INTRODUCTION. 
Caddis-flies, or Trichoptera, are winged insects with somewhat 
moth-like appearance, that are mostly nocturnal and usually do not 
wander far from the watersides. Only rarely do they become con- 
spicuous, and then on account of the great numbers in which they 
gather about lights, rather than on account of any striking indi- 
vidual habits or appearance. Occasionally they, together with 
mayflies and insects of a few other orders, congregate about elec- 
tric lights near large lakes and rivers in such numbers that they 
become a serious nuisance, and the bodies of their dead collect in 
piles that must be removed in wagon loads. Usually, however, 
one who is not making a special hunt for them sees no more than 
a few individuals that flutter around his light on warm summer 
nights preceding storms. 
Perhaps the larve, or caddis-worms—known also as “stick- 
worms’’—are more familiar to the average layman than the winged 
adults. Almost every child has seen a bundle of crossed sticks 
jerkily drawn about through the water by an insect with only 
head and legs projecting. Not all cases, however, are of the 
cross-stick type, and not all are so familiar to the layman. There 
are portable cases in almost endless variety of form, and made 
of almost every material to be found in the water, and there 
are many larve that make no portable cases, but live in silken tubes, 
awaiting animal prey or plancton to become entrapped in their 
catching nets. A few caddis-worms make no cases at all, but crawl 
free among the stones. 
Whether the caddis-worms construct portable cases, or silken 
tubes, or make no cases until almost time for pupation, they all 
secrete a glue, or silk, through openings in the lower lip, or labium. 
This silk is produced in large glands within the body cavity. 
These glands, like the silk-secreting glands of caterpillars, are 
modifications of the salivary glands, to meet the larve’s needs for 
silk. The silk is emitted as a liquid, but has the remarkable char- 
acter of hardening immediately after expulsion from the larve’s 
bodies and of adhering fast to submerged objects, though they be 
wet and saturated with water. The silk is not usually spun in fine 
strands, as is that of the Lepidoptera, but is more glue-like, form- 
ing a homogeneous sheet over the object cemented. 
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