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Macroinvertebrate Assemblages of the Skagit River

Functional Feeding Groups of Macroinvertebrates

Macroinvertebrates are often organized in guilds based on their feeding habits. The guild structure in a stream will reflect the overall health of the stream. Typically, polluted streams see a decline in CPOM/FPOM shredders and collectors dependent on allochthonous inputs, and a rise in scrapers and collectors dependent on autotrophic energy inputs.

Functional Feeding Group

Dominant Food Source

Feeding Mechanisms



Periphyton attached algae (diatoms) and other material growing on substrates

Herbivores grazing scrapers.

Trichoptera, Ephemeroptera,




Living plant tissue

Herbivores chewers, borers, gougers.



Coarse particulate organic matter (CPOM)

Detrivores chewers, borers, gougers.

Trichoptera, Tipulidae,

Plecoptera, Crayfish

Decomposing plant tissue and wood (>1 mm)



Decomposing fine particulate organic matter (FPOM)

Detrivores gatherers, deposit feeders.

Detrivores filterers, suspension feeders.

Trichoptera, Diptera

Ephemeroptera, Diptera, Chironomidae


Prey other invertebrates

Carnivores attack prey, pierce tissues and cells, suck fluids.

Carnivores ingest whole (or part of) other organisms.


Megaloptera, Odonata

Macroinvertebrates Tolerance Groups to Eutrophication

Group I; Pollution Intolerant, Sensitive to Pollution

  • Trichoptera (caddis fly)
  • Megaloptera, Corydalus (hellgrammites)
  • Ephemeoptera (mayfly)
  • Gastropoda (gilled snails)
  • Coleoptera, Elmidae (riffle beetles)
  • Plecoptera (stonefly)

Group II; Somewhat Pollution Tolerant

  • Coleoptera (other beetles)
  • Pelecypoda (clams and mussels)
  • Pisididae (fingernail clams)
  • Turbillaria (flatworms or planaria)
  • Diptera, Tupulidae (Cranefly)
  • Crustacea (crayfish, scud, sowbug)
  • Hemiptera (water boatman, backswimmer, toe biter, water strider)
  • Odonata (dragonfly, damselfly)
  • Megaloptera, Chauliodes & Sialidae (fishfly, alderfly)

Group III; Pollution Tolerance High

  • Oligocheta (worms)
  • Diptera, Simulidae (blackfly)
  • Hirudinea (leech)
  • Diptera, Chironomide (midge, bloodworm)
  • Gastropoda (other snails)