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March Flies

Some Spiders Still Active

10-29-18 march fly and spider_U1A1162Spiders are ectotherms – warmed and cooled by their environment. In the fall, those outdoor species that remain alive through the winter begin preparing themselves by producing antifreeze proteins that allow their tissues to experience below-freezing temperatures. When a small particle of ice first starts to form, the antifreeze proteins bind to it and prevent the water around it from freezing, thus preventing the growth of an ice crystal. Some species survive in temperatures as low as -5 degrees Celsius.

The pictured hammock spider, still active in late October, is nourishing itself by drinking the dissolved innards of a fall-flying March fly, whose name comes from the predominantly springtime flight period of most March Flies (of the 32 species in the genus Bibio in North America, only three fly in fall).

A common belief is that once cold weather appears, outdoor spiders seek shelter inside houses.  In fact, only about 5% of the spiders you find in your house lived outside before coming into your house, according to Seattle’s Burk Museum.  The reason people tend to notice them more inside may be because sexually mature male spiders become more active in the fall, wandering far and wide in search of mates.

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March Flies Emerging

5-30-18 march fly_U1A4814If you’ve been spending time in fields and meadows recently you may have been witness to the mass emergence of a species of fly known as the March Fly (Bibio albipennis). Their common name is a misnomer, for they are usually seen in April and May in the Northeast. The hatching of March Fly eggs in the soil produces larvae that feed mostly on decaying organic matter. After the larvae pupate and emerge as adults, you find dozens of flies clinging to grass and other vegetation.

Another species of fly in the same genus is known as “Lovebugs,” due to the habit of the males remaining “plugged into” the females during long copulations. Entomologist Stephen Marshall has this to say about their presence in southeastern U.S.: Even though adult Bibionidae are innocuous non-biting insects, the sheer number of fornicating flies fouling car windshields, pitting paint jobs and clogging up radiators renders Lovebugs a well-known Bible Belt nuisance.

The male and female March Fly are sexually dimorphic, differing in appearance. Like many other flies that form male swarms, the males have large heads with massive eyes. The females’ eyes are much smaller. Both are common on flowers and can be significant pollinators of fruit trees.

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Lovebugs Mating

11-18-16-lovebugs-mh_20091020_004606_2If you see a swarm of small black insects bobbing up and down in the air, you may well be observing the mating ritual of March Flies, also known as Lovebugs. These flies belong to the family Bibionidae, and the majority of species emerge in the spring, hence their common name. (In the Northeast, many appear in April and May.) However, there are certain species which emerge and mate in the fall and they are active now.

March Flies are dimorphic. Males (fly to the left in photo) are easily discernible because of their large eyes, essential for finding mates and chasing competing males. Males comprise most of a swarm, performing an aerial ballet as they bounce up and down, courting females as they emerge from the ground en masse. Once mating has taken place, the male and female of certain species remain attached to one another, even in flight. This is where the name “Lovebug” came from.

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