Insects that live in the stream, known as stream invertebrates, are an excellent way of determining the health of a creek or river. The reason for this is that different types of insects prefer to live in different types of stream conditions. Some prefer cleaner water while others may be more "tolerant" to adverse conditions. So, by looking at the type of insects living in a stream, one can tell how healthy the water source is. For example, larvae of caddisflies, mayflies, and stoneflies will only live in clean oxygen-rich water, which also happens to be favourable for salmon. On the other hand, aquatic worms are more tolerant to polluted oxygen-deprived systems. Knowing this, we can sample the insects in a stream, and by simply determining which species are present, we can learn if the waters will be favourable for coho and other salmonids. Most aquatic insects will grow through the majority of their life cycles under water. The egg to the larva and pupa stages, and the egg to the nymph stage (nymphs are miniature adults), all take place underwater. Their adult stage, which often only lasts a couple of days, is spent in the air - usually these are the insects one sees flying around the creek.

Water Skeeters

The four main classifications of invertebrates are ‘Shredders,’ which eat rough organic material, ‘Collectors,’ which eat the finer organic materials, ‘Scrapers,’ who feed from the stream’s bottom, and ‘Predators,’ which will feed on just about any small insects. All of these classifications have slightly different feeding patterns and life cycles.

The importance of insects in any system should never be underestimated. Many invertebrates feed on algae, bacteria, fungi, and leaf litter as the first part of their role in the food web. These insects then go on to feed other insects and predators, continuing the food chain. Most of these insects and predators are a preferred food source essential to a growing salmon. So next time you brush a mayfly off your arm, just remember that its babies might be a coho’s supper.

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