain fly larvae but appear more segmented.

Earthworms

These show up only if:

• There's a crack in the sewer line

• The toilet seal is damaged

• Moist soil or groundwater is entering the line

If you see longer, slim, red or brown worms, call a plumber for evaluation.

Bloodworms (Red midge fly larvae)

These prefer standing water in outdoor locations and rarely appear in indoor toilets unless the bathroom is extremely humid or unused for long periods.

Are Black Worms Dangerous?

The worms themselves aren’t harmful to humans. They don’t bite or spread disease. But the conditions that allow them to grow—moisture, bacteria, organic sludge—should be addressed for hygiene and to prevent re-infestation.

How to Get Rid of Black Worms in the Toilet

1. Flush the toilet repeatedly

This removes any larvae floating in the bowl.

2. Scrub thoroughly under the rim

Use:

• A stiff toilet brush

• A disinfecting cleaner

• Special attention to the siphon jet holes

Most larvae hide where normal cleaning doesn’t reach.

3. Clean the toilet tank

If you rarely open the tank, bacteria and algae can form there.

Steps:

• Turn off the water supply

• Flush to empty the tank

• Scrub with a brush and disinfectant

• Refill and flush again

4. Pour a drain-safe enzyme cleaner into the toilet

Enzyme cleaners break down organic material inside plumbing where larvae feed. Use them once a week for a few weeks.

Avoid bleach as your only solution; it kills surface bacteria but doesn’t remove the buildup they live on.

5. Check for slow drainage

A toilet that drains slowly keeps more residue in the pipes, creating a breeding ground.

A plumber may need to:

• Clear buildup

• Remove partial blockages

• Check for wax-ring leaks

6. Reduce moisture in the bathroom

Good ventilation helps prevent future infestations. Run an exhaust fan or open windows after showers.

How to Prevent Black Worms From Returning

Once you remove the larvae, prevention keeps them from coming back.

• Clean the bowl and rim weekly

• Add enzyme cleaner monthly

• Fix slow drains immediately

• Avoid leaving the toilet unused for long periods

• Repair wax rings or seals if you notice sewer smells or movement at the base

Drain flies breed quickly, so consistency matters.

When to Call a Plumber

Professional help is needed when:

• Worms keep returning after cleaning

• The toilet drains slowly or gurgles

• You notice sewer odors

• You see earthworms (indicates a crack or break in a sewer line)

• The toilet is old and may have hidden buildup or a failing wax ring

A licensed plumber can inspect the drain, clear blockages, and repair structural issues that home cleaning can’t fix. If you need an easy way to find reliable plumbers, marketplaces like DreamDen help you quickly connect with qualified professionals in your area. DreamDen also includes electricians, masons, interior designers, and other home improvement pros so your entire project list stays in one place.

Final Answer: Why Are There Black Worms in Your Toilet?

Black worms in a toilet are almost always drain fly larvae, living in hidden organic buildup. They’re not dangerous, but they indicate cleaning or minor plumbing issues. A deep clean, enzyme treatment, and better moisture control usually solve the problem. Persistent infestations or unusual worms call for professional inspection.