Bentic Macroinvertebrates

Does the title of this post sound like Greek to you? Simply put, benthic macroinvertebrates are little tiny bugs that live in our waterways, but you are able to see them with your naked eye. They are often the larvae of insects that we are more familiar with like blackflies, mayflies, and more! While ponds and lakes do have some, there is a higher number of species found in running waterways. And they can actually tell you a lot about the water that they live in! Many agencies use them as a measure of water quality. In a nutshell, some species are more tolerant of pollution than others. So you collect insects for a certain amount of time, count how many are pollution tolerant, pollution sensitive and pollution intolerant, and then do some easy math! You can also calculate what is called an EPT index. This is based on how many mayflies (Ephemeroptera), stoneflies (Plecoptera), and caddisflies (Trichoptera). This is great if you have a stream running on your property and want to know more about its health.

Because there are so many species, typically macroinvertebrates are broken down into families or orders. A dichotomous key is very helpful in their identification. In West Virgina alone, there are 538 species that the state has identified! This level of identification is hard without breaking out a microscope. In high school, I volunteered with a stream team that was partnered with a local university. We would go out and collect the samples and analyze them. While the EPA does have an SOP for sampling macroinvertebrates most state agencies have their own SOP which can be found by simply googling XYZ State macroinvertebrate sampling. I’m basing the rest of this information on the Georgia EPD SOP. These SOPs are similar to the EPA’s SOP but are adapted to be more effective based on the eco-region. I will detail how to conduct surveys in a future post but for now, let’s look at the different groups of macroinvertebrates.

I haven’t quite figured out how to put pictures on the blog but these websites have great images and I included some drawings that I drew myself. has good images of mayflies, stoneflies, and caddisflies This gallery really breaks down the different types of macroinvertebrates

  • Order Megaloptera: dobsonflies and alderflies
    • Family Corydalidae
      • intolerant of pollution
      • they are a predator species
      • often called hellgrammites and used for fishing
    • Family Sialidae
      • similar to the dobsonfly but smaller
      • also a predator
  • Order Ephemeroptera: Mayflies
  • stonefly
    • widespread and abundant
    • adults only live 24 hours
    • important food source for fish
    • have a range of pollution tolerance
    • most have 3 tails (called caudal filaments) but some have 2 tails
      • Families include Baetidae, Caenidae, Ephemerellidae, Ephemeridae, Heptageniidae, Isonychiidae, Leptophlebiidae, and Tricorythidae
  • Order Trichoptera: caddisflies
    • there are 3 main types: free-living, case-building, and net-spinning
      • the case-builders have a protective case that they build out of whatever they find in a stream
        • the families of case builders include: Helicopsychidae, Leptoceridae, Hydroptildae
        • there is actually a lady who sells jewelry made out of their casings (
    • have three pairs of legs near the head (called thoracic legs) and the body kind of looks like a little caterpillar
    • have a wide range of pollution tolerance
  • Order Odonata: damselflies and dragonflies
    • these are actually really aggressive aquatic predators in their larval stage!
    • most of their diet is made up of mosquitoes
    • the suborder Anisoptera have a spoon-shaped mask over their face
    • tolerate some pollution
  • Order Plecoptera: stoneflies
    • mayfly
    • intolerant to pollution
    • look similar to mayflies but often only have 2 tails
    • because of their lack of gills they need a stream with high oxygen levels since water can hold more oxygen the colder it is, they are associated with cool mountain streams
  • Order Diptera: true flies
    • larvae are legless
    • don’t have a well-developed head
    • very tolerant of poor pollution
    • families include
      • Simulidae: black flies
      • Tipulidae: craneflies
      • Tabanidae: deerflies and horseflies
      • Chironomidae: midges
      • Culicidae: mosquitoes
      • Syrphidae: rat-tailed maggots
  • Order Hemiptera: true bugs
    • both the adults and larvae are aquatic
    • Families
      • Belostomatidae: Giant water bugs
        • very large insects
        • eaten in Asian cuisine
        • have a very painful bite, they liquefy the insides of their prey
          • I witnessed this 1st hand when I put one in my fish tank, having no idea what it was
          • 120731_0000
      • Corixidae: Water Boatman
        • very common in pools and swimming pools
        • cling to submerged vegetation
        • do not bite
        • feed on algae
      • Gerridae: Water Striders
  • Order Coleoptera: beetles
    • the largest order of insects
    • have chewing mouthparts
      • Families
        • Dytiscidae: predaceous diving beetles
          • larvae and adults are aquatic
        • Elmidae: Riffle beetles
        • Psephenidae: water penny
        • Waterpenny
  • Order Lepidoptera: aquatic caterpillars
    • these are species of butterflies and moths that are aquatic as larvae
    • it’s really hard to tell the difference between species that are truly aquatic and terrestrial

In addition to those orders, there are also segmented worms (phylum Annelida), crustaceans (including crayfish and mussels), sowbugs, and water fleas. I used to work in a freshwater mussel lab and will do another entire blog post on mussels. They really are fascinating creatures, and all Unionids even have a stage of their life cycle where they live on the gills of fish! Well, the Salamander Mussel is an exception. They have a stage where they live on the gills of salamanders.







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