Recently, Bug of the Week paid a visit to the family-oriented burying beetles in “They eat dead things, Part I”. This week we meet the real masters in the art of eating dead things, the blow flies also known as bottle flies. Blow flies are regular residents in our landscapes and forests where they cruise about ever vigilant for rich organic resources such as carrion. While living animals are of little interest, cadavers release wonderful, aromas irresistible to blow flies. Their strategy in life is to rapidly locate recently deceased animals, lay eggs before the arrival of competitors such as burying beetles, and monopolize the rich nutrients provided by decaying flesh. To see just how quickly blow flies could find a dead thing, I placed a piece of meat on my picnic table one sunny morning. The first blow fly appeared and began to slurp the tasty juices in less than four minutes. If a carcass is suitable, the female blow fly will deposit a few score to more than 100 eggs on the flesh. Wounds and orifices usually to first places eggs are laid. Eggs hatch within a day into tiny larvae called maggots. Their sole purpose in life is to eat the liquefied decaying flesh and avoid being eaten by predators such as the American carrion beetle, Necrophila americana. Maggots molt two times before leaving the carcass to pupate in the soil nearby. After several days, new adult flies emerge to mate, feed on nectar and other liquid foods, and search for more dead things. While the image of a carcass writhing with a mass of maggots may be repulsive, imagine what a vile and smelly place the world would be without Mother Nature’s sanitary force of blow flies and burying beetles. They are the heroes of recycling. Blow flies serve several other useful purposes as well. 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. By placing aseptic maggots of the blow fly Phaenicia sericata in infected, necrotic tissues, doctors have successfully used maggot therapy to treat serious illnesses ranging from gangrene to osteomyelitis. Some species of blow flies such as the screwworm, Cochliomyia macellaria, infest wounds of livestock and may be important pests. For those of us addicted to the recent genre of forensic dramas on television such as Bones and CSI, Phaenicia sericata and Phormia regina are household names. For many years forensic entomologists have cataloged the seasonal activity, behavior, and habitat patterns of several species of Calliphoridae. The relationships between temperature and development are well known for many species of blow flies and their carrion-consuming relatives. By collecting fly larvae from the body of a crime victim, identifying the species and developmental stage of the fly, and correlating these facts with local weather information, detectives can accurately estimate the post-mortem interval and determine when a body was placed at a crime scene. This information has been used to convict perpetrators of numerous homicides. While testimony of humans can be sketchy, prosecutors know that flies tell no lies. Now that we have extolled the virtues of the blow fly, we would be remiss if we failed to point out one small issue associated with some questionable eating habits of these marvelous flies. Although a feast of decaying flesh is superb, blow flies like other liquid and semi-liquid cuisine such as doggie droppings and excrement from most other creatures. They feed by slurping nutrient laden liquid with sucking-sponging mouthparts. Unfortunately, part of the eating process of a blow fly also involves the regurgitation of liquid from its former meal along with saliva to aid in the digestion of its next supper. As you enjoy your steak or chicken at the next picnic, consider where the blow fly might have dined just before it visited your plate. I always recall the lyrics of the old song “shoo fly, don’t bother me” and conduct my shooing with extreme prejudice.
We thank our gruesome friends Amy Ludwig and Ian Scheibel for providing the inspiration for this Bug of the Week. Information for this episode came from Herm’s Medical Entomology by James and Harwood, Macmillan Press and from the web sites listed below.