Tuesday, December 6, 2016

Green Bottle Flies

Bottle fly on the deck  - REK
I saw this green bottle fly on our deck last summer, not where I would usually expect to see it.  It is more commonly found on dead animals, sometimes swarming in an egg laying frenzy.  It is one of many species in the Calliphoridae family, known as blow flies, a term dating back to Shakespeare.  While not exactly warm and fuzzy insects, they play an important role in nature.

A few hours after laying out a dead rat - REK
They will arrive rapidly, usually the first insect to find a corpse.  Their association with dead animals is linked to anautogeny, the requirement of the female to feed on a particular meal before her eggs will become fertile, much as the female mosquito that feeds on us.  In the case of the blowfly, she gets the protein load needed to produce viable eggs and will begin laying eggs within two days.  This is convenient one-stop shopping as she then is able to place the eggs directly on the carcass that will feed her young larvae.
L. sericata on a dead wood rat - note larva behind wing-  REK
After emerging from the egg in 8 to 24 hours, the larvae will go through 3 instars in a predictable fashion.   The speed of growth and instar progression is temperature dependent.  As the maggot mass together, their salivary digestive enzymes break down tissue and the temperature in their vicinity can reach over 100⁰ F.   The predictable  progression of instars is a tool used by forensic entomologists to determine length of time a body has been dead.  In addition, in a closed crime scene, finding blow flies suggests that the body has been moved.

Life is not easy for a young maggot.  The competition for a dead body can be fierce.  When the larva isn't providing extra protein for scavengers such as vultures and coyotes, it is vulnerable to mites that are carried to the body by carrion beetles, thus eliminating competition to the beetles' larvae.  If it survives through the third instar, it will then crawl off into the soil to pupate.  I assume that if it is in a closed room with a tile floor it is out of luck.

Green Bottle Fly on a toothpick - REK
They have more than one role in nature.  Adults take nectar and have been used as pollinators of onions, cabbages, broccoli, kale, and also other Brassicaceae where they are more efficient that bees.  (Mothers, this is probably more science that you want to share with your children while getting them to eat their vegetables.)

L. sericata larvae  - Joseph Berger CC
Finally, the bottle fly larvae (medical maggots) were used in the Civil War to debride tissue from wounds and are still used occasionally today.  Since they only feed on dead tissue, medical maggots raised in a sterile environment can clean out inaccessible necrotic tissue, avoiding damage of opening a deep wound.  Their enzymes digest the dead tissue and stimulate granulation tissue for healing.

So what is not to love about Green Bottle Flies?  They return dead animals to the soil,  clean wounds and pollinate our vegetables.  Just forget what I said about kale.

More Green Bottle Fly details are here.