is the common name given to the insect order
Trichoptera, of which between 4,000 and 5,000
species are known throughout the temperate zones
of the world.
The most interesting feature of
the caddis flies is the life of the larvae, which
varies in the different families and genera. They
can be divided into two main types -- those which
build portable cases and are almost all
vegetarians, and those which live free and are at
least partly carnivorous.
The case-builders use many
materials in various ways to build their tubes.
Members of the genus Phryganea cut
pieces of leaves and stick them together with
silk, while those of the genus Limnophilus
use small stones and pieces of plant stems or
empty snail shells. If removed from their cases
and given beads or similar objects, some will use
the artificial material to make new cases. Stenophylax
and Heliopsyche use fine sand grains to
make their cases. Cases made of stones or sands
often have their weight reduced by a bubble of
air trapped inside.
All caddis fly cases are tubular and
open at one end; the larva pushes its head and
thorax out this end in order to feed and move
about. The other end is closed with a silken mesh
so that a current of water can flow through and
aerate the gills. All caddis-fly larvae have a
pair of hooked limbs at the back, used to hold
onto the case. So tightly can a caddis fly larva
grip with those limbs attempts to pull it out of
its case almost always result in injury to the
Most larvae with non-portable
cases live in silken tubes, in flowing water.
Larvae of the species Plectronemia make
a silk tunnel with the open end facing upstream
widely flared to form a trumpet-shaped net. Any
small animal or piece of plant material carried
into this "web" is seized and eaten by
the larva. Many other stream-dwelling caddis fly
larvae make nets of various shapes to gather
food. When they are damaged, or choked with
inedible material, the larvae clean and repair
Most tube-bearing caddis fly
larvae subsist primarily on the leaves and stems
of live plants. The large case-bearing larvae of Phryganea
catch and eat water insects as well as plant
food. Most of the tube-dwelling or free-living
larvae have a mixed diet.
The mouth parts of adult caddis
flies are vestigial, and they can take only
liquid food. In the wild they probably feed from
flowers with exposed nectaries.
Females lay their eggs in
spring and summer. Some drop them on the surface
as they are flying over, others crawl underwater
and stick them to stones or plants in a
Some of the larvae do not make
cases or tubes until they have moulted several
times, others make tiny cases as soon as they
When the larva is fully grown,
about a year after hatching, it pupates, inside
the case if it belongs to a case-bearing species,
otherwise in a silken coccoon. When the time
comes for the adult insect to emerge, the pupa
bites its way out of the case, being equipped for
the purpose with strong mandibles, and swims to
the surface of the water. There it splits open,
releasing the adult caddis fly, which can fly
almost immediately on emergence.
The life history of a caddis
fly lasts approximately one year, of which the
adult stage is but a very small fraction.
Dr. Maurice Burton and Robert Burton. Funk
& Wagnalls Wildlife Encyclopedia.
New York: Funk & Wagnalls, Inc., 1970.
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