Midges, baseball fans recall, are the gnat-like insects that rose from Lake Erie last October and descended upon Chamberlain in the bottom of the eighth inning of a playoff game against the Cleveland Indians, distracting him into throwing two wild pitches. Cleveland scored the tying run without a hit. The Yankees eventually lost the game and eventually the series.
During mating season, the air at Lake Myvatn can also be thick with male midges, each hovering, waiting for a female to join him. "It's a like a fog, a brown dense fog that just rises around the lake," said Anthony R. Ives, a professor of zoology at the University of Wisconsin.
Yet at the same time in other years, hardly a midge was to be seen at the lake. This boom-and-bust cycle -- the density of midges can rise or fall by a factor of a million within a few years -- drew the interest of ecologists like Dr. Ives.
Time to peek out from lurking.
Midges of family Chironomidae (Diptera) are quite a fascinating group of insects that can be found on every continent with a couple thousand species identified to date. The "boom and bust" cycles have been noted in many places worldwide and the nuisance/cleanup problems they cause can cost even small cities millions of dollars annually.
While the midges of Lake Myvatn show a strong reliance on diatoms, other midge species will target other phyotoplankton taxa, such as Chlorophyta and Cyanobacteria.
As the Nature article mentions, sediment structure is critical for larval development and each species will have its own requirements. Some in softer, organic sediments, others in firm mineral sediments, while others will bore into plant tissue. There are also a considerable number of biotic and abiotic environmental conditions that can influence populations, such as water temperature or nutrient loading.
For some blatant self-promotion, I've previously modeled a nusiance chironomid in central Florida:
Lobinske, R. J., J. L. Stimac, and A. Ali. 2004. A spatially explicit model for immature distributions of Glyptotendipes paripes (Diptera: Chironomidae) in central Florida lakes. Hydrobiologia 519: 19-27.
There's a lot more that we know, but I'll cut off now to avoid boring everybody.
You are definitely not boring me. I'm always looking for some real examples of boom and bust cycles. Do share more!
Since you asked.
In the large, shallow central Florida lakes I studied (average max depth about 3-5 meters), water level (determined by local rainfall) was one of the determining factors. Because the midge larvae of the species I studied specific about sediments, they were also sensitive to water depth, so that their colonization zone would shift with changing water level. Lower water levels also tended to concentrate nutrients in these eutrophic systems, leading to algae blooms that provided abundant food for the larvae and large populations. Locally high densities of 40,000 - 50,000 per square meter and lakewide means of 2,000-3,000 per square meter could be encountered. New Jersey light traps along the shoreline during these times could have their 1 pint sample jars filled overnight. When water levels rose, the nutrients would be diluted and algal concentration drop, reducing the midge populations. Trends also shifted with temperatures and the overall nutrient loading in the lake.
I'm interested in the light traps that you used to collect the insects. Is it possible to make a homemade trap? And if so, could you describe what it looks like? I wonder if it would work to catch the "fish flies" that are common in my area. I'm thinking that something along these lines would make for a great project for my students.
Thanks for the details of how abiotic factors influence the midge populations!
I'd be interested in what Richard says.
I've used light traps in the African Rain forest ... OMG you would not believe what flies into them. (mostly ants it turns out, but lots of other stuff).
What's a "fish fly"? Is that like a "lake fly"?