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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)