Stream Insects at Powdermill

Powdermill Nature Reserve has begun their monthly series of nature talks, "Science and Nature Program/ Nature Explorers".  It's two events that happen simultaneously, a science talk for teens and adults, and a nature class for kids 8-13. Both indoor programs are followed by a short walk outdoors to observe the subject of the programs. We attended the April event, on "Aquatic Entomology". It was terrific!

A demonstration of the kick net.

We became fascinated with aquatic critters when my son was only 3, and we attended a homeschool program that included a simple activity where kids dipped nets into a pond and inspected what they caught. I was frankly shocked to discover the sheer volume of life per square inch in a body of water, and that's just what can be seen with the naked eye! Since then, we've attended lots of environmental education events that have included learning about these animals. For years I kept a Brock microscope, some nets and a jar in my trunk so that if we found ourselves near a pond or stream, we could take a close look at what we might find and try to identify our animals. So we knew a bit about this subject already.  But their presenter, Powdermill research entomologist Andrea Kautz, taught us more in a brief talk than all we've learned so far. Ms. Kautz has been capturing and imaging aquatic insects for a very cool website, Macroinvertebrates.org, which has startling close-up images of these strange, alien beasties. You can zoom in on them and read about individual features of their bodies. So she knows what she's talking about.

She explained that there are two main methods for assessing the health of a stream, each with pros and cons. The first method is to test water quality, which would include temperature, dissolved oxygen, pH, chemistry, etc. The results are precise and easy to collect, but they fail to capture fluctuations that can be devastating to aquatic life.  For example, a factory might release hot water into a stream and quickly kill off many animals, without leaving much of a trace. The second is to survey the aquatic life itself. She described a rating system given to aquatic macroinvertebrates that pinpoints the sensitivity each species has. A really healthy stream should have a good diversity and volume of life, and the presence of especially sensitive species would be a positive indicator. 

There are lots of kinds of macroinvertebrates that live in our rivers and streams, while in their juvenile forms. Aside from many kinds of insects, there are crustaceans, mollusks, worms and more. But the ones that scientists especially like to see are "EPTs". This stands for Ephemeroptera (mayflies), Plecoptera (stoneflies) and Trichoptera (caddisflies). I've always found these critters hard to identify. She gave us some excellent tips. Mayflies usually have 3 tails, sometimes 2. They also have feathery gills on their sides, and single claws. Stoneflies have 2 tails, and their gills may be visible on their undersides, or may be hard to detect. They also have double claws. She said that she is always pleased when she finds giant stoneflies in a stream. They are pretty neat animals, and quite picky about water quality.

Caddisflies are famous for the houses they construct for themselves, which shelter and protect them.  They make a silk which is used as a strong glue for holding their house together. What I didn't know is that they can, and do, run around outside of their houses, and some don't build them at all. Of the house builders, each species has a preference of building materials which can vary as they age. The conical homes may be started when the caddisfly is small, and enlarged as it grows, much like a snail shell. Or they might just start over and build a larger home. The variety of homes and building methods is truly astonishing.  They may use pretty much anything they find in the water, including leaves, twigs, sand, snail shells and gravel. The gift shop at Powdermill has quite a few pieces of jewelry made by caddisflies that were presented only with small semiprecious stones, gold, etc. with which to make their homes. 

Afterwards, we went outside to the creek to see what we could find in the water. Ms. Kautz showed us how to use a kick net to catch critters, and she put the resulting collection in shallow white bins for investigation. This is the quick way to find what's living in a stream. The slow method is to put an artificial substrate in the water and come back later to find out what's been colonizing it. Judging from the variety we found, I'm guessing it's a pretty healthy stream!

This was the teensiest crawdad I've ever seen. It wasn't until I looked at the photo
that I discovered it was helping itself to a snack from the multitude of tiny insects that were caught.

Mayfly.

Stonefly.

Stonefly.

Caddisfly.

A larger crawdad.

This caddisfly was up to something...

I think it was picking out debris in the bin...

...and starting to build a new house.

Caddisflies with twig homes.

A caddisfly at home.

A caddisfly without a home.

A lovely green caddisfly.

Mayfly.

Caddisfly.

The day we visited Powdermill, no wildflowers were blooming there except the infamous skunk cabbage. Skunk cabbage is truly freaky. It doesn't mind the weather because it generates its own heat! (I guess it's warm blooded?!?). It can be nearly body temperature in the dead of winter, at 95ºF, so that it can grow through frozen ground and spread its scent far and wide. To us, it smells like a skunk, but apparently to flies it smells like a rotting carcass. They come running for a tasty treat, and instead become the plant's pollinators. 

Skunk cabbage.

Skunk cabbage.