Have you ever wondered what it would be like to shrink down to the size of an insect and navigate the world? What would you eat? What would you do? How would you feel? Would you feel love? Would you think about what you have to do tomorrow? Would you look at your reflection in a pond and wish you had prettier wings (I doubt it)?
Is it just me?
Well, some of these questions have answers. And today, I want to shrink down and take you through the day (and life cycle) of my favorite aquatic macroinvertebrate: the Stonefly. First, let’s back up. If you fumbled over that long word - macroinvertebrate - you’re not alone. Breaking it down piece by piece, the prefix macro means “large”- large enough for the naked eye to see. Microorganisms, by contrast, require a microscope to see. Humans and animals have vertebrae, which are bones that make up a spine. Here, we are talking about in-vertebrates, meaning they don’t have a hard skeletal structure. Think about the last time you stepped on a spider– did you hear a squish or a crunch? Invertebrates lack a skeletal structure, relying on a hard outer layer called an exoskeleton that protects their body– although it won’t hold up to a human foot!
[For the record, spiders are really cool and if you can transport them elsewhere without making your shoe a murderer, I would recommend it.]
Let’s get back to stoneflies. This family of macroinvertebrates, genus Plecoptera, is one of the coolest bugs you can find in our rivers and streams. They are often used as an indicator species as their presence indicates high water quality. Whenever we find one of these at a project site, we are always excited (and if it’s me, I’ll show it to anyone I can find – ask my friends and family). When assessing water quality, biologists often sample invertebrates over a period of time to help determine water quality and habitat suitability. There are three families that are considered excellent water quality indicators, known to us as the "EPT" species. Those are Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies). These species are extremely intolerant to pollution, so their presence is a great sign that pollution levels are low. All of these species spend their nymph, or juvenile stage, in aquatic systems. Typically they are found in fast moving streams with plenty of rocks and logs for cover. Eventually, they emerge as adults and fly upstream to lay eggs and begin the process again.
Life Cycle
Stonefly nymphs have between 10-30 development stages, commonly called instars. They spend their nymph stage in the water for 1 to 4 years, shedding their exoskeleton between stages before emerging and becoming terrestrial flying adults. To find a mate, they crawl onto vegetation or rocks, and males drum their abdomen to attract females via vibrational signals. Female stoneflies can lay up to one thousand eggs, dropping the sticky eggs in water to attach to rocks and branches. Adults are weak flyers and typically stay close to the stream they hatched from, surviving only a few weeks to fulfill their reproductive strategy.
A stonefly larvae in its final instar. This is about as big as they get!
Feeding strategies are somewhat variable, but for the most part they eat microorganisms and small plant matter that hosts bioavailable organic materials and nutrients that allow them to grow.
Many of these nymphs won’t make it to the adult stage. They are a delectable protein treat for fish, birds (especially waterfowl), small mammals, and larger aquatic organisms. If you find any aquatic invertebrates, make sure you return them to the water (after you’ve taken a picture) to keep the food chain intact.
Identification 101
You can identify stonefly larvae without much equipment (and it’s a really fun outdoor activity for kids)! First, you have to find one. One of the easiest ways to find these species is to look for submerged rocks. They tend to like bigger rocks- at least the size of your hand. Gently lift the rock and flip it over, watching carefully for squiggly, dark, blobs. They blend into rocks very well as protection from predators, so you may only be able to see a wet, moving object between 1-5 cm long. From here, you can gently use a pair of tweezers or brush the bug off the rock into a bucket of water. This allows you to see their features while keeping them safe and wet as they would normally be in their aquatic environment. I recommend a white bucket or Tupperware with a white piece of paper below for the best viewing opportunities.
If you have access to a small handheld net, that can also be a great tool to find some bugs. Try to scoop them along the edge of the water where there may be vegetation partially submerged. You can also hold nets on the bottom of the river bed and gently kick the substrate upstream to try and release invertebrates from underlying sediments. The options are abundant!
YouTube videos: Golden Stonefly Nymphs, How to Catch Aquatic Insects
Stonefly anatomy diagram showing general features and traits. Juvenile stoneflies are typically tan, brown, or black to best hide from in-stream predators.
Dichotomous Key
Identification can be done fairly easily using a dichotomous key, which is essentially a flow chart you can follow to identify an organism. First, you want to see if the organism has a shell or hardened exterior (like a crayfish or snail). Next, move down the diagram and answer “yes or no” questions regarding legs, wings, and tails. Eventually, you can identify at the bottom and confirm with the likeness of the graphic.
The trademark of a stonefly is that it has two tails- called cerci. Note, mayflies have three tails, so look carefully!
Examples of dichotomous keys from Ausable River Association & Ripple, the center for education and ecosystem studies. The colored dots indicate tolerance to pollution, which is why macroinvertebrates are commonly used to access water quality (you can get a lot of information from presence/absence).
Don’t be intimidated by these tiny bugs! Anything smaller than a crayfish has no ability to hurt you. Wading in creeks is a great way to connect with nature- even if you don’t find any macroinvertebrates. A Bug's Life series will continue, so check back for more in depth profiles on cool aquatic macroinvertebrates in the Rogue River Watershed.
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