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Shadfly Story:
Shad Flies are also known as Mayflies, Dunes and Dayflies. They live from a few hours to 14 days. They are only found in freshwater habitats and are an important food source for fish, birds, bats and other insects. They belong to the family called Ephemeroptera, and there are 1500 different species throughout the world.
A pregnant female will fly over the water and dip her abdomen in the water, releasing up to 8,000 eggs, which sink to the bottom. The eggs then hatch into nymphs or naiads, which form a u-shaped burrow in the sediment at the bottom of the water body. They then feed on algae and bacteria in the lake bottom. They can stay there for a few months to a few years.
When the water reaches the right temperature, the nymph emerges, swims to the surface and sheds it skin. Then, the skin and wings harden and the nymph is known as a sub-imago, which flies to the shore. It then molts again, and is considered an adult. The males and females congregate over the water and mate, after which the male dies. The female then releases her eggs in the water and the cycle starts over again.
They are the oldest insect alive, and are believed to date back from about 300 million years ago. They have undeveloped mouth parts and cannot feed once leaving the water. They are the only insects known to molt while in subadulthood. It is a macroinvertabrate.
As the end of June nears, residents of North Bay on Lake Nipissing anticipate those lazy, hazy days of summer. With less eagerness, do they look forward to the annual onslaught of the notorious shadfly. The substrate of Lake Nipissing is the perfect habitat for the larvae of these harmless winged insects.
Each year as summer temperatures reach their peak, shadfly nymphs emerge from the lake in droves. Attracted to land by the light of the moon, the "shads" natural mating patterns are somewhat altered as the foiled shads dance in circles around city streetlights. After a warm summers night, residents will wake up to vehicles that have become an overnight resting post for these fine-winged insects.
The unmistakable sound of crunching shadflies signifies the beginning of summer as the insects are too numerous to dodge while going about business on city sidewalks. A leisurely bicycle ride on a warm evening during shadfly season becomes an exercise in breathing with one's mouth closed to avoid an unwanted insect meal. Roadways become hazardous as crawling masses of these night-flyers congregate underneath the brightest street lights forming a slippery film between tire and asphalt.
The end of the 2-3 week shadfly emergence is found to be the most obnoxious. Insects which have been swept into heaps by city shopkeepers foul the city air as peak summer temperatures speed up the decomposition process. The lakes appeal is lost to prospective swimmers looking for relief from the heat as they are faced with the stench of shadfly corpses littering the shore.
The saving grace of this winged storm is the lack of biting or sucking mouthparts. Unlike the itch inspiring mosquito and black-fly, the shadfly is only a menace to man because of its emergence in astronomical numbers.
So what purpose do these somewhat benign insects serve? For starters, the shadfly is an extremely important source of food for the walleye population of Lake Nipissing. In the years when a decline in the shadfly population is noticed, there is warranted concern for the health of the fishery in the following year.
The larvae of the shadfly live as a nymph or `naiad' in the substrate of ponds, lakes and streams. The genus Hexagenia, common to Lake Nipissing spends 2-3 years as a nymph. It is during this time that the shadfly feeds as the adults do not have functioning mouthparts. Therefore, all growth occurs in the nymph stage in preparation for an eventual emergence to mate. The shads usually emerge during the end of June when water temperatures near maximum. Shadflies are sexually dimorphous, meaning there is a male and a female sex. During flight, the female deposits her fertilized eggs as she drags her abdomen across the surface of the water. Molting occurs only once in the short 2-3 day life of the adult shadfly before re-entering the food chain as life-giving nutrition for other organisms.
For more information, read the Nugget articles.
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