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Let’s Talk Bugs
by Tom Lager
Within the last weeks I explored the Pine River below Wild Rose, looking for promising trout habitat. To me a good indicator is the macro-invertebrate community. As I walked up to the river, I could smell the skunk cabbage I had walked through. The pungent odor hung in the air – a still and very warm afternoon. As those of you who are familiar with walking the stream beds of this watershed know, sand is a common stream bottom substrate. A sand bottom is unstable and in most areas is constantly drifting downstream, exposing rock or bole wood and then eventually covering them again. Periodic spates flush and scour the channel, essentially sandblasting the aquatic insect community.
I did my usual thing – pulling and lifting rocks and logs to see who was there. Down stream of the K Bridge, I found good examples of the filter feeding community. The most common critters were the net-spinning Hydropsychid caddisfly larvae and Brachycentrus larvae. Both of these insects are filter feeders. The nets of the Hydropsychid larvae were easily visible (see the nets in the lower right corner of the picture below, along with small larva), attached to rough surface features and nearby debris anchored to the log surface. The larvae secrete silk from glands located in the head and weave back and forth forming a mesh net. Research has demonstrated certain species construct specific mesh sizes, presumably to capture food items of a preferred size. The Brachycentrus filter via spines and hairs on front legs, which are held-up in front of their square rectangular long cases to strain the current.
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I think you can imagine why filter feeders are the dominant organism within this community. It is largely because logs, twigs and rocks provide the most stable substrate for insect colonization. The sandy bottom is too unstable and too mobile for insects to live on or grasses, watercress and other plants to grow in — at least during the spring. (Artificial siltation takes this to the extreme and can smother a whole stream).
There are other organisms present as well, but in lower numbers and diversity. Some examples of these are mayfly larvae which feed by scraping the algae and by gathering debris / food items from the rocks and logs. Two examples are visible in the upper mid-area of the figure; an Ephemerellid (Sulfur) and Baetid (Blue Winged Olive) larva. The three cone shaped structures (middle of figure) are pupae cases of black fly larvae (also filer-feeders in the larvae stage).
I must admit, I did see several other non-bug items about the holes and pools that will cause me to return to this stream with elk-wing caddis patterns in hand. The evening sun by this time was awesome as I watched the low angled rays break through leafless trees and flame outlines of midges still on the wing. Wow — what a place He has made. The meanders of the Pine slowly continued downstream – I turned upstream to my car. Skunk cabbage, turned rocks, lots of great bugs, a few trout – a time well spent.
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