Identifying orders of aquatic macroinvertebrates
The Stroud Water Research Center in Pennsylvania has an excellent quick key to order. The photographs below represent the most common organisms we encounter in each major group.
Latin names for the orders link to the Tree of Life. Characteristics listed below are for the immature life cycle stages typically found in aquatic habitats.
Ephemeroptera : Mayflies
- 3 (or less commonly 2) "tails" (cerci)
- 1 claw per foot
- Families: Baetidae, Caenidae, Ephemerellidae, Heptageniidae, Isonychiidae, Leptophlebiidae, Siphlonuridae
Plecoptera : Stoneflies
- 2 "tails" (cerci)
- 2 claws per foot
- Families: Capniidae (Capnia and Nemocapnia), Chloroperlidae, Leuctridae, Nemouridae, Peltoperlidae, Perlidae, Perlodidae, Pteronarcyidae
Trichoptera : Caddisflies
- 3 pairs of jointed legs
- 1 pair of anal claws
- Frequently in cases
- may be present as pupae
- Families: Apataniidae, Brachycentridae, Glossosomatidae, Helicopsychidae, Hydropsychidae, Hydroptilidae, Lepidostomatidae, Leptoceridae, Limnephilidae, Odontoceridae, Philopotamidae, Polycentropodidae, Rhyacophilidae, Uenoidae
Diptera : True Flies
- jointed legs absent
- but there may be 'prolegs'
- may be present as pupae
- Families: Athericidae, Blephariceridae, Ceratopogonidae, Chironomidae, Psychodidae, Sciomyzidae, Simuliidae, Tipulidae
Coleoptera : Beetles
-There are no obvious characteristics to simplify identification of this group so we have provided the following pictures of the common beetles we find; the last 4 photographs represent beetles more commonly found in ponds (click to enlarge):
- Families: Dytiscidae, Elmidae, Gyrinidae, Haliplidae, Hydrophilidae, Psephenidae
Odonata: Dragonflies and damselflies
-Members of both suborders have hinged labial masks underlying their heads.
-Anisoptera: Dragonflies are distinctly robust with bodies typically as wide or wider than their heads
- Families: Aeshnidae, Gomphidae, Libellulidae
-Zygoptera: Damselfly bodies are slimmer than their head width and have three leaf-like gills on their tail end. The gills sometimes break off, but the stumps are usually visible under a microscope.
- Families (one so far): Coenagrionidae
Megaloptera: Dobsonflies, alderflies, and fishflies are predatory insects with paired lateral filaments on each abdominal segment.
Dobsonflies (family Corydalidae) have 2 pairs of anal claws and were the most common megalopterans in our samples.
This image from wikimedia commons
Anal claws are lacking in the alderflies; a single prominent caudal filament or 'tail' distinguishes the alderflies from most other macroinvertebrates.
Lepidoptera: This is probably our least-frequently encountered insect order. We do some times find aquatic moth larvae and they are characterized by paired ventral prolegs that each end with a tidy ellipse of tiny hooks or crochets. True jointed legs are also present on the thorax as indicated by the arrows in the photograph below.
Non-insects: A number of non-insect macroinvertebrates are common in our samples.
Isopoda: Isopods have 7 pairs of walking legs and are flattened top to bottom (dorso-ventrally).
Amphipoda: Closely related to the isopods, the amphipods are flattened side to side.
-Families: Crangonyctidae, Gammaridae, Hyallelidae
Collembola: Springtails are non-insect hexapods. They have a distinctive ventral tube on the first abdominal segment. Because the rear legs tend to sweep back, the tube frequently appears between the last pair of legs. A forked spring mechanism (furculum) typically points back in preserved specimens, but sometimes remains held under the body. Click on the thumbnail image for a close look. Commonly encountered families include Entomobryidae, Isotomidae, and Sminthuridae.
Mollusca: We frequently find snails (Gastropoda) in streams and common examples are pictured below. The last two photographs represent invasive bivalve mollusks. Zebra mussels are found in lakes; Asian clams have been sampled by our partner schools in the Bronx and Puerto Rico.
|Feedback - Partner schools: send us specimens not included above. Taxonomists: click to email: Declan McCabe|
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