Skinner, Ernest B. (ed.) / Transactions of the Wisconsin Academy of Sciences, Arts and Letters
volume XV, Part I (1904)
Vorhies, Charles T.
Habits and anatomy of the larva of the caddis fly, Platyphylax designatus, Walker, pp. -123 PDF (5.1 MB)
109 vorhies-Larva of Platyph'ylax Designatus. ously dragged away to a new retreat by a visible brown head and six legs. Hundreds of these larvae may be seen in a few minutes time in this one group of springs. The case is very beautifully constructed of sand grains, and is in the form of a slightly curved tube, (Fig. 21.) open at both ends, though the posterior, narrower end, usually has the mar- gin turned in so as to partially close the orifice. (Fig. 22.) The concavity of the case is ventral and a slight projection or hood extends forward from the dorsal portion of the anterior mar- gin. The eggs of this caddis-fly are deposited in large numbers in April. They are attached to the lower surfaces of loose stones, mostly at the edge of the water, in very monist situations. The larvae hatch in a short time, probably in less than two weeks, though the exact time has not yet been determined. They are about 11,4 mm. in length when first hatched, and their heads are larger and legs longer relatively than the same parts of older larvae. The interesting fact was noticed that these newly hatched larvae are positively heliotropic to a marked degree when on a dry surface, but at once become negatively helio- tropic when placed in a dish of water. The necessity of getting out from beneath the stones where the eggs are placed in order to find water, and of getting beneath stones for protection while building a case, after reaching it, offers an explanation of this peculiarity. The young larvae at once begin building cases when placed in a dish of w-ater with sand in it, and are capable of fashioning a fairly good one in four or five hours. They probably do not feed until safely housed in a case. Small larvae a few millimeters in length are plentiful in the late summer and early fall. From November to January more and more larger larvae are found and small individuals become few in number. About the middle of February the majority of the cases are found to have larger irregular stones attached to the anterior ends, evidence of the approach of pupation, while some are found fastened to the lower surfaces of the large rocks by a mass of silk at the anterior end. Many of the latter are also closed at the posterior end with larger stones of the same kind as those already mentioned. If the closed cases be broken open I I ---
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