Truckee River Entomology

This last week I've been working with my my eldest son on his 1st grade science project and what better topic to choose than Entomology...its a great basis for fly fishing. Not only is it educational, its something he really enjoyed (unlike when I take him fly fishing, he's bored if he doesn't have a fish in 5 minutes). This month is a great bug month, especially with the Truckee River flows being so constant...the one good thing about a lousy water year. This may be a bit basic for some of you avid river bums (after all, it was for a 1st grader), but I thought these seine net samples did a good job at showing a typical cross section of the abundant Truckee River invertebrate biomass.

As you'll see, I quote and link to many great sites from which I pulled much of our information. Lets start with the insects which undergo a complete metamorphosis (meaning their life cycle has 4 stages: egg, larva, pupa and adult):

Midges (includes animals in several families of Nematoceran Diptera; we looked at component family Chironomidae, aka non-biting midges)

To me, these two-winged flies are the most under-appreciated insect in the Truckee and especially in the Little Truckee. Its an important staple for trout in this area and carries fish over the lean winter periods because of its prolific numbers and year round hatches. When nothing seems to be hatching, I go midge'n. "In North America there are over two thousand species; in Britain there are at least 430; while there are over 600 species in mainland Europe; over 200 in Australia; and even more the world over. Where they are found, the midges form at least 50% of the aquatic insect population. In rivers midge can outnumber the 'mayflies' by as many as four times. Since the early part of 20th Century entomologists have gained a detailed understanding of these insects; knowledge which anglers have not ignored. The midge's lifecycle includes a full metamorphosis. Starting as eggs they hatch out as larvae and then have later phases as pupae and then adult." Above is a picture of an adult and a larva; they number in the thousands on any section of water on any given day.

Caddis (Order Trichoptera, we looked larvae of "free-living" Rhyacophila family including sedges and also found "saddle-cased" or Glossosoma family)

"Commonly known as caddisflies or sedge flies, number well over 7,000 worldwide. There are 1,200 in North America, 900 in Europe, and 640 in Australia. They represent a vast group occupying niches in both still and running water. Their greatest diversity is found in and around running water. Distinguishing the species of adult or larva is very difficult and usually impractical when waterside. This situation is not lost on an angler who will find several species present in significant numbers on any given body of water. Fortunately it is relatively easy to identify a caddisfly as belonging to one of five groups: Net-Spinners, Free-Living Caddis, Tube-Case Caddis, Saddle-Case Caddis, and Purse-Case Caddis. By briefly studying these groups we can later apply fishing strategies to match them." Above are images of a sedge adult and a green sedge larva. Caddis larva are tough to seine net, they hold firm to their homes and are easiest captured by flipping rocks.

Lets not forget those insects that go through an Incomplete Metamorphosis (meaning their life cycle has only 3 stages: egg, nymph and adult (dun [subimago] and spinner [imago]) - they don't create a Chrysalis in which to Pupate)

Mayfly (Insects of the order Ephemeroptera are commonly known as Upwinged Flies or Mayflies. We primarily found Blue Winged Olives, a type of Baetis and March Browns or Rhithrogena Morrisoni)

"After hatching, the nymphs feed on algae, plant debris, and other small food particles carried in the current. They grow through several instars before reaching maturity. This takes from a few months to a couple of years, once again depending on species and prevailing conditions, and also time of year when the eggs were laid." Above is a an adult BWO Dun, a mature BWO nymph with developed wing pads indicating its ready to hatch, a BWO husk (it hatched soon after we captured it in its nymph form) and finally a March Brown Nymph.

Stonefly (members of the insect order Plecoptera. We primarily found Skwalas and Winter Stoneflies.)

"The presence of stoneflies in a river or stream has always been a good indicator of a healthy aquatic environment. These members of the insect order Plecoptera are found in cool, well oxygenated flowing waters and occasionally along the wave-swept shoals of northern latitude lakes. Stoneflies have a worldwide distribution and thus are an important fish food source in both the larval (nymphal) and adult stages. Their life cycle which can include as many as 3 years in the larval stage is a significant reason why they are of such interest to fish. The larvae are benthic dwellers, crawling amongst the rock and rubble of the faster moving parts of the stream known as the riffle and run zones. Depending on the species, stonefly larvae can be herbivorous, omnivorous or carnivorous. Smaller aquatic invertebrates such as mayfly nymphs, dipteran larvae, algae and detritus are all common food sources of stonefly larvae." Above are images of stones caught in our seine net, a Skwala nymph, an adult Winter Stonefly and an adult Skwala Stonefly. Find, shallow oxygenated water to find these nymphs, they're great clingers but poor swimmers.

Some other items on the trout menu which we found include a couple of species of annelids (segmented aquatic worms) including this good sized leech which ended up eating the aquatic worm to the right.