When is the Water Slater most available to trout?

January–December, typically All day. It picks up from about 3°C, peaks around 12°C and tails off by 23°C.

What flies imitate the Water Slater?

Gold Ribbed Hare's Ear, Pheasant Tail Nymph, typically on a #14 hook.

How big is the Water Slater?

Adult stage: 10–16mm. That matches a #14 hook.

Crustacean · Aquatic invertebrate

Water Slater

Asellus aquaticus

Size

10–16mm

Hook size

#14

Always there

No hatch and no season — this is in the water every month of the year, so it's always a fair bet when nothing is showing on top.

How fish feed on it

No hatch to wait for and no season to miss — shrimp and hoglice are in the weed and the gravel every day of the year, and trout eat them steadily whether anything is happening on the surface or not. Fish them slow and close to the bottom. On a cold day when nothing is moving, this is very often what the fish are actually doing.

Flies that imitate this

Gold Ribbed Hare's Ear

Pheasant Tail Nymph

Ecology

Rivers & stillwaterTolerates poor water

Where you'll find this

British IslesPresent
IberiaPresent
The AlpsPresent
ScandinaviaPresent
Continental EuropePresent
Atlantic fringePresent
North America — WestPresent
North America — EastPresent
East AsiaPresent
New ZealandPresent
PatagoniaPresent

Present throughout

Identification

Asellus aquaticus is a freshwater crustacean resembling a woodlouse. It is known by common names including "waterlouse", "aquatic sowbug" and "water hoglouse".