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15 (see photo at right). It is also a key characteristic used to identify the species. The most significant difference between the Astacidae and Cambaridae is with the variation in the form of adult males. In the Astacidae, the physical appearance of the first pleopod of a male, once it reaches maturity, retains its mature form for life. In the Cambaridae, the structure of the first pleopod alternates between mature (Form I) and immature (Form II) appearance. The Form II pleopod is soft and pale (photo below right). This changes to a mature Form I at the first molt after reaching sexual maturity. The Form I pleopod has a well- defined hardened projection (see photo above). The pleopod will then return to a soft Form II at the first molt after the end of the breeding season. This cycle repeats itself for as long as that male is alive. The presence of Form I and Form II males in the population in any particular season is variable and is related to their growth. Small males grow faster and molt more often so the spring and fall changes are more predictable. Large slow-growing males can retain their Form I pleopods well into the summer. A change in female form comparable to that seen in males has not been generally recognized but there is a way to differentiate between sexually mature and immature females. Mature females have swollen glair glands (photo below), dependent offspring, or the remains of egg cases attached to the pleopods. The change from mature to immature is also seasonal and only mature females will mate with mature males. 244 It has also been noted that mature females have a broader abdomen than immature females. 79 Sexual union may happen anytime mature males and females are together. Mating has been observed between June and October though the peak of activity was in late July and early August. 79 (I observed Calico crayfish mating on 9 July 2009 in the Niobrara River.) The process starts with a male approaching and grasping a female with one of his claws. Somewhat dexterously, he turns her over onto her back while holding onto her legs and claws with his claws. She curls her thorax up and he curls his down over hers in a face-to-face "spoon" position. After several minutes, he will rise up and pass one of his fifth legs to the opposite side, hooking his first pleopod which pushes it down. He then presses down forcing the point of the pleopod into the female's seminal receptacle. The hooks on the base of the male's third leg apparently are used to help lock them together at this time. 7, 8, 9 The transfer of sperm can now begin. The first pleopod has a groove from the base to the tip. The testis has an opening at the base of the male's fifth leg. A thin tube extends from this opening (the vas deferens) and connects to the basal end of the pleopod's groove. Sperm travels from the vas deferens, down the groove and into the seminal receptacle as "long, macaroni-like cords". The process can take several hours and the female barely moves during this time. Then the male rises up and releases the female. After completion, a waxy, white plug blocks the opening until egg laying which may not occur for several weeks or months. 7, 8, 9 When it comes time to lay her eggs, the female will look for a dark, protected area. At this time she is very excitable and assumes a defensive posture with any disturbance. The process begins with her propping herself up on her claws and tail in a tripod fashion. At this time she is using her fifth legs to clean the underside of her