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 Macroinvertebrates 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
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)
|(Egg → larva → pupa → adult)
What Do Macroinvertebrates Look Like?
Visit 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 the Stroud Center’s online macroinvertebrate identification key.