Food Webs & Functional Feeding Groups

Since the late 1970s, insect groups in streams have been classified into Functional Feeding Groups rather than the standard trophic levels. This food web scheme was adopted because many insects in streams eat across several trophic levels making the trophic level classification system not very useful in describing these food webs.

The Functional Feeding Group classification system groups aquatic insects in terms of both how and what they eat. There are 6 major Functional Feeding Groups (see table below). Classifying aquatic insects by how and what they eat is a useful way to introduce insects to your students without having to know the names of the animals.

Functional Feeding Group

What do they eat?

Where do they fit in the standard food web?

What examples of stream insects are in this group?

Shredders Large pieces of living and dead plant material (Coarse Particulate Organic Matter [CPOM]) Some Herbivores; some Detritivores Some stoneflies, caddisflies, beetles, and flies
Collectors Small pieces of dead decomposing plant material and feces from other organisms (detritus); Fine Particulate Organic Matter (FPOM)) Detritivores Some mayflies, caddisflies,
flies, and beetle
Scrapers Periphyton- algae and associated material attached to rocks and other substrates Herbivores Some mayflies, caddisflies, beetles and flies
Piercers of Plants Living plants or cells of  filamentous (macroscopic) algae Herbivores Some spongilliflies, dobsonflies
and caddisflies
Predators Living animals Carnivores Some stoneflies, dragonflies,
dobsonflies, beetles, and flies
Parasites Living animals Parasite Wasps and Flies

Adapted from table 6C, Merritt et al. 2006


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The MSP project is funded by an ESEA, Title II Part B Mathematics and Science Partnership Grant through the Montana Office of Public Instruction. MSP was developed by the Clark Fork Watershed Education Program and faculty from Montana Tech of The University of Montana and Montana State University, with support from other Montana University System Faculty.