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18 scavenger and predator. 109 While they may be omnivores, they may act mainly as carnivores. 165 For instance, while they eat vegetation, they may be eating it to get at the invertebrates that live on the vegetation. The problem with food habits studies is that the usual procedure is to dissect out the stomach and examine the contents. However, crayfishes grind everything they eat into mush and the stomach contents often cannot be identified. 226 Furthermore, animal protein is more readily digested so it is not at all unexpected that most studies identify their food as "unidentified plant material". You can find a lot of crayfish food chain charts on the internet but I created my own chart shown here. It is an attempt to illustrate how crayfish may interact with the other organisms with which they live. The arrows show who eats what and the thickness of the arrow shows the strength of the interaction. In describing crayfish predation, some of the old literature has the most colorful language. In 1873, Abbott 1 observed that crayfish will "seize the minute young Cyprinoids [minnows], that pass up and down . . . peeping into the various little indentation in the banks. Such little fish when once fairly caught by the big. . . "hands" of a Cambarus, have no chance of escape, and are soon torn to pieces and devoured." He went on to note that ". . . darters. . . .will usually take shelter underneath a stone. . . When a crawfish happens to have taken up its abode under such a stone, it is seldom that the frightened darter escapes." Crayfish are also "skilled predators of tadpoles". 76 Crayfishes are also cannibals. Molting crayfishes, while still soft, can be killed and eaten by other crayfishes. 15 On a personal note, not long ago I had two Northern crayfish in an aquarium with an escape- proof cover. That is, on Friday there were two, on Monday there was one with no evidence that there had ever been a second in the tank. While all age classes may use plant material, adults do it more extensively. As an herbivore they function as shredders, collectors and grazers. 109 As shredders, they convert leaves, sticks, plants, etc. from coarse organic matter into fine organic matter. In turn, this fine organic matter may be used by smaller macroinvertebrates directly as food or indirectly as a substrate for algae and bacteria which can then be eaten. In a Michigan stream, crayfish (Orconectes propinquus) virtually eliminated a filamentous alga (Cladophora glomerata) which indirectly benefitted diatoms and grazing insects. 33 Crayfish, such as the Calico crayfish, can even act as filter feeders but it may be that juveniles must filter feed whereas adults may do so as needed. 16 MOLTING AND GROWTH Crayfishes are members of the order Arthropoda along with insects and arachnids. While "Arthropoda" means "jointed foot", their most important characteristic is that they all have an exoskeleton. The success of this group of organisms worldwide shows the advantages of this system. However, periodically, an exoskeleton must be shed and replaced to allow for growth. The technical term for