White worms and tiny critters in a shrimp tank: what they are and what to do
Shine a flashlight into a mature shrimp tank and you'll almost always find more than shrimp: thin white worms in the substrate, specks zipping across the glass, tiny bean-shaped critters on the plants. Almost all of them arrive on plants, moss, decor or in water from another tank, and most are harmless members of the clean-up crew. A sudden boom usually says more about how much food is going in than about a dangerous pest.
Identify what you're seeing
| What you see | Likely critter | Harmful to shrimp? | What to do |
|---|---|---|---|
| Thin white or reddish worms that wiggle in the substrate or whip in the water, often after feeding | Detritus worms (small annelid worms) | No | Feed less and siphon the substrate surface. Numbers fall when food does. |
| Very fine, short, clear-white worms that thrash in an S-shape on the glass | Nematodes (roundworms) | Free-living types, no | Same as detritus worms: less food, more cleaning. |
| Flat worms that glide smoothly, with a spade or triangular head and two eye spots | Planaria (flatworms) | Can be, especially for shrimplets and eggs | See planaria in a shrimp tank. |
| Tiny stalks with tentacles fixed to glass or plants, shrinking when touched | Hydra | Can catch shrimplets | See hydra in a shrimp tank. |
| Tiny bean- or seed-shaped critters that trundle over surfaces | Seed shrimp (ostracods) | No | Leave them, or cut feeding if numbers bother you. |
| White specks that jerk and hop through the water or on the glass | Copepods (cyclops and relatives) | No | Leave them. They're a normal part of a planted tank. |
| Small flattened, shrimp-like animals that swim on their side | Scuds (amphipods) | Usually not to adults; may eat plants and compete for food | Remove by hand or trap if they multiply. |
| Insect larvae with legs, a large jaw and a tapered body, often on plants | Dragonfly or damselfly nymphs | Yes, they hunt shrimp | Remove by hand with a net or tweezers. |
| Small white threads or bumps on a shrimp's head or rostrum | Possibly a parasite such as Scutariella | Can be | Get a close, clear photo and ask an experienced shrimp keeper or vendor before treating. |
Why there are suddenly so many
- Overfeeding. The most common cause by far. Uneaten food and powder that sinks into the substrate feed worms and copepods, and their numbers grow to match the food supply.
- Dirty substrate surface. Mulm, dead leaves and old food collect in corners and under decor.
- A new food or feeding style. Powders, blanched vegetables left too long and protein-rich foods are commonly linked to booms.
- Hitchhikers. New plants, moss and decor from other tanks are how most of these critters arrive in the first place.
- Few or no fish. In a shrimp-only tank, nothing eats them, so populations that would stay hidden in a community tank become visible.
How to cut the numbers back safely
- Feed less. Give only what your shrimp clear within a few hours, and remove leftovers. In a mature tank, shrimp find much of their food on surfaces. See best shrimp food.
- Use a feeding dish. A small glass dish keeps food in one place and lets you lift out what's left.
- Siphon the substrate surface lightly during your regular water change, and check the bucket for shrimplets before you pour it away.
- Rinse the filter sponge in old tank water if it's clogged with debris, never under the tap.
- Wait. With less food going in, populations usually shrink over a couple of weeks.
When to treat, and what to avoid
Harmless worms and copepods don't need a treatment, and the chemicals that kill them are a much bigger risk to shrimp than the critters themselves. Treatments only make sense for planaria or hydra that keep coming back after you cut feeding, and then only with a product that is widely described as shrimp-safe, used exactly as directed, with dead animals removed and a water change afterward. Many of these products also kill snails. Never use general aquarium dewormers, copper products or fish medicines in a shrimp tank without checking that they are invertebrate-safe. If you're not sure what you're looking at, a clear macro photo and a second opinion are cheaper than a lost colony.
Keep them out of the next tank
Most hitchhikers come in on plants. Rinsing new plants well, buying tissue-culture plants where you can, and keeping new plants in a separate container for a while before they go into the shrimp tank all reduce what you bring home.
Track it
A worm boom is easiest to explain when you can see what changed. Note feeding, water changes and substrate cleaning on the free Maintenance Schedule printable, and you'll usually find the boom started when feeding went up or cleaning slipped.
Frequently asked questions
Are white worms in my shrimp tank harmful?
Usually not. Thin white worms that wiggle are most often detritus worms or nematodes, which eat leftover food and waste and don't harm shrimp. Flat gliding worms, which may be planaria, are the ones to look at more closely.
How do I get rid of detritus worms in a shrimp tank?
Feed less, remove uneaten food, use a feeding dish and siphon the substrate surface during water changes. Their numbers usually fall within a couple of weeks once there is less food.
How do I tell planaria from other white worms?
Planaria are flat, glide smoothly like a slug and have a spade-shaped head with two eye spots. Detritus worms and nematodes are thin and round and wiggle or whip.
What are the tiny white bugs jumping on my aquarium glass?
Usually copepods, tiny crustaceans that hop through the water in jerks. They are harmless and common in planted shrimp tanks.
Do shrimp eat detritus worms?
Shrimp may pick at them, but they won't keep a large population down. Cutting back on food is what controls them.
Should I use a dewormer for white worms?
Not for harmless worms. Treatments carry more risk to shrimp than the worms do. They are only worth considering for persistent planaria or hydra, using a product widely described as shrimp-safe and following its directions exactly.
Sources: Shrimp Tank Hub's planaria, hydra, shrimp food and water change guides and their references; general freshwater invertebrate identification references; recurring owner reports (r/shrimptank and r/PlantedTank, 2024–2026).