Water louse (Asellus aquaticus) care guide

Group
Other invertebrates
Other names
Pond slater, Water hoglouse, Aquatic sowbug, Cress bug, Oniscus aquaticus
Family
Asellidae
Origin
Native to Britain; across Europe from Ireland and Iberia to Turkey and western Russia, and north to Scandinavia
Water
freshwater
Maximum size
2 cm
Temperature
4–20°C
pH
6.5–8.5
Hardness
6–15 dGH, 3–8 dKH
Minimum tank
10 litres
Care level
beginner
Temperament
peaceful
Lifespan
1–2 years

Care

The water louse or pond slater is a small freshwater isopod, a relative of woodlice, found in rivers, streams, ponds and ditches. It grows to about 2 cm, though many adults are half that, with a flat grey-brown body about three times as long as wide, long antennae and seven pairs of legs. Two white spots on the back of the head help tell it from the smaller Proasellus meridianus. Males are larger than females. Native species: it is native to Britain, so it needs a coldwater (unheated) tank or pond. Do not collect it from the wild where that is not allowed, for example on protected sites. Tank set-up: easy in any unheated tank with stones, wood and plenty of dead leaves to hide under. It avoids strongly acidic water. It is tolerant of a range of pollutants, which is why it is used as a water-quality indicator, but it still does best in clean, oxygenated water. Role: a harmless, useful detritivore that eats dead leaves, fungi, algae and debris, helping to break down waste in ponds and coldwater tanks. It is also a good live food for coldwater fish. It may nibble soft plant shoots. Copper: copper-based medicines and some plant fertilisers are toxic to shrimp, snails and most invertebrates. Never dose them in a tank holding this animal, check the label of any treatment or fertiliser, and use a separate hospital tank for fish. Sources: Wikipedia (en.wikipedia.org/wiki/Asellusaquaticus). Checked October 2026.

Diet

Detritivore: dead and decaying leaves, fungi, algae, biofilm and soft plant shoots. Add oak, beech or alder leaves and the odd sinking pellet or blanched vegetable.

Breeding

Breeds all year when the water is warm enough and stops in cold conditions. A male carries and guards a female for 6–8 days, and they mate in a short window around her moult. The female carries eggs in a brood pouch under her body, and the young leave as tiny copies of the adult (direct development, no larvae). Maturity takes a few months in warm water or up to two years in cold water, and there can be several generations a year. Breeds readily in tanks and ponds.

Compatibility and tank mates

Peaceful and harmless to fish, shrimp and snails. Most coldwater fish will eat it. It may graze soft plant shoots but rarely does damage in a tank with plenty of leaf litter.

Last updated 8 October 2026. Community-edited care guide on Aquatic-Auctions.

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