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Crawfish

July 23, 2017
Kevin Williams - Grundy County Conservation Director , Reinbeck Courier

My grandson, Tate, went to Florida last week for a family vacation. He went with the request to pick out a nice shell for Grandpa.

We stopped by his house after they returned and he was standing at the open door when we pulled into the drive holding two shells. One was for Grandma and one for me.

He told us all about his trip. The plane ride. The place where they stayed. The taste of saltwater. And the animal life they saw manatee, pelican, stingray, dolphin, etc. And then he shared looks at the bag of shells that had traveled home with them.

After Florida stories, he told me about the trip they took to the lake after returning home. "Did you catch any fish?" I asked. "No, but I caught a crawfish," he quickly answered.

Now, this little guy reads his Ranger Rick magazine cover to cover each time one arrives in the mail. He proceeded to tell me all about crayfish. I thought I would share a few things he told me (and a few more he didn't).

There are lots of common names for this animal. You might know it as a crawdad instead. 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, they not only look like lobsters but they taste like them, too. It just takes a lot more to make a meal.

Crayfish regularly gets too big for their 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. Adult size is 2" to 6" for most US species.

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.

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. 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. Kind of a crawfish musical chairs!

 
 

 

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