Other Macroinvertebrates

The larvae, nymphs, and pupae of mayflies, stoneflies, caddisflies, and true flies turn up in great numbers in stream samples. But there are other macroinvertebrates that you can see (especially with a magnifying glass), and each species has something to tell you about the health of your stream.

In the Phylum Arthropoda ("jointed legs") and the Class Arachnida are the water mites, called Hydracarinae (after their Family). Their little bodies are spherical and hard, and of course they have eight legs like their cousins, the spiders. It would be easy to miss these in a sample, since they look a little like particles of sand.

In the same Phylum but in the Class Insecta we find not only all the insects mentioned above, but also several other orders. Hemiptera (true bugs) include backswimmers, water boatmen, and water striders, all of which are pretty easy to identify.

riffle beetle	water penny		hellgrammite
Coleoptera (beetles) include riffle beetles and water pennies, whirligig beetles, and diving beetles. Many of the beetles you find in a stream sample will be in larval form.			There are also the Megaloptera, which include the hellgrammites (dobsonflies). These are big predators that you will need no magnifying glass to see! They can even bite you, so be careful.
dragonfly	damselfly		seed shrimp
The Odonata are the dragonflies and damselflies. They may look elegant in flight, but their larvae are fierce predators, with enormous mouthparts that shoot out to catch prey.			Ostracoda (seed shrimp) are in the Class Crustacea (which are cousins of Insecta because they, too, have jointed legs). These actually look like tiny seeds. If you look closely enough at one, you might see its feet protruding from its "shell." These strange animals have seven pairs of legs.
scud	sowbug		crayfish
Amphipoda (scuds), and Isopoda (sowbugs) are other insects sometimes seen in samples.			The Decapoda (crayfish) have ten legs, as you can tell by their name. They are in the Class Crustacea. They form an important part of the diet of many people around the world.
	fingernail clam	snails
	In a completely different phylum from all these are the molluscs, in Phylum Mollusca. These include Bivalvia (fingernail clams) and Gastropoda (snails), both extremely tiny.
oligochaete	leech		flatworm
The Phylum Annelida includes aquatic earthworms (Class Oligochaeta: "oligochaetes," which include Tubifex worms) and leeches (Class Hirudinea).			In the more "primitive" phyla we find flatworms (Planaria) and nematodes (Nematoda).

Scientists and activists use stream invertebrates, because they are numerous and easy to collect, to help them gauge the health of streams. To learn more about macroinvertebrates, check out the reading list, where you will find some excellent references listed. (You will be able to order them from here, too).

• Identification
  Aquatic Macroinvertebrate Identification Key Online, completely automated key
  Key to Aquatic Macroinvertebrates (all macroinvertebrate taxa, with excellent photos)
  Key to Macroinvertebrate Life (chart developed by Univ. of Wisconsin-Extension)
  (PDF file - requires Acrobat Reader)
  
  Aquatic Invertebrate Identification (some beautiful photos and drawings)
  

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