Learning Center

What Are Benthic Macroinvertebrates?

Hydropsychidae (common netspinner caddisflies)

Breaking down the terms:

Benthic = inhabiting bottom areas or substrates;

Freshwater = streams, rivers, lakes, ponds;

Macro = relatively “large” (> 0.2-0.5mm);

Invertebrate = animals without vertebrae (a backbone).

Putting it all together:

Benthic freshwater macroinvertebrates are animals without backbones, that are visible with the naked eye, living on the bottoms of streams, river, lakes, and ponds.

What Kinds of Macros Can You Find In a Stream?

Benthic freshwater macroinvertebrates, or “macros” for short, include crustaceans and worms but most are aquatic insects. Beetles, caddisflies, stoneflies, mayflies, hellgrammites, dragonflies, true flies, and some moths are among the groups of insects represented in streams.

Macros are an important link in the food web between the producers (leaves, algae) and higher consumers such as fish.

Common Stream Macroinvertebrates
Insects Crustaceans Annelids Mollusks
Stoneflies
Mayflies
Dragonflies
Damselflies
Hellgrammites
Beetles
True flies
Caddisflies
Crayfish
Scuds
Aquatic sowbugs
Aquatic worms
Planaria
Leeches
Clams
Mussels
Snails
Limpets

Insect Life Cycles

All insects go through a series of changes (metamorphoses) during their life cycle. Insect life cycles can be grouped as either complete or incomplete metamorphoses. A complete metamorphosis includes a pupae stage. The adult and larva tend to look very different from each other. Incomplete metamorphosis lacks the pupae stage and the nymph and adult are more similar in appearance.

Most aquatic insects remain underwater in the immature stages and leave the stream only as adults. The life cycles of macros can range from a few weeks to several years.

Aquatic Insect Life Cycles
Incomplete Metamorphosis Complete Metamorphosis
(Egg → nymph → adult)
Mayflies
Stoneflies
Dragonflies/Damselflies
True bugs
(Egg → larva → pupa → adult)
Caddisflies
Dobsonflies/alderflies
Beetles
True flies
Aquatic moths

What Do Macros Look Like?

Visit our Stroud Water Research Center’s photo gallery showing the 54 most common macroinvertebrates found during the course of our 12 year study of the Schuylkill River, or visit New York State Department of Environmental Conservation’s Key to Aquatic Macroinvertebrates.

To identify macros you have found, use Stroud Water Research Center’s online macroinvertebrate identification key.

« Back to the Learning Center