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Little Lobsters? Crayfish Are a Close Relative

Of course we don’t have lobsters here in landlocked Will County, but don’t be surprised if you see what looks like a miniature version in your local pond. These little creatures are crayfish, and lobsters and crayfish are closely related.

(Photo courtesy of Yu Cheng)

Like lobsters and other common sea creatures such as crabs and shrimp, crayfish are crustaceans. Most of the crustaceans we are familiar with are aquatic. What all crustaceans have in common is that they have a hard exoskeleton, paired and jointed appendages and three body regions: a head, a thorax and an abdomen.

Crayfish belong to the order of Decapoda, a term that translates to ten-footed. Their 10 feet include four pairs of walking legs plus their most dominant physical characteristic, a large set of claws, which they use to hunt for food and defend themselves from predators.

Their legs and claws have a superpower. If a crayfish is caught, it can amputate its own legs or claws to escape thanks to a muscle reflex. These appendages aren't lost forever. The amputated legs and claws will grow back over time. This is why it's not unusual to see crayfish in the wild with legs and claws of different sizes.


Words to know

Amputate: To cut off a limb.

Appendage: A projecting body part on an invertebrate or other organism.

Exoskeleton: A hard external covering of the body for some animals.

Landlocked: Entirely surrounded by land.


Like other crustaceans and arthropods, crayfish molt as they grow. Because their exoskeletons are hard and inflexible, they eventually outgrow them and replace them with larger ones. When they are young and growing quickly, they molt frequently, sometimes even daily. As they get older and bigger, the molting becomes less frequent.

In the days after a molt, their skin is soft, which makes them more vulnerable to predators. They are able to grow their new, larger exoskeletons by eating the old shells, which contain calcium.

Crayfish will eat just about anything they come across, but they mainly eat plants and dead animals. They will also use their claws, also called chelae, to catch fish, insects and other invertebrates. Crayfish play an important role in the food chain because they are a food source for a variety of animals, from mammals and birds to reptiles and amphibians.

(Photo via Shutterstock)

Crayfish mostly live alone, coming together only to mate. They usually mate in the fall, and the female will lay eggs the following spring. The females then attach the eggs, sometimes numbering in the hundreds, to their abdomens using a glue-like substance. After several weeks, the eggs hatch, but the young crayfish remain attached to their mother's abdomen until after they molt twice. After that, they will begin venturing out on their own, returning if they are threatened.

Crayfish live in freshwater habitats almost everywhere, with the exception of Antarctica and India. There are about 600 species in all. Some of the areas with the most diversity of crayfish are the southeastern United States and Australia. Illinois is home to several kinds of crayfish. Among the most common are the devil crayfish, digger crayfish, northern clearwater crayfish, prairie crayfish, rusty crayfish, virile crayfish and white river crayfish. Most local species are native, but the rusty crayfish is an invasive species that is native to the southern United States.

Rusty crayfish are aggressive and can take over habitat areas from native crayfish species. In some places, they have eliminated native species from their original habitats entirely. They are found mainly in the northern part of the state, and they have been here since at least 1973. It is thought that they were accidentally introduced by fishers who used them as bait and released unused crayfish when they were done fishing.

What we call a crayfish here in Illinois goes by many other names both in the United States and beyond. In the South, crawfish is the more common name, and in some parts of the United States they are most commonly called crawdads. In some places, mudbug is the preferred term, and in Australia they are known as yabbies.

No matter what you call them, they are considered a keystone species, which means their presence is vital to the health of the ecosystem. However, of the more than 600 crayfish species in the world, including about 400 in the United States, 32% are threatened with extinction.

Reasons for their population decline vary across the world. Here in the United States, major factors include the building of dams, development of urban areas, pollution and habitat loss. In Australia, climate change is a large factor, putting 65% of species at major risk, along with competition from invasive species, agricultural development and overharvesting. In the United States, 5% of species are at increased risk because of climate change.


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