Essays
Moseying: Exploring the Natural World
Crayfish or Crawdads live in Midland County
September 19, 2010
Years ago I released crawdads into the Sibley Nature Center pond among the quickly reproducing cattails and sedges. For a year and a half I saw no sign of the crustaceans. Finally in late summer I noticed parts of shells (where they'd moulted) and one set of more complete remains, left by a Great Blue Heron evidently too sated to complete his meal. I also noted one mud chimney on the banks. (A mud chimney is built up at the mouth of the animal’s burrow.)
Later that fall I at long last spotted a live one in the shallows, drifting on its side, listlessly waving its feet. I thought it sick. The next spring I noticed two very small crawdads that spent a day and a half to shed their exoskeletons, drifting aimlessly. They finally righted themselves and scooted about the pool, shooting backwards with vigorous flips of their tails. A few days later they disappeared, but the next year there were from four to eighteen at a time in the shallows, feeding, scooting backwards if disturbed, and casually interacting when bumping into each other. On a night hike one evening, I saw several clambering about over the submerged grasses that were six-inch to seven-inch monster crawdads, far bigger than any we had seen. When we drained the Sibley pond this year, we did not find one. Predators had eliminated the small population.
Looking through the Sibley Center library that first year, I found only a few paragraphs of information. In the UTPB library a friend found T.H. Huxley's The Crayfish, published in 1880. Most of the book is a complete physiology, with even the smallest part described and explained in teleological terms of function - in other words, far more than I care to know about crawdads. Now there are websites devoted to crayfish.
A few of the unique features of crawdads are the differences between sexes, eating habits, and the process of shedding their exoskeleton. Female crawdads have broader tails than males (they carry eggs and young there). After mating, females carry, the eggs for two months, then over the next two months the eggs hatch in waves. For a week the young continue to hang to the swimmerets of the female ---(tiny claws along the tail), then detach themselves, but return at any sign of danger for another few days. Crawdads eat anything - insect larvae, snails, tadpoles, frogs, voles and pocket mice. Plants are on the list too, and they are not above eating each other.
Instead of having an internal bony skeleton, crawdads are enclosed in a two layer envelope - the integument. The outer layer of the integument is composed mostly of lime salts and chitin - the cuticle. The cuticle hardens and forms a protective plate over each of the 20 or more pairs of appendages, but remains pliable to form the hinge between the adjacent plates when the exoskeleton is replaced.
Replacement of the exoskeleton is called ecdysis or exuviation. It may take from a few minutes to many hours and is exhausting, dangerous and sometimes damaging. It may cause the animal to die or to lose an appendage or two. The appendages usually grow back. In replacing the exoskeleton, the animal performs a series of maneuvers. Before the process commences the crawdad rubs its limbs together, throws itself on its back, bends and stretches its tail, vibrates its antennae. This loosens the various parts in their sheathes. Then, like a man sucking in his belly to fasten a too-small coat, the crawdad slowly retracts the limbs into the body interior. Next the connection between the tail and carapace breaks so that the animal is forced out as the carapace is forced forward. The head is next withdrawn, then the legs. The last to emerge from the hard outer "shell" is the stomach, which is popped out when the animal suddenly springs forward. This leaves the animal out of its old exoskeleton and protected only by a soft integument. It takes awhile for the muscles to get back into normal position. The animal grows for about three days before the cuticle layer hardens to enclose it in a new exoskeleton.
Crawdads are found in Midland Draw just south of the railroad (on private property), along Scharbauer Draw in town, and at the I-20 preserve in southwest Midland. I am now allergic to them, but I used to love eating mudbugs! On September 20th, at 6.30 p.m, come to the Siobley Nature Center to the Midland Naturalist's annual meeting, and listen to Elaine Magruder talk about the I-20 preserve.
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