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Trichoptera (Caddisflies)

I. Background information


Trichoptera (Caddisflies) Trichoptera - Brigham Young/VPI & SU PCD0330076

A. Origin of name

  1. tricho, hair; ptera, wings
  2. refers to the setae on wings

B. Classification

  1. 21 families worldwide
  2. 1200 species in North America north of Mexico

C. Common names

  1. Caddisflies
  2. Other local names:
    1. Adults: Sedges, Shadflies, Sandflies
    2. Larvae: Caddisworms, Stick Bait, Rock Rollers

D. Type of metamorphosis

  1. Complete-holometabolous

E. Phylogenetic relationships

  1. Neopterous endopterygota

II. Morphological characteristics

A. Adults

  1. both wings membranous, covered with short hairs
  2. wings fold flat but held rooflike
  3. tarsi 4 or 5 segmented
  4.  mandibles greatly reduced
  5. long, many segmented antennae

B. Larvae

  1. thorax with three pairs of legs
  2. anal segment with pair of prolegs each bearing 1 claw
  3. short 1 segmented antennae
  4. eyes consisting of a single facet
  5. often in cases

III. Biological summary of the order

A. Life History Stages-Holometabolous

  1. Egg
    1. In some groups the female enters the water and cements the eggs to rocks, sticks, or water plants.
    2. Eggs are deposited in strings or grouped into irregular masses from a few to 800
    3. Individual eggs are surrounded by a thin cement-like matrix.
    4. In India a member of the Sericostomatidae was observed to enter a torrential waterfall and deposit its eggs on the lip of the falls. Most probably enter water in areas with less current.
    5. A member of the Hydropsychidae was observed to dive into the water from 2-3 feet and remained under a stone for 37 minutes while depositing 460 eggs. Air trapped in hairs apparently functioned in respiration.
    6. Families which enter the water to oviposit include Rhyacophilidae, Blossosomatidae, Psychomyiidae, Polycentropidae, Hydropsychidae and Hydroptilidae
    7. All other families, except Limnephilidae, generally deposit egg masses onto surface of the water.
    8. Eggs are always in gelatinous egg mass which may be colored greed or blue. *Some perch on rock or vegetation and protrude abdomen below surface (some females do go below surface).
    9. In those that drop egg masses, the gelatinous egg mass swells on contact doubling in size and becomes sticky. As it drifts downstream it attaches to a solid object. Generally 60-700 eggs in these.
    10. Limnephilidae deposit egg masses above the water on plants or stones. It is thought that the egg-mass swells during rainfall and that the young larvae are washed into the water.
    11. Philanisus (Chathalmidae-Australia & New Zealand)-lay eggs inside starfish
  2. Larvae
    1. Generally 5 to 7 larval instars.
    2. Almost all overwinter as larvae.
    3. Generally very little growth in winter
    4. Most rapid growth occurs before or after winter.
    5. Most construct case or net.
    6. Have silk glands with opening at tip of labium
  3. Pupae
    1. All pupae are protected by some type of cocoon.
    2. In case-bearing larvae the cocoon is created by closing the larval case and fastening it to a solid object.
    3. In some the case is shortened by cutting off one or both ends.
    4. Various ways of plugging cast: some pull in pieces of vegetation which also camouflage; some fill in opening with more silk which may be perforated to allow water to pass through; species inhabiting fast streams commonly plug opening with one or more stones.
    5. Net-spinning and free-living forms construct pupal case. Hydropsychids construct stone or sand case at their retreat. Free-living Rhyacophila construct case of small stones & fasten to stone with silk. Rhyacophila and Glossosomatidae secrete a tough membranous cocoon inside pupal case in which to pupate.
    6. When the case has been finished the last instar larva goes into a prepupal resting stage. Becomes stiff, shorter, broader. Head and abdomen lose their flexibility and intersegmental membranes became indistinct. Legs are in unusual positions (held at odd angles) characteristic of only this stage.
    7. Pupal stage generally lasts about 2-3 weeks
    8. Mandibles are large and function to cut out of case.
    9. Once out of case the pupae swim to the surface or objects at edge for emergence.
  4. Adults
    1. Fairly long-lived averaging about 30 days but some large species have been kept alive up to 105 days.
    2. Adults have reduced mouthparts adapted for obtaining liquid food (nectar), some are similar to the sponge of higher Diptera.
    3. Some summer species have short flight seasons. Emerge at one time between May-August. (Phryganeidae)
    4. Some summer species with long flight seasons. Individuals of some species commonly encountered continuously from May-September, due to steady emergences. (Leptoceridae, Hydropsychidae, Polycentropodidae, Hydroptilidae)
    5. Autumn species only emerge from September-November, Limnephilidae-3 months with diapause during late summer and early fall.
    6. Most Trichoptera have 1 year life cycle. Some smaller species produce more than 1 brood per year and some larger species in colder climates may require more than 1 year to develop.

B. Habitat

  1. Found in all habitat categories.
  2. All sizes of these categories.
  3. Seeps, springs, streams, rivers, lakes, marshes, temporary pools.
  4. All families found in cool, lotic waters.
  5. Thought to have evolved in small, wooded mountain streams.
  6. Fewer families in larger, warmer bodies of water.

C. Habits

  1. Clingers, climbers, sprawlers
  2. In most, habits are closely associated with use of silk to make cases and retreats.
  3. Categories of net and case-making
    1. Free-living
      1. no case or shelter
      2. predaceous
      3. deposit a thread trail
      4. strong legs and well developed anal hoods
      5. Rhyacophilidae and early instars of Hydroptilidae
    2. Net-spinning
      1. spin nets, snares, and webs of silk in which to live and trap food
      2. fixed dwellings, not portable
      3. Hydropsychidae
      4. Finger nets
        1. long narrow pockets of fine mesh with the front end anchored upstream, the remainder trailing behind in the current
        2. Philipotamidae
      5. Trumpet nets
        1. tube with opening funnel shaped and fastened so that current distends net into trumpet shape.
        2. Polycentropidae
      6. Amorphous silk galleries
        1. silk dwelling with many silk fibers stretching and irregularly to trap prey much like spider web.
        2. nets often covered silt and debris
        3. occur in still water
        4. Polycentropidae
      7. Hydropsychid net
        1. large net constructed in front of a tubelike retreat concealed in a crevice or camouflaged by bits of wood or leaves.
        2. always in some degree of current
        3. larvae periodically clean off the food trapped on the net
        4. Hydropsychidae
      8. Tube-making
        1. construct branching tubes in sediment
        2. tubes are silk and sediment and are rigid enough to be removed intact
        3. larvae bring in food by undulating body
        4. Phylocentropus (Polycentropidae)
      9. Case makers
        1. larvae construct portable dwellings of silk and various materials such as sand, stones, leaves, algae, or sticks.
        2. some are open at both ends so that the thoracic legs and anal prolegs are in contact with substrate Blossosomatidae and Hydroptilidae.
        3. most are only open at one end
        4. the head and thoracic legs project from the opening and the larva drags the case with it
  4. Trophic relations: broad, generally regarded as omnivorous. Live plant material seldom eaten.
    1. Collector-gatherers
    2. Collector-filterers
    3. Shredders
    4. Scrapers
    5. Engulfers
  5. Since they often occur in large numbers in a variety of niches, Caddisflies are presently receiving a lot of attention in regard to their role in the flow of energy through ecosystem. Some take large particles and make them available as smaller and visa versa. Generally show little selectivity of food that becomes available but highly specialized in manner and location in which food is obtained.

D. Methods

  1. Collecting
    1. Larvae and pupae-correct habitat under stones and logs in riffles, aquatic vegetation, leaves, in stream or pond. Pupae generally attached to solid objects.
    2. Adults
      1. lights-black, Coleman lantern, porch, auto
      2. aerial net-sweep foliage or capture swarming
      3. under bridges
  2. Preserving
    1. Adults-70% alcohol for most purposes. Some groups must be pinned to preserve color patterns.
    2. Larvae and Pupae-70% alcohol. Change within 1 week. Killing in boiling water and then placing in alcohol produces well extended specimens facilitating identification.
  3. Rearing
    1. To associate larvae with adults, one must isolate larvae in cages.
    2. Usually aeration provides sufficient oxygen and current. Some (e.g. Hydropsychidae) require unidirectional current. Some type of flowing system.
    3. Larval sclerites are usually easy to find because they are left in the pupal case.
    4. Pupae may be as good as adults because in mature pupae the adult genitalia can be dissected out from inside of pupa.
    5. Easier to collect pupae in field than rear.
  4. Preparation for study
    1. Adults
      1. Male and sometimes female genitalia clipped off and cleared in KOH to remove tissue and allow visibility. Small specimens cleared intact. Genitalia placed in very small vial containing glycerine. Genitalia vial placed in alcohol or put on pin under specimen.
    2. Larvae-none

E. Behavior

  1. Males form swarms for mating, but not as spectacular as mayflies
  2. Some larvae defend territories
    1. stridulation
    2. aggression

F. Significance

  1. Adults
    1. allergic
    2. nuisance
  2. Larvae
    1. one of the most abundant aquatic insects
      1. Cheumatopsyche cempyla in New River
        1. average density: 22,000/ m2
        2. maximum density: 47,000/ m2
      2. All net-spinners in North Anna River
        1. production (dry weight):
          325,000 mg/m2
          3.250 kg/m2
          0.715 lbs/m2
          7150 lbs/ha
          weight weight = 6x dry weight
    2. probably have significant functions
      1. prey for fish
      2. alter size and quality of detritus
        1. shredders: smaller and qualityc
        2. collector-filterers: same size or larger and quality

Insect Identification and Diagnosis Request

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