Crayfish, also called crawfish (US), are closely related to the lobster, but unlike lobster, they live in fresh water environments. There are three species of crayfish in Finland. The native crayfish of Finland is European crayfish, also called noble crayfish (jokirapu). The second crayfish species was introduced from North America and is called signal crayfish (täplärapu). There is also a third crayfish species, but it only lives in the eastern parts of Finland and is called Narrow clawed crayfish (kapeasaksirapu). Crayfish are characterized by joined head and thorax, or midsection, and a segmented body, which is sandy yellow, green, or dark brown in color. Crayfish are usually about 7 - 15 cm long. 

The head has two pairs of sensory antennae and a pair of eyes on movable stalks. The appendages of the thorax include four pairs of walking legs, which, as well as walking, are to probe cracks and crevices between rocks looking for food. Crayfish also own one pair of claw bearing chelipeds, which it extends in front of its body while moving. These strong pinchers are specialized for cutting, capturing food, attack, and defense. A pinch can hurt! The crayfish also has several pairs of specialized food handling "legs" under the head, called maxillipeds to catch and slice pray, and five pairs of swimmerets, which are under the abdomen. All of these "legs" can regenerate if broken off. 

Crayfish have a hard outside skeleton (an exoskeleton). On head and midsection, this skeleton is joined together and is called carapace and it provides protection. On other places, this jointed exoskeleton provides protection and allows movement, but limits growth. As a result, the crayfish regularly gets too big for its skeleton, sheds it, and grows a new larger one. This is called molting and it occurs six to ten times during the first year of rapid growth, but less often during the second year. For a few days following each molt, crayfish have soft exoskeletons and are more vulnerable to predators.  

Crayfish are common in streams and lakes and they often conceal themselves under rocks or logs. They are most active at night, when they feed largely on snails, algae, insect larvae, worms, and tadpoles; some eat vegetation (various water plants). A dead fish and salmon eggs are also favorites of the crayfish. Studies show that adults (one year old) become most active at dusk and continue heavy feeding activity until daybreak. Young crayfish are more likely to be the ones outside during bright sunny days, while the older crayfish are more active on cloudy days and during the night. General movement is always a slow walk, but if startled, crayfish use rapid flips of their tail to swim backwards and escape danger. 


Crayfish eggs