Caddisflies- Trichoptera

Just after sunset hordes of winged insects are often seen rising from the surface of canals, rivers, mountain streams, rice pad- dies, and ponds, beginning another night in their nocturnal existence. Among the waves of night flyers may be mayflies, mosquitoes, beetles, and large numbers of moth like in- sects with long, hair-covered wings. These last insects are known as caddisflies. They are members of the order Trichoptera.

 

The Trichoptera are dull-colored insects usually found near water. The antennae of the Trichoptera are long and thin. Their compound eyes are seldom prominent; how- ever, the males of some species have large, protruding eyes. The adults primarily feed on liquid food; their mouthparts, with the exception of the palpi, are rudimentary.

 

They have soft bodies that, like their wings, are covered with long hairs. Both pairs of wings are membranous and are held tent like over the body when the insect is at rest. The front wings are usually longer and somewhat narrower than the back pair. In a few species the wings have scales. The caddisflies with scaled wings are frequently mistaken for butterflies.

 

 

The Trichoptera undergo complete metamorphosis. The female lays her eggs in the water or on objects near the water, usually depositing several hundred at a time. The eggs are encased in a gelatinous mass that swells as it absorbs water. The various species of Trichoptera can be identified by the shape of the gelatinous mass and the arrangement of the eggs within it.  

Known as caddisworms, trichopteran larvae almost always develop under water, breathing by means of blood gills, tracheal gills, or a combination of both. They resemble caterpillars. Each has a distinct head, chewing mouthparts, and a pair of hooked appendages at the end of the abdomen.  

In some species, the larva constructs a portable case to protect its abdomen. These cases, which the larvae drag behind them throughout their development, vary considerably. They may be tubular, spiral, or even prism-shaped. Some cases are constructed of pure silk, spun from modified salivary glands through an opening in the labium. More often they are constructed of sand, pebbles, shells, twigs, and leaves, all bound

together with silk. When the case-building larvae are fully developed, they attach their cases to objects in the water and then pupate in them. The new adults cut their way out of the cases with their sharp mandibles.

Other trichopteran larvae, usually found in swift water or along the banks of lakes, construct elaborate silk nets in which they trap their prey. The nets are anchored to submerged plants or rocks with the open end facing against the current. The builder waits nearby for victims to fall into its trap. The net-building larvae pupate in tiny cells.

Some trichopteran larvae build neither cases nor nets. These larvae, like the netbuilders, are predaceous, feeding on small aquatic animals. The case-building larvae are primarily plant feeders.

The Trichoptera may spend as long as a year as larvae. The adults, however, usually live less than a month.

The Trichoptera is a relatively small order, with only about 3,000 known species. These insects occur mainly in the temperate regions of the northern hemisphere.

Trichoptera have little economic importance, but they are usually considered beneficial to man since they are an important part of the diet of many fish.

Some experts are able to identify the various groups of the net-building Trichoptera by the shape of the nets they spin. The larvae of the family Psychomyiidae, for example, construct trumpet-shaped nets, while the Hydropsychidae spin cup-shaped nets.

Rhyacophilidae. Trichoptera of the family Rhyacophilidae, the primitive caddis flies, have mottled wings and short antennae. In some species of the subfamily Glossomatinae the larvae are case-makers. In species of the subfamily Rhyacophilinae the larvae are free-living. The members of this family are usually found near swift streams.

Philopotamidae. The larvae of the family Philopotamidae, the finger-net caddisflies, also live in swift streams. They construct fingershaped nets which they attach to stones; they pupate in silk-lined cases constructed of pebbles.

Limnephilidae. The larvae of the Limnephilidae, or northern caddisflies, are case-builders and are found in ponds, lakes, and slowmoving streams. This large family displays several unusual characteristics. At intervals during their development the larvae of the Limnephilidae shed their cases and build new ones. The cases of the older larvae differ considerably from those made by young larvae.

Philocasia demita, a species found in Oregon, is notable in that its larvae are found on the ground, usually in piles of damp leaves.

Leptoceridae are distinguished by extremely long antennae, often stretching nearly twice the length of the insect's body. Called longhorned caddisflies, these Trichoptera are usually light in color. Leptocerid larvae are case-makers, and, depending on the species, construct cases that are torpedo, or cornucopia-shaped.

Helicopsychidae are called snail-case caddis flies. The larvae of this family construct cases resembling snail shells.

Goeridae. The larvae of this family build their particular cases out of the very tiniest of pebbles, which they painstakingly collect in the vicinity. To these they attach much larger pebbles, adding greater weight to the sides of the cases and serving to anchor them so that they are not swept away in swift waters or destroyed by thunder showers.


 

INDEX : Insects   May 27, 2014 09:07:22 AM