You Say Crayfish, I Say Crawfish
Aug 25, 2017 04:39PM
Every child who has encountered a crayfish in a Pennsylvania creek has admired its massive claws. Those claws can bring a stinging pinch to the hand if the crayfish is not held carefully by the body’s rigid outer shell, a structure scientists describe as an exoskeleton. Crayfish species all look pretty much the same, save for a few color differences. They are miniature lobsters, with the obvious difference being that crayfish live in fresh water while lobsters live in salt water, and that lobsters have two different types of claws, or chelae—one for slicing and the other for crushing. The next time you visit the grocery or seafood store, carefully examine the different claw types on the live lobsters.
Crayfish go by many other names, including crawfish, crawdad, mudbugs, and yabby. Pennsylvania currently hosts thirteen different crayfish species across the state, which is many more than the seven crayfish types Arnold E. Ortmann described in the 1906 publication The Crawfishes of the State of Pennsylvania.
In recent times, non-native crayfish have invaded Pennsylvania through bait-pail releases by fishermen and by others who do not know the harm that invaders can do to stream ecosystems. The most detrimental species, such as the rusty crayfish, are large, aggressive, and prolific breeders, displacing native species as they march across the state. Sadly, there is no way to control invasive crayfish except to avoid their release. The Pennsylvania Fish and Boat Commission has banned the transport of live crayfish by sportsmen. The new regulation states that you must kill the crayfish by removing the head if you wish to have them in your possession.
Native and non-native crayfish can be eaten, though they are much smaller than the southern red swamp crayfish favored by most restaurants and crayfish connoisseurs. Wildlife, including smallmouth bass, fallfish, great blue herons, muskrats, mink, and raccoons, eat them too. Two species that dine exclusively on crayfish are the giant eastern hellbender salamander and the queen snake, which curiously feeds solely on softshell crayfish. A softshell is one that has shed its rigid external shell while developing a newer, larger shell beneath. Once the older shell is shed, the new one is soft and remains so for a few days as it hardens. Molting of the exoskeleton is a lifetime process for crayfish, for as they grow they must regularly molt and replace the protective shell. How queen snakes find these soft treats is not known.
I have studied the crayfish of Pine Creek extensively and have found just two species. One is called the Appalachian brook crayfish and is historically native to the creek. It has small, beady, black eyes held close to the head and has a uniformly brownish-red exoskeleton. The other is called the Allegheny crayfish and is thought to be an invasive, though it does not seem to be in any way harmful to other aquatic life. It has oval, purplish eyes held away from the body on slender stalks and a body that has patches of green, blue-green, rust, and lavender, and red tips on the claws. The Allegheny crayfish is the dominant species from Jersey Shore upstream to Rexford. But from Rexford to Galeton, both species may be found. The Appalachian brook crayfish is the only species you will find in the headwater streams of Pine Creek; unfortunately for them, this is also where they are frequently the prey of colorful native brook trout.
Crayfish are omnivores, meaning they feed on anything. Grazing on algae-covered rocks, ingesting small aquatic insect larvae, munching on aquatic vegetation, or snacking on the carcass of a dead fish all meet the dietary needs of crayfish. Although it was long thought that they fed by grinding up food with their jaws or mandibles, recent studies have shown that sometimes an entire organism, such as a stone fly, is ingested.
One behavioral difference between the Allegheny and Appalachian brook cray sh species is that the Allegheny crayfish does not build burrows. Rather, it simply hides beneath stream rocks. The Appalachian brook crayfish builds burrows, either beneath cover rocks, or in sand and gravel sediments on shore where deep, excavated tunnels reach the water table below. A surface entrance to these tunnels is sometimes revealed by the presence of a crayfish “chimney.” Crayfish are gill breathers and have banks of moist gills beneath the exoskeleton. The protected gills allow them to survive out of water, though they prefer to be submerged.
The next time you encounter a crawfish, pick it up carefully with the thumb and forefinger grasping the rm shell behind the head so that pinching claws cannot reach you. Examine the underside of the tail where you will find a series of paired swimmerets—they look like skinny legs. Swimmerets are used by females to hold clusters of eggs until they hatch and discharge miniature crawfish, smaller than half the length of your pinky nail. A female holding eggs is said to be in “berry” because the egg clusters resemble the fruits of blackberries and raspberries. In males, the first pair of swimmerets are modified for reproduction and can be used to distinguish males from females. Breeding can occur at any time, but most commonly occurs in the fall.