Article for May - June 2012
For Wildlife Watchers: Crayfish
by Rob Simbeck
photograph by Phillip Jones
The life histories and distribution of many crayfish species in South Carolina remain a mystery, and new ones are still being discovered.
My first dose of the birds and the bees came from a crayfish. They were an endless source of fascination in an idyllic childhood world of trails and tree houses, slingshots and pocketknives. We slogged all day through creeks and ponds, jumped over fallen tree trunks, chased frogs and polliwogs, made spears and hatchets, imitated bird calls, and did a thousand other things that helped us learn about the world around us.
One of those was lifting rocks in the cold, clear water of the creek, watching crayfish scurry amid the sediment they'd kicked up. Catching them was labor intensive, but we had nothing but time. Mostly we'd just inspect them, watching the four pairs of legs and those great pincers wave in agitation.
One particular morning, we brought back a large one in a bucket and put it in an old tin washtub in the yard. The water was clear, and when we put our hands in, the crayfish raised those claws like twin buckets on a backhoe, holding us at bay. I studied it for the longest time and eventually noticed a tiny one beside it. How had I missed it? Then there was another, and another and another. Finally it dawned on my seven-year-old brain that this was a mother and her babies. Reproduction 101 was underway.
(species common to the piedmont)
(species common to the coastal plain)
Description: Like tiny lobsters, two to six inches in length in South Carolina. Range of colors, but most are reddish-brown.
Range and Habitat: Bodies of standing or flowing water. Some burrow into the ground. Forty different species are found in different areas of the state.
Reproduction: Male transfers sperm to female, who stores it until the eggs are fertilized, externally, and attached to swimmerets. Young remain attached to her through two molts.
Viewing Tips: Look under rocks or debris in creeks.
Depending on where you are, they may be called crayfish, crawfish (common in the South), crawdads or mudbugs. Freshwater crustaceans that look like tiny lobsters, to which they are related, they are famously served up in the Cajun cuisine of Louisiana, where they’re harvested to the tune of one hundred million pounds a year. There are more than six hundred species worldwide and three hundred in North America, and they can be found in most reasonably clean creeks, ponds, swamps and lakes — even sometimes in upland areas, where they burrow to find groundwater, leaving tell-tale mud chimneys.
The southeastern United States has the greatest number and variety of species in the world, and South Carolina has about forty, ranging in size from two to nearly six inches. All are members of the family Cambaridae, but they have adapted to any number of niches. Some species exist in just a few streams or a single cave system, while others are fairly widespread, although no single species is found in every South Carolina county. The variable crayfish (Cambarus latimanus) is probably most abundant in the piedmont, and the Eastern red swamp crayfish (Procambarus troglodytes) is most common in the coastal plain.
The life histories and distribution of many crayfish species in South Carolina remain a mystery, and new ones are still being discovered. Species-level identification can be difficult. Some have distinctive greenish-yellow to blue markings or colorings, but many are simply reddish-brown and can only be distinguished by microscopic examination of male individuals in certain phases of the breeding cycle. The red swamp crayfish (P. clarkii), brought in by the Natural Resources Conservation Service for aquaculture, for instance, is difficult to tell from P. troglodytes. Introduced species have been problematic in many places worldwide, sometimes spreading diseases and out-competing or even extirpating native species.
Crayfish have segmented bodies with a joined head and thorax packaged in a hard exoskeleton. Their legs have fracture plains along which they can be broken and, at the time of the next molt, regenerated. They have both short and long antennae that are highly sensitive to odors, compound eyes attached to stalks, and gills that must remain damp. Their muscular tails, as my friends and I well knew, are powerful enough to provide quick rearward escape.
Many live under rocks and debris on the bottoms of their aquatic homes, and they're omnivores, scavenging for living or dead plant and animal matter. They can tear up larger pieces of food with those outsized claws, or chelipeds, and propel the smaller pieces to their mouths with smaller specialized appendages.
Their reproductive organs are internal, with genital pores located in the male at the base of the last pair of legs and in the female at the third. Some specimens have the organs of both. The male has two pairs of modified swimmerets under the tail that transfer sperm to a structure on the female's belly. Females lay up to seven hundred eggs, depending on their size and species. Eggs are passed through the sperm, fertilized and attached under her tail. They hatch after a couple of weeks and the young stay under the tail through two molts, then gradually head out on their own, looking like tiny versions of the adults. At this point, they are preyed on by insects and other crayfish, and they will gradually serve as food for snakes, turtles, birds, mammals like otters and raccoons, and fish, including many game fish.
Humans, of course, savor them, and while Louisiana is known for its crawfish festivals — they're generally called crawfish when we're dining on them — South Carolina has been home to the Rosewood Crawfish Festival in Columbia since 2006.
Growth means regular molting, and as a crayfish prepares to molt, it absorbs calcium from its shell, depositing it in two white "stones" on its head. When a crayfish sheds its exoskeleton, it is vulnerable until its soft, flexible covering hardens, relying on the calcium from those stones. It may well eat its old shell after shedding it.
Their wide distribution and long-standing presence (their fossils go back 150 million years) have long been a source of interest, and the study of crayfish was one step leading to the theory of plate tectonics, which introduced the notion that massive plates on the earth’s surface move and that the continents were once connected.
Crayfish are not as sensitive to environmental pollutants as freshwater mussels, but are nevertheless bellwethers of our often-troubled relationship to nature, susceptible to the kinds of poisons that have long run into our waterways from fields and lawns. Habitat loss is a concern, as it is with so many creatures. The U.S. Fish and Wildlife Service lists four species as federally endangered. None of those are in South Carolina, although several here are species of special concern.
There are practical things we can do to help protect crayfish, some as simple as not dumping them from bait buckets into waters other than those where we got them. These are creatures we normally don't give much thought to, but anything capable of providing wonder and education for a child is surely worth preserving.
Rob Simbeck is an award-winning freelance writer living in Nashville, Tennessee.
Thanks to Arnie Eversole, with Clemson University's Department of Forestry and Natural Resources, William Poly, with the S.C. Department of Natural Resources, and Jennifer Price, a former DNR biologist who is now a postdoctoral researcher at the University of Virginia, for their invaluable assistance with this piece.
© 2012 South Carolina Wildlife Magazine, May - June 2012 - www.scwildlife.com