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Durango Herald, July 12, 2007
Becky Gillette, Program Director
Caddis fly larva
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Tubes, kayaks, rafts and canoes are making their way
down area rivers in droves these days as sun-baked souls aboard seeking reprieve
from the scorching heat.
Though the river looks busy on the surface, most of us are not very familiar
with all the action happening down below.
Most aquatic insects, also known as benthic (bottom-dwelling) macro-invertebrates,
are the larval and nymph forms of flying fish food, including the mayfly, stonefly
and caddisfly. Any river or creek can be home to these diverse and interesting
creatures, and they’re easy to observe.
Find a spot 6-24 inches deep, where water flows moderately fast over rocks ranging
from grapefruit to watermelon size. You may have to wade out a few feet
for the best selection – wear shoes, face upstream, and watch your footing
on slippery, river-rounded cobbles.
With minimal disturbance to the river bottom, pick up a rock. Lift it out
of the water, flip it over, and quickly scan the bottom and sides looking for
movement. Visible critters range from a few millimeters to a few inches
long, with markings in shades of gray and brown.
For closer observation, use a plastic spoon to gently nudge any insects off the
rock into a small container filled with river water. Cool water is their
oxygen lifeline, so minimize the time in which critters might dry out or warm
up. To release them without harm, set your container in the river, then
tilt to empty it.
Caddisfly larvae and mayfly nymphs eat mostly algae and plants, and can spend
several years underwater. As winged adults, they live for days or maybe
weeks, surviving only on the biological drive to find a mate and lay eggs. Dragonflies
are predators in the river and also in the air, eating smaller insects and surviving
as adults for weeks or months.
Aquatic insects absorb dissolved oxygen using gills, which with close examination
(or a magnifying glass) are visible as feathery hairs on the bellies of some. Streamlined
bodies and feet with hooks help prevent being swept downstream.
Macro-invertebrate populations are monitored nationally as indicator species
for measuring water quality – their total immersion lifestyle makes them
good candidates. The caddis, stone, may, and dobsonflies, in particular,
are highly sensitive to contaminants and habitat degradation.
A century’s worth of mining waste in the Upper Animas watershed contaminates
run-off with heavy metals leached from acid soils, posing threats to macro-invertebrates
and fish. Despite this, the lower Animas continues to provide Gold Medal
fishing, and the caddisfly hatch a few weeks ago was pretty impressive as well.
For more information and beautiful illustrations to help you identify your insect
finds, try www.riverwatch.ab.ca (click
on How to Monitor) or www.boquetriver.org/adoptaqinvt.html.
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