The secret lives of streams
Ever feel the urge to jump in a stream and maybe even pick up a rock or two and see what small creatures might be living there? If you do, then I can guarantee that you will find a highly diverse community of benthic macroinvertebrates, better known as aquatic insects. What exactly are these things? They are small, sometimes only a few millimeters in length, larval versions of mayflies, butterflies, blackflies, and more. These organisms can live as many as 3 years or more beneath the surface of streams, rivers, and wetlands. In fact, they carry out the majority of their life stages in the benthos of aquatic ecosystems, only to emerge from their final instar (which is the last molting stage before the larvae become sexually mature adults) as the winged bugs we are use to seeing. In a strange fate of biological form and function, the adult stages of stoneflies and mayflies is extremely short: most only have between 24 to 48 hours to find a mate before they literally drop dead. It's sad but it works, since these organisms, especially maylfies, are some of the most ancient of insect orders, with fossils dating back to the Devonian Period. Their life cycles are something to be in awe of, since most of their lives are spent as developing larvae, which are useful for ecologists for biomonitoring of streams and wetlands.
What is biomonitoring? It is the use of a biological community in order to assess the health of streams and other bodies of water. In reality, this method of quantifying the impact of agricultural pollution, waste treatment plants, and other sources of pollution on a stream is a "snap shot" of the health status of that stream or section of the stream. When I took Ecology in the Fall 2012, we put our waders on, jumped into several sections of different streams, and used a large D-net, which is a standard mesh net used for collecting small organisms, and we caught a sample of the members of the biological community at a specific time. To put all this biomonitoring in perspective, here's an example. Say you spent 5 minutes netting for macroinvertebrates, and you have your sample on a tray for all to see; you have before you several species of stoneflies (Order Plecoptera), mayflies (Order Ephemeroptera), dragonfly larvae (Order Odonata: Anisoptera), and a caddisfly larvae (Order Trichoptera). After looking at your pretty diverse sample, you could say your section of the stream is not impacted by pollution.This is because the presence and absence of key insect orders, namely the stoneflies, serve as keystone indicators of pollution levels. Stoneflies are among the most pollution-sensitive organisms, so if you come across them, consider yourself lucky! Not only are stoneflies beautiful with their ornate designs on their body surface, but they are particularly fussy about dissolved oxygen levels and have specific habitat requirements. Mayflies and caddisflies are also pollution sensitive, and rarely will be found in streams that are severely impacted by organic pollution and storm water runoff.
So, about those bugs under the rocks in the water? They might be small, inconspicuous, and otherwise not important to you personally, but they play a vital role in stream ecosystems and help biologists and ecologists monitor water quality, which ultimately matters to us in the end.