NATURE NOTE - Number 92 May 14, 2024
Introduction:
As summer approaches, the opportunity for scouts to see an animal that is out there, but not often found or seen is…
Our current topic: Crayfish, crawdads or crawfish.
They go by different names, with certain names favored in different parts of the country. Like lobsters, they are crustaceans in the Phylum Arthropoda (along with insects, spiders, centipedes, etc.). There are over 250 species of crayfish in North America, and about 30 species in Virginia; most native, but some introduced. Most are fresh water, breathing through gills located above the legs. They are a critical part of food chain providing food to a wide range of animals from raccoons, large birds, reptiles, amphibians and larger fish while acting as a scavenger of small stream bottoms.
Their characteristics include a joined head and thorax with a pointy snout and large eyes, large pincers and other legs used for swimming. Commonly, their length is in the 2”-4” range. Color varies from brown, green, white, blue, red, and black to blend in to stream bottoms. A thin but tough exoskeleton is shed several times in early life as the body expands beyond the old shell. During this time, the animal is very vulnerable and avoids venturing outside its burrow. Females lay eggs in the spring and the eggs remain attached to the mother’s body. When they hatch, they are very small versions of an adult.
These critters can be found in ponds, but most live in more oxygen-rich flowing streams. The Common Crayfish or Brook Crayfish (Cambarus bartonnii) is found in wide range of streams including very small headwaters of many rivers draining our council area. Mostly nocturnal, they hide under rocks during the day, feeding on snails, worms, tadpoles, and insect larvae. Some crayfish are burrowing crayfish that are seldom seen above ground. They dig deep holes in stream banks and moist sites, including yards where they leave their tell-tail mud “chimney”. Burrowing in mud or very moist lawns, they need saturated soil.
Identification by the casual observer is almost impossible due to the lack of field guides covering crayfish. In some cases, exact ranges with Virginia have not been firmly established. Some species are quite endemic to specific rivers and feeder streams to that river. This means they may not be found anywhere outside of that particular river system. Since our council includes rivers flowing east into the Atlantic, and others flowing north and south into the Gulf of Mexico, some species we might encounter are totally separated. Some species will overlap into different river systems. Some of the more common crayfish in Virginia include Brook crayfish, the Atlantic Slope crayfish (found, appropriately, in the Roanoke, Yadkin and James rivers), and the Spinycheek crayfish (found in the James, Potomac and York rivers). Most of the non-native species in Virginia have been introduced by humans using various species as fish bait. As an example, the Rusty Crayfish, native to Ohio River Valley, is a non-native found in Virginia streams. It is large and aggressive, causing decline in native species. In Virginia, it’s illegal to sell crayfish for bait, and you should avoid releasing any crawdad into a stream other than the one it was taken from. One species from Louisiana, the Red Swamp crayfish, has been released in eastern Virginia so often it now is common in warmer waters of the Coastal Plain and the Piedmont region. The Ozark crayfish, a non-native species, is also common in the James and Roanoke rivers.
One species, the Big Sandy crayfish, has been on the endangered species list since 2016 in southwestern Virginia, Kentucky and West Virginia. It is particularly sensitive to high sedimentation in streams often caused by improper logging and mining activities. Some species are quite sensitive to pollution and therefore are indicators of water quality. The state Department of Wildlife Resources is cooperating with other agencies and universities to learn more about the impact of water quality on crayfish distribution. One major successful effort was to produce the first juvenile Big Sandy crayfish in captivity in 2022.
Almost all freshwater crayfish are edible, and crayfish are a big food source worldwide. The U.S. produces nearly 80,000 tons per year. Most are trapped in the wild and then reared in farms in the Gulf States to be sold as food or bait.
Opportunities:
I’m not sure what special opportunities there are for “crayfish watching” by scouts, but a couple of teaching points might be made. The first is the lack of detailed knowledge about species identification, habitat, range, pollution threats, etc. This shows that we don’t know everything about nature. There is lots of room to explore. Who is going to do that? Another point is diversity of species and how some species are so closely tied to a specific water system. They can’t walk or fly, so their opportunity to move to a new habitat is very restricted. This means when pollution or another threat reduces the population in one river system, it may be the ONLY population and endangers the existence of the entire species. And, it appears many non-native species exist, and compete, with native species because of human action. All of these points seem to be well illustrated by crayfish.
As always, do what you can to expose scouts to nature. Turn over that rock in that stream and see what’s there.
Thanks for reading NATURE NOTES. Write me at:
Bob Garst
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One of the authorities on this animal group is a biology professor and researcher at Washington and Lee University in Lexington, Dr. Paul Cabe. His article in the fall 2023 Virginia Wildlife was a source of much information in this NATURE NOTE.
