What harm do crayfish cause?

Answer 1

Native species of crayfish that are are a normal part of the ecosystem are not harmful. But there are several invasive species, like the rusty crayfish, that can kill off native crayfish and other crustacians. The rusty crayfish has a thicker shell and less "meat" and therefore are are not a good part of the food chain depriving the ecosystem of the nutrients from the crustacians it replaces. Invasive species also tend to destroy large amounts of water plants that further degrade the food chain. Also there is an infection that occasionally occurs in crayfish that can spread to other animals but this is usually a normal part of the life cycle and not neccasarily harmful.

Answer 2

Crayfish can cause harm by disrupting local ecosystems when they are invasive species, outcompeting native species for resources. They can also burrow into riverbanks, causing erosion and destabilizing soil. In some cases, crayfish can also act as hosts for diseases that can impact other aquatic animals.