The Carlisle Mosquito Online

Friday, August 28, 2009

 

Crayfish

 

Everyone I have spoken to recently about crayfish says the same thing – “I used to find them all the time when I was a kid.” These are people who no longer spend their free time in streams turning over rocks. But after a very wet month in July, it was possible to find a crayfish with a lot less trouble. Kate Reid spotted one on August 1 crossing the road on Carleton Road! It was about four to five inches long not counting antennae and a distinctly reddish-brown color. When Kate approached it, it demonstrated the typical crayfish defensive behavior (when out of the water) of raising the front end of its body and waving its pincers ready to attack. Kate offered it a stick which it obligingly grabbed so she could then carry it safely off the road. Earlier in the year, on April 24, Bonnie Miskolczy found a crayfish in the pond on their property on Cross Street. It was dead. It was a similar size to Kate’s and the color was much darker – which may not have been the case when it was alive. Typical crayfish lifespan is two years.

Name: The crayfish name is a corruption of the French word écrevisse which you may see in some English language recipe books. In the southern U.S., crayfish are commonly called crawfish, crawdads or mudbugs. From the information I could find on the web, the primary interest in them in the southern states is a culinary one. Crayfish aquaculture is big in Louisiana with annual production of many millions of pounds.

Classification: There are around 500 species of crayfish worldwide and 300 species in North America. The website for Global Crayfish Resources lists 37 species for Louisiana, 68 species for Georgia and only 5 for Massachusetts. A closer look at the Carleton Road specimen would be needed to determine its species. Crayfish are crustaceans all of which have two pairs of antennae. Crayfish, along with crabs, lobsters and shrimps are in the order Decapoda which is a reference to the ten “legs” attached to the thorax. The first pair is larger than the others and bears the pincers or claws. The remaining four pairs, in the crayfish, are adapted for crawling. Crayfish, and other crustaceans, are well-endowed with appendages. In addition to the antennae they have three pairs of feeding appendages attached to the head, and they have five pairs of little leg-like attachments called pleopods or swimmerets on the abdomen. Even the eyes are on the ends of stubby appendages.

Why did the crayfish cross the road? Crayfish are omnivores and are known to leave their pool or stream to forage along the shore. Since the gills are protected by the carapace they can stay moist for some time when the crayfish is on land. And they can tolerate fairly low oxygen levels, so are able to venture from the water for short periods. When Kate spotted her crayfish, the road was still wet from the recent rain.

Food chain: Crayfish are preyed upon by snakes, otters, mink, racoon, birds and fish – not to mention humans. The reason crayfish can be found by moving rocks in streams is that they use the rocks as protective cover from their predators. They are most active at night when they forage for other aquatic invertebrates, tadpoles, fish, fish eggs and plants.

Word for the day: The study of crayfish is called astacology.

Sources: Invertebrate Zoology, Robert D. Barnes; Living Invertebrates, Pearse and Buchsbaum; Carnegie Mellon Global Crayfish Resources at iz.carnegiemnh.org; Manitoba’s online nature magazine at naturenorth.com. ∆


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