There are more than the usual number of these hefty flies inside her cottage this fall, too, and she suspects there’s a connection between their persistence and the woodchuck that shuffled off its mortal coil under her floorboards in October (on the bright side, now she can fill the hole under the house without worrying about killing the woodchuck). 

What’s a Blow fly?  Blow flies and bottle flies are members of the family Calliphoridae.  Their lifestyles can be off-putting (hint – they’re sometimes called “filth flies”) (the BugLady acknowledges that there may be a certain “ick” factor here).  Females probably use chemical and visual signals to locate the flesh, carrion, wounds, orifices, and/or mammal poop on which they oviposit; the eggs hatch quickly and the larvae (maggots) feed on/in their often-odiferous milieu.  The maggots have to compete for food with the larvae of other insect species, and they must dodge the jaws of carrion beetles, spiders, birds, and frogs.  They pupate in the ground.   

The name “Blow fly” comes from the days of Shakespeare, when a piece of meat occupied by maggots was said to be “fly blown.”

Adult flies often feed on nectar.  Some species of plants (like Pawpaws) have developed especially stinky flowers in order to attract them, and according to The Missouri Department of Conservation website’s Blow fly page, they’re attracted to “some tropical arum species you may see at a botanical garden, and cactuslike stapelia houseplants from South Africa, whose flowers look like giant open sores.” Yes, pictures are available online.

Blow flies have – literally – medical applications, both historically and in the present day.  Says Michael J. Raupp, Extension Entomologist at the University of Maryland, in his Bug of the Week blog (the original Bug of the Week!), “During the American Civil War, surgeons noticed that blow flies often infested the grievous wounds of soldiers. Physicians were surprised to see wounds of maggot-ridden soldiers healing more rapidly and with fewer complications than injuries of soldiers without maggots. Many blow fly larvae consume dead and dying tissues rather than healthy ones. Furthermore, they secrete potent chemicals that kill harmful bacteria and aid in the healing process. Using blow fly larvae to treat wounds is called maggot therapy.” 

And, as CSI fans know – forensic entomologists have charted down to the minute all the permutations in the chronologies of some blow fly species in order to estimate how long a dead body has been dead.  

Though they can spread some nasty germs (if those germs are present, which they often are not), they don’t bite, and they are vital members of Nature’s clean-up crew.  Raupp calls them “heroes of recycling.” 

BLUE BLOW FLIES (Calliohora vicina) (“calliphora” means “bearer of beauty”) can be seen in cool, shady habitats around the globe, primarily in the Northern Hemisphere, but they’re also found in scattered locations in the Southern Hemisphere.  They’ve been recorded in South Africa and uncommonly in Australia, where they’re called European blow flies.  Wikipedia says that they probably travel by the world by airplane.

Females lay eggs – as many as 300 – on a suitable substrate, and if the humidity is high enough they hatch quickly, but they crawl away to find drier conditions when it’s time to pupate.  The larval stage lasts about three days, depending on temperature, and the entire life cycle is about 20 days, most of it spent as a pupa. 

Sources say that adult Blue blow flies are considered “efficient pollinators,” especially of crops like carrots.

Despite the cold, there are still bugs out on our landscapes (and inside, too – the BugLady recently photographed a Bridge spider in her storage unit, and she found an earwig on her sink, but she’s pretty sure that it, like the tree frog that was in the shower, came in when she brought the geraniums inside for the winter).

Kate Redmond, The BugLady

Bug of the Week archives:
http://uwm.edu/field-station/category/bug-of-the-week/