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Conservation-What Do You Call Them……Crayfish or Crawdads? By: Kevin Williams, Grundy County Conservation Director

July 6, 2018
Northern-Sun Print
I went fishing the other day. After looking over the choice of lures in my tacklebox, I chose one that resembled a crayfish. It was a good choice. And the reason that it was a good choice is that crayfish are an important food source for a number of fish species including the one I was after that day – Largemouth Bass. There are lots of common names for this animal. You might know it as a crawdad instead. Or a crawfish. Or maybe a mudbug. Or perhaps even a freshwater lobster. The cray or craw parts of the names because they do most of their movement by walking or “crawling” on the pond or stream bottom. And the mudbug name is easily seen, too. They are invertebrates with a hard outside skeleton – like insects. And in case you’re wondering, with a name like freshwater lobster, they not only look like lobsters but they taste like them, too. It just takes a lot more to make a meal. This jointed exoskeleton provides protection and allows movement, but limits growth. As a result, the crayfish regularly gets too big for its skeleton, sheds it, and grows a new larger one. This is called molting and occurs six to ten times during the first year of rapid growth, but less often during the second year. For a few days following each molt, crayfish have soft exoskeletons and are more vulnerable to predators. The head has two pairs of sensory antennae and a pair of eyes on movable stalks. They remind me of joysticks because they can rotate them independently. They have four pairs of walking legs. Crayfish also have one pair of large claw bearing legs. These strong pinchers are specialized for cutting, capturing food, attack, and defense. A pinch can hurt! A crayfish also has several pairs of specialized food handling "legs," which hold the food near the mouth, and five pairs of swimmerets which are under the abdomen. All of these "legs" can be regenerated if broken off. There are some 150 species in North America, over 540 species worldwide. Iowa has several species of crayfish including the prairie, virile, rusty, devil, and white river crayfish. Color and size varies with species, diet, and age. Most are red, some are green, brown, tan, or blue with black or orange markings in various combinations. Often juveniles will be a light tan color that turns to a deep red as an adult. The coloration depends in part on their diet, and can change with a change in diet. Adult size is 2" to 6" for most US species. Crayfish often conceal themselves under rocks or logs. They are most active at night, when they feed largely on snails, algae, insect larvae, worms, and tadpoles. Some eat vegetation (various water plants). Adults (one year old) become most active at dusk and continue heavy feeding activity until daybreak. Young crayfish are more likely to be the ones out during bright sunny days. General movement is always a slow walk, but if startled, crayfish use rapid flips of their tail to swim backwards and escape danger. Most crayfish live short lives, usually less than two years. Therefore, rapid, high-volume reproduction is important for the continuation of the species. The fertilized eggs are attached to the female' swimmerets on the underside of her jointed abdomen. There the 10 to 800 eggs change from dark to translucent as they develop. The egg-carrying female is said to be "in berry," because the egg mass looks something like a berry. Females are often seen "in berry" during May or June. The eggs hatch in 2 to 20 weeks, depending on water temperature. The newly-hatched crayfish stay attached to their mother until shortly after their second molt. As a kid, I remember wandering the banks of the creek that wandered through our farm and encountering my first crawdad chimney. These 4 to 6 inch towers of mud were the entrances to a crawdad burrow. The prairie crayfish is one of the species that digs such a burrow in low, poorly drained land that is covered with grasses or other prairie plants. Since so little prairie remains in the state today, it is found most often near ditches. The burrow may reach over six feet deep. The burrow is below the water table and water-filled. On moist nights or during periods of heavy rainfall, it may be found walking about on the soil’s surface. As I understand it, they do not necessarily return to the same burrow in the morning but lay claim to the first entrance they encounter. If it is already occupied, they get a pinch from the occupant and search elsewhere.

 
 

 

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