THE ANIMAL FILES

Noble crayfish

Astacus astacus

A night forager with a sheltered daytime address.

The noble crayfish lives in freshwater habitats and uses shelter as well as food. It eats both animals and plants, while fish and mammals can eat the crayfish itself. Its role in a stream changes with what it is doing: feeding, hiding or carrying the next generation.[1]

Follow the evidence ↓
Noble crayfish
Image: H. Zell · Commons · CC BY-SA 3.0
Water
Freshwater streams, rivers and lakes[1]
Activity
Mainly nocturnal[1]
Egg care
Eggs attached beneath the female[1]

Shelter changes what you see

Noble crayfish are nocturnal, resting in burrows by day and favouring abundant shelter. A daytime survey of open water can consequently miss individuals that are present.[1]

A mixed menu

Worms, aquatic insects, molluscs and plants all appear in its food list. At the same time, eels, perch, pike, otters and other predators take crayfish. The animal therefore connects several parts of a freshwater food web. Calling it a predator alone would hide plant consumption and its own role as prey.[1]

Eggs travel with their mother

After fertilisation, eggs remain attached to the female’s swimming appendages beneath the abdomen until hatching. The young later disperse. The mother therefore carries the developing eggs rather than releasing them immediately into open water.[1]

A COMMON MIX-UP

Is every meal captured animal prey?

No. Plants are also part of the recorded diet. An animal with large claws can still use more than one food source.[1]

TRY A LITTLE REASONING

Why would few visible crayfish at midday be weak evidence of absence?

Reveal the explanation

They are mainly active at night and shelter during the day. Visibility depends on activity time and shelter, not just how many animals live there.[1]

Sources & editorial notes

Adapted and translated from the cited Wikipedia revisions, with source-linked reasoning. Image credit and licence are listed separately above.

Adapted and translated from Wikipedia contributors; exact revisions are linked below. CC BY-SA 4.0

  1. Wikipedia contributors — Astacus astacus (adapted and translated; exact revision)
  2. NCBI Taxonomy — Astacus astacus (identity and game lineage)

Last fact check:

One discovery leads to another

European lobsterTwo claws, two different kinds of work.Homarus gammarus ↗Norway lobsterFor this lobster, the right mud is an address.Nephrops norvegicus ↗European green crabA green crab can be red—and still be the same species.Carcinus maenas ↗