Characteristics: (Minnesota Sea Grant) Rusty crayfish can generally be identified by their more robust claws, and by the dark, rusty spots on each side of their carapace. The spots are located on the carapace as though you picked up the crayfish with paint on your forefinger and thumb. The spots may not always be present or well developed on rusty crayfish from some waters.
Life cycle: (Minnesota Sea Grant) It is important to note that it is not necessary to have both a male and a female crayfish to begin a new infestation. One female carrying viable sperm could begin a new population if released into a suitable environment. Rusty crayfish readily mate in captivity so it is reasonable to expect that mature females, whether used as fishing bait or as science class study specimens, could produce offspring.
Eggs hatch in three to six weeks, depending on water temperature. Once hatched, young crayfish cling to the female's swimmerets for three to four molts (molting is when crayfish shed their old shell to allow growth). Young crayfish may stay with the female for several weeks. She offers them protection during this vulnerable life stage. Eventually, the young leave the female. They undergo eight to ten molts before they mature, which may occur during the first year, but more likely the following year. Rusty crayfish reach maturity at a total length of one and three-eighths inches and reach a maximum length of about four inches (not including claws). They averaged two and one-half inches in Wisconsin collections (Hobbs and Jass 1988).
Growth slows considerably after crayfish reach maturity. While mature males molt twice per year, females usually only molt once. Females molt after the release of their young, typically in June or early July. In the spring, males will molt into a sexually-inactive form (called Form II) and then molt back into the reproductively-competent form (Form I) in summer. Form I males are characterized by large claws, a hook on one pair of their legs (Figure 2), and hardened gonapods. The hook and the larger claws are used for grasping females during mating. Because males have an additional molt each year, they are usually larger than females of the same age. A typical rusty crayfish lives three to four years.
Methods of control: Commentary by Frank Splitt, Town Lakes Committee, Town of Plum Lake, September 11, 2006
Links to pdf documents
Indiana DNR
WI waterbodies with rusty crayfish
Links to other sites
Minnesota Sea Grant
Stop Aquatic Hitchhikers
Environmental Education for Kids
USGS
Crayfish recipes - The Vermilion Sportsman
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