Trichoptera

Introduction

Caddisflies. A medium sized order (large for an aquatic order) of about 7,000 species worldwide, but with a moderate rate of new species descriptions. There are about 1600 species in North America through Mexico. Related to the Lepidoptera. The larvae make extensive use of silk. Endopterygota- holometabolous.

Recognition

Larvae- no wingpads, thoracic legs well developed, no abdominal prolegs, antennae one segmented and inconspicuous, last abdominal segment with anal hooks, often in cases or silk retreats. Pupae- exarate, antennae with more than 11 segments, mandibles stout and usually crossed, underwater in cases. Adults- two pairs of membranous, hairy wings held roof-like over the abdomen, antennae conspicuous, mouthparts without a coiled sucking tube.

Life Cycle

Eggs may diapause for some time or hatch into first instar larvae. The first instar may remain in the egg's gelatinous mass for some time. Most species have five larval instars. Most species are univoltine; a few are multivoltine in warm waters, nonseasonal in springs, or semivoltine in cold waters. The last instar is usually of the longest duration and does most of the feeding. There may be larval diapause. Pupation occurs underwater in the case or retreat of the last larval instar or in a specially built structure. The pupa uses its large mandibles to cut out of the pupal chamber and swim to the surface before the adult emerges. The adults live for a couple weeks to a couple months and may diapause. Eggs are deposited in gelatinous strings or masses under water or near water.

Trophic Roles

Larvae assume most trophic roles, a few are sponge feeders. Adults take only fluids.

Communities

Often complex in all types of aquatic habitats with many species organized by habitat, trophic role, capture-net pore size, body size, altitudinally and seasonally. Many species appear rare in the benthos, many are highly clumped. A few species are semiaquatic living some distance from streams and ponds in damp leaf litter.

Cases And Nets

These are usually species and instar specific, but may vary somewhat with local circumstances. Tubular cases aid respiration and exploitation of lentic habitats.

Economic Importance

Important intermediate consumers in many streams, may replace mayflies and stoneflies in degraded waters. Important fish food, fishing fly patterns, water quality indicators, nets and cases may slow the flow in ditches and canals, sometimes an emergence nuisance especially at lights.

Zoogeography

A well studied and useful group. Many groups are plastic and rapidly evolving, while others are senescent with few relict species scattered in remnant habitats. Many adaptive radiations on islands. Northern and southern faunas are very different even at the family level.

Collecting

The best species list is made by collecting the adults at black light traps. The adults may also be swept from vegetation, netted from matting swarms, or picked from under bridges. Many larvae are taken in routine benthic samples, but many others are restricted to shoreline vegetation, burrow in wood, or in the muck around spring seeps. Larvae with heavy cases may be panned, some attach very strongly to surfaces.

Rearing

Usually associated via metamorphotypes- an advanced pupa contains the well formed adult as well as the larval sclerites in its cocoon. Young pupae may be reared in damp paper towels in a cool place until the adult structures form. Getting larvae to pupate is generally difficult.

Preservation

Larvae are best fixed in Kahle's fluid and transferred to 70% ethanol after a few days. Larvae may abandon their cases during preservation so keeping similar species separate is advised. Adults are collected and stored in 70% ethanol. A few pinned specimens are often useful as they retain their colors better.

Taxonomy

Species are best identified based on male genitalia. The abdomens must be cleared to see some of the details. For most species and some genera the larvae remain unassociated with the adults.

Synopsis Of Neartic Families

Southern hemisphere families Ecnomidae and Xiphocentronidae that occur as far north as Texas are omitted.

Spicipalpia + Annulipalpia)- case absent, or if present, not tube-like, either with only the pronotum sclerotized or with all three thoracic nota sclerotized and without dorsal or lateral humps on the first abdominal segment.

  1. all three thoracic nota are mostly sclerotized
    1. Hydropsychidae- abdomen with branched gills, build capture nets in rivers and streams
    2. Hydroptilidae- microcaddis, no abdominal gills, the last instar builds a purse case, common in streams, springs and lakes.
  2. only the pronotum is mostly sclerotized.
    1. dorsum of abdominal segment 9 is membranous.
      1. Philopotamidae- labrum membranous and T-shaped, clear streams of all sizes, filter feed on very small particles.
      2. Psychomyiidae- trochantin of foreleg broad and hatchet-shaped, build fixed retreats in cool streams.
      3. Polycentropodidae- trochantin of foreleg with apex acute, build fixed retreats in all types of waters, especially lake outlets, filterers and some predators.
    2. dorsum of abdominal segment 9 is sclerotized.
      1. Glossosomatidae- all instars build saddle-cases, anal claw with dorsal accessory hook(s), scrapers in streams of all sizes.
      2. Hydrobiosidae- free living predators, fore leg chelate, southwest warm streams.
      3. Rhyacophilidae- free living predators (mostly), fore leg normal, cold streams.
Integripalpia- case present and tube-like, may be flattened or coiled, most have the first 2 thoracic nota largely sclerotized, most have dorsal and lateral humps on the first abdominal segment.
  1. Helicopsychidae- anal claw comb-shaped, case coiled, scrapers in springs and warmer streams and lakes.
  2. Leptoceridae- long-horned caddis, antennae easily visible, length is at least 6 times the width, warmer lakes and streams.
  3. Phryganeidae- only the prothorax covered with sclerotized plates, lakes, ponds, swamps, bogs, and stream margins.
  4. Brachycentridae- abdominal segment 1 without any humps, streams of all sizes.
  5. Molannidae- hind tarsal claw different from the rest, lakes and rivers.
  6. Calamoceratidae- labrum with a transverse row of about 16 setae, mostly tropical, southern streams.
  7. Beraeidae- rare and local in eastern Usa spring seeps.
  8. Lepidostomatidae- abdominal segment 1 without dorsal hump, antennae close to eye, streams of all sizes.
  9. Limnephilidae- antennae halfway between eye and edge of head, prosternal horn present, common in all types of habitats.
  10. Sericostomatidae- antennae close to anterior edge of head, prosternal horn absent, fore-trochantin with hooked apex, streams and lakes.
  11. Odontoceridae- antennae close to anterior edge of head, prosternal horn absent, fore-trochantin without hooked apex, burrowers in streams.

Montana Species list

Key Reference

Reference Update

Other Sites

Updated on 23 NOV 1995 D.L. Gustafson
AIM home page
dlg@rivers.oscs.montana.edu