Native Animal Profile: Crayfish

A biologist holds up a crayfish found in the Patapsco River. Maryland Department of Natural Resources photo

Most of us who have played in shallow water or let our children play in Maryland streams and pond, vividly recall an encounter with a crayfish. It’s usually hiding under a rock, hurriedly scampering along a sandy stream bottom, shooting quickly backwards away from disturbance, or angrily shaking small claws at us as we pluck it out of the water. This creek critter is uniquely charismatic and still quite common despite the increase in threats to its survival. Whether you call it crayfish, crawfish, mudbug, crawdad, freshwater lobster, or another of many common nicknames, this humble crustacean is often seen but not often fully appreciated.  

*Did you know? The scientific study of crayfish is called Astacology, from the Greek word astakós (ἀστακός) which means crayfish or lobster, and Astacus – the Latin genus name for European crayfish.*

Maryland is the proud home to a total of 14 species of crayfish, nine native species in four genera, and five introduced or invasive species. We’ve got just a small piece of the species distribution pie, with more than 640 species total found globally. The southeastern United States boasts a hotspot of global diversity, with more than 370 species dwelling in our ideal freshwater ecosystems. Crayfish and lobsters don’t just look alike – they are closely related even though crayfish are found in freshwater and lobsters prefer saltwater. A classroom dissection or perusal of a field guide or key will demonstrate the many nuances of their complex anatomy. They have ten legs, two of which are claws (called chelipeds, and often lost in battle), strong abdomens for speedy backwards swimming, and feathery gills for breathing underwater. Sometimes you’ll encounter one that’s soft and squishy, having just molted its exoskeleton to allow for growth, get ready for mating, or in response to environmental stimuli. The largest crayfish in the world are quite impressive, growing over two feet long, but these hefty specimens do not dwell in our part of the world; our largest species max out at closer to five inches.

As a keystone species, crayfish hold an important place in the center of freshwater ecosystems. Like beavers, crayfish are widely considered “ecosystem engineers.” They physically modify their environments by foraging, substrate restructuring, and burrowing; three of our Maryland species build characteristic “chimneys” when they burrow in the mud. These movements and behaviors influence sediment, water, and nutrient flow, creating microhabitats and increasing overall biodiversity. Crayfish serve as omnivorous scavengers and predators, eating just about anything they can grab, other animals’ leftovers, and sometimes even each other! As prey, they feed many hundreds of other species, composing a large part of the diets of countless fish, reptiles, birds and even some mammals. Humans like to eat crayfish too, and we can catch them via various methods here in Maryland with a fishing license. The US crayfish industry is valued at more than $200 million annually.

Despite the appearance of abundance in our local streams, crayfish are in fact one of the most vulnerable groups, with a high percentage of overall species listed as imperiled or rare. The Endangered Species Act came about in 1973, but it wasn’t until the late 1980s that any crayfish were recognized and listed for Federal protection. Right under our noses in streams all over Maryland, many native crayfish are struggling to survive under heavy pressure from invasive species. Unlike most other imperiled animals, local population declines are influenced more by non-native crayfish  introductions than habitat loss. These animals have been moved around extensively, introduced all over the world via released bait and aquarium pets, as well as some intentional stocking for food or biocontrol purposes. Like other invasive species, they compete with and often introduce disease or hybridize with the native species, causing a severe and rapid decline in biodiversity. Contrary to popular belief, more prey items for fish doesn’t necessarily mean more fish for fishermen. Studies have shown that invasive crayfish can hurt recreational fisheries and create negative economic impacts.

Though we may have been the cause of the crayfish’s population decline, we can also be a major contributor to their recovery! Here’s how:

• NEVER release bait animals (alive or dead) or any pet into the wild, or move wild animals from place to place.

• Create a great crayfish habitat in your backyard! If you own property with a stream or pond (or even a drainage ditch), plant your buffer areas with native plants. Even if you don’t have water in your yard, every Marylander lives within 15 minutes of a stream. Planting natives will increase water quality and keep water temperatures cooler in our changing climate.
• Give crayfish some love. Teach your friends what you’ve learned! If you’re a teacher, help students understand aquatic invasive species. 
• Don’t have them in your yard, but want crayfish on your wall?  Download our free PDF or get a poster! https://dnr.maryland.gov/wildlife/PublishingImages/crayfish.jpg 
• Do you like to eat crayfish? Get a fishing license, learn to identify them, and go catch  some invasive crayfish for dinner tonight (consider a side of garlic mustard pesto pasta and wineberries)! 

Fact sheets on invasive crayfish:

https://dnr.maryland.gov/invasives/documents/virilecrayfish10.pdf

https://dnr.maryland.gov/invasives/documents/rustycrayfish10.pdf

https://dnr.maryland.gov/invasives/documents/redswampcrawfish.pdf

https://dnr.maryland.gov/invasives/documents/southernwhiterivercrawfishfactsheet.pdf