DEER FLIES

      When I walk in deciduous, bottomland woods in southeastern Pennsylvania during June, I am pestered by several female deer flies.  At least a few of them always succeed in biting me; and those bites hurt!

     Broad-headed, with brightly-colored, large eyes, female deer flies are almost a half inch-long, have clear wings with dark bands and yellow-brown and dark-striped thoraxes and abdomens.  

     Deer flies live near waterways and standing water in wooded bottomlands.  There on warm, sunny days, male deer flies sip flower nectar and ingest pollen, but females need a meal of blood from large mammals, including white-tailed deer and people, so they have enough protein to lays eggs.  

      Female deer flies locate their victims by sight, smell, body heat and the presence of carbon dioxide in the air.  When a large mammal is perceived, including me, each female deer fly silently circles her intended victim and finally lands on it, bites it and ingests a bit of its blood.  Victims try to avoid or discourage female deer flies from biting, but those insects are persistent and finally drink some blood!

     That mammal blood allows each female deer fly enough nutrition to develop hundreds of eggs she lays on vegetation hanging over shallow water or muck along the shores of waterways and impoundments.  Larval deer flies hatch on that foliage and drop into the shallows or mucky shoreline where they consume tiny invertebrates and other organic material, pupate and emerge as adult flies by late May.  By early June, female deer flies are watching for mammals to bite and partake of their blood.

     However, many unlucky deer flies are eaten by flycatching birds, bats, dragonflies, hornets, spiders, frogs and other kinds of  insect eaters.  Obviously, deer flies are part of several food chains.

     Female deer flies are interesting little denizens of bottomland woods, but they are a pest with their painful bites.  They readily seek out large mammals to get at least one meal of blood.          

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