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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. [108]-123 PDF (5.1 MB)


Page 109


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
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