Signal Crayfish: a two-minute wildlife lesson

Crabs and Shells · day 3 of 7

Five facts

1. Its name comes from a pale patch on each claw joint, which looks like the white flags railway signalmen once waved at trains.
2. It is a night owl. In lab tests with 12 hours of light and 12 of dark, 72% of its activity took place in the dark.
3. It is a tough fighter. Against spiny-cheek crayfish, it kept winning and was happy to keep up intense fights.
4. Mothers carry their eggs all winter long. The babies hatch when the water warms, usually in March or April.
5. Brought over from North America, it is now the most widespread foreign crayfish in Europe, found in 27 countries.

The quiz

1. Where does the signal crayfish get its name?

• It flashes light at night
• A pale claw patch like a signal flag (correct)
• It taps messages with its tail
• It lives beside railway lines

The light patch on its claw joint looks like a signalman's white flag.

2. In lab tests, how much of its activity happened in the dark?

• 72% (correct)
• None of it
• About 10%
• About 30%

On average, 72% of its activity took place during dark hours.

3. What usually happened when signal crayfish met spiny-cheek crayfish?

• The signal crayfish ran away
• They ignored each other
• The signal crayfish came out on top (correct)
• They shared their food

The signal crayfish kept winning and kept fights going.

4. When do the eggs usually hatch?

• June or July
• September or October
• December
• March or April (correct)

Mothers carry the eggs through winter, and they hatch around March or April.

5. In how many European countries is the signal crayfish found?

• 2
• 27 (correct)
• 8
• 50

It is the most widespread foreign crayfish in Europe, living in 27 countries.

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