By Dr. David Wartinbee, for the Redoubt Reporter
As we motored up river after a great day of rainbow fishing on the Kenai River, we couldn’t help but smile as the setting sun retreated below a golden western sky.
Smiling was short-lived, however, because we were being peppered by hundreds of tiny bugs flying just above the river’s surface. We kept thinking of the joke about how happy motorcycle riders end up with bugs on their teeth. Thank goodness for my glasses and learning to keep my mouth shut.
What was going on here, and what were these bugs that were stinging our faces?
A few days earlier while working in the yard, I was surrounded by a swarm of tiny bugs that were doing their best to drive me crazy. They seemed content to buzz around my glasses and crawl on my beard. What were these bugs and what were they doing?
The bugs in both situations were the same, but were involved in two different goals as adult aquatic insects. First, both situations involved an encounter with black fly adults. Black flies are tiny “true flies” and members of the family Simuliidae. Those hitting our faces as we headed home at dusk were probably laying their eggs on the surface of the water. Those swarming around my head were sizing me up and preparing for their next blood meal.
For some reason, Alaskans often call them whitesox. In some areas of the country they are called buffalo gnats because they have a disproportionately large, humped thorax for such a small insect. The “black” refers to their predominant color. No matter what we call them, these tiny insects can be distracting.
We are not the only area where black flies are found. In fact, they are particularly common in most areas that have flowing waters, because their larvae are only found in streams and rivers. I am sure we have all heard stories about swarms of black flies ruining a particular fishing or camping trip somewhere in Alaska or Canada, but they can be found all over the world.
My worst experience with black flies occurred while collecting bugs from a stream in a Venezualan rain forest while wearing shorts and a T-shirt. I couldn’t count all the bites I received that day.
Even if your favorite pastime doesn’t involve playing in streams, black flies are more than willing to come to where you are. Some adults are known to travel up to 50 miles to find a blood meal. The adults live for up to 60 days, which is a very long time for many insect adults.
Their longevity enables them to be patient and to wait until they find a juicy, exposed part of your body. Then they strike. By the way, they will happily take their blood meal from your dog, if given the opportunity.
The biting black fly adult releases an anti-coagulant into the wound so the blood will flow freely. On all too many occasions we don’t even know that we’ve been bitten until we see a place on the skin that is bleeding. Those of us who are allergic to the anti-coagulant saliva may then develop a large, itchy welt on the surface of the skin.
As if this weren’t enough for one critter, adult black flies are able to produce multiple batches of eggs. The number of eggs produced by a female reflects her success in finding one or more blood meals. Eggs are usually deposited on the surface of a stream or river close to dusk, which explains why we encountered so many while boating at the end of the day. The larvae may hatch out immediately, although some species delay hatching for several months.
Growing larvae have a set of very specialized labral fans on their head that look like a minute fishing net. They hold the fans out in the current and filter out fine leaf particles, algae and even bacteria. When food particles are caught, they collapse the fan, feed on the material and then return to their miniscule version of dipnetting for lunch.
Once the larva has grown to a particular size, it forms a pupa and transforms from an aquatic insect into the flying adult. The pupa is often attached to a submerged rock, and in a couple days the adult is ready to go. It then forms a gas bubble around itself, pops out and rides that bubble to the surface so it can fly away.
We have several different species of black flies in Alaska, and each seems to have its favorite emergence time. Additionally, many black flies are able to complete multiple life cycles in a summer. Perhaps now we can understand why they are so abundant.
In some parts of the world these pesky flies carry serious diseases. In many parts of Africa, black fly adults transmit a very small nematode worm that enters the wound site. In turn, the worm causes “river blindness.” This parasitic worm is a major cause of blindness in tropical areas of the world.
Fortunately, there are no known human diseases carried by black flies in Alaska. However, even without being a vector for some disease, black flies can be a bloody pain in wherever they bite you.
David Wartinbee, Ph.D, J.D., is a biology professor at Kenai Peninsula College’s Kenai River Campus. He is writing a series of columns on the ecology of the Kenai River and Cook Inlet watershed.