by Joe Shorthouse, Professor Emeritus at Laurentian University and summer resident of Manitoulin Island
ASSIGINACK—Islanders who visited the Angry Antler’s vineyard near High Falls earlier this fall, owned by Richard Krasowski and his wife Louise Serré, were rewarded with an amazing experience as they walked along rows of grape-laden vines. Not only were visitors impressed by the quantity of the juicy grapes, many decided to pick a box for making jelly, juice, or wine once back home.
My wife Marilyn and I enjoyed the two hours we spent walking the rows and picking grapes, but as an entomologist, I was fascinated by clouds of insects called midges flying above select parts of the vineyard. These midges were not in the vineyard to enjoy the grapes, but rather they were there to engage in a special type of reproductive dance or ritual called swarming which can be explained as a vast singles party for flies seeking mates.
Swarms of midges often contain millions of rapidly flying flies and they often accumulate at the heights of people throughout the Island from spring to fall. Often mistaken for mosquitoes, the adults of midges are harmless and the appearance of swarms is only temporary. Swarms found at the vineyard likely occur for only a few hours when the light and temperatures are just right in the fall.
Midges are small, delicate mosquito-sized flies with long legs and slender wings. Males have large bushy antennae and are often referred to as “fussy bills.” They are of the insect family Chiromonidae and are commonly referred to as chironomid midges or ‘gnats.’ There are about are about 750 species in Canada. Unlike their mosquito relatives, adult midges do not have mouthparts, don’t feed, and therefore cannot bite people.
Midges are aquatic insects in the larval stage tolerant of a wide range of environmental conditions including slow moving streams, stagnant ditches, and ponds and lakes rich in decomposing organic matter. Larvae of most species of midges are highly desirable organisms in aquatic habitats where they are an important source of food for fish. Larvae ‘clean’ the aquatic environment by consuming and recycling organic debris. Adult midges are important sources of food for many species of birds.
There are four stages in the life cycle of midges: eggs, larvae, pupae and adults. Eggs are laid on the surface of water then sink to the bottom and hatch within a week. Larvae of some species live on the surface of rocks at the bottom of lakes, while others burrow into the mud and construct small tubes in which they live. Organic matter suspended in the water is used as food for the developing larvae.
The larvae of some species turn pink and then a dark red giving them the name “blood worms” because of haemoglobin in their blood that allows the larvae to respire in areas of low oxygen.
The larval stage last from two to seven weeks depending on water temperature. They transform into pupae while still in their tubes, then after three to four days, the pupae swim to the surface and the adults emerge several hours later.
The entire life cycle in the summer from egg to adult can be completed in two to three weeks. However, in the fall, the larvae do not pupate and instead suspend their development and pass the winter as mature larvae. Pupation and emergence of adults occurs the following spring in early May. Several more generations of midges are produced throughout the summer resulting in mass emergence of adults.
Swarms of midges commonly appear on the Island in the early spring and can be annoying as you walk or ride bikes down roads, especially with your mouth open. Swarms are sometimes so thick they look like plumes of smoke from afar. Adults live for four to seven days so the mating dance is understandably frantic as all their energy is spent looking for mates rather than eating.
While the masses of midges may look like an unruly, enveloping gaggle, the clouds are actually organized mating dances where females come to find a mate. Most individuals in the giant mating swarms are males. Females come looking for these swarms and fly into the mass. Somehow, throughout all the chaos, the females select a male for mating.
Mating occurs while they are flying in the mass and the actual sex act, which occurs while they are flying, lasts only a second or two. The females then fly back to aquatic areas to lay their eggs while both males that have successfully mated, and the majority who have not, drop dead soon after.
Midges that appear in the fall, such as those found for a few hours on warm days, tend to congregate over markers such as stones in fields. In other words, both male and female midges are programmed to search for light-coloured stones about the size of dinner plates found in pastures. Those found at the Angry Antlers mistook the tops of wooden fence posts for stones and readily accepted them for their dances. The posts are used to support the vines and it was amusing to see columns of “smoke” along the rows of grape vines.
To my amusement, some of the swarms we saw that day were attracted to the rounded top of the hood of my wife Marilyn’s jacket. To the midges, the top of her head looked like a stone in a pasture making it an ideal place to swarm and mate.
However, to Marilyn’s chagrin, the mass of highly agitated midges followed her as she walked down the rows of grapes. When asked what she should do, the only answer I could give was ‘Don’t look up and keep your mouth closed!’
Midges often swarm on people who are the tallest objects in flat landscapes making us sort-of lightening posts for insect mating. However, when you come across swarming midges and they decide to use the top of your head as a marker, try to get down low and blend into the background. I am taller than most people, so when in a crowd of people and midges begin swarming above our heads, I pretend to tie my shoe and the insects move to someone else!