Often the Master Gardener clinic receives samples of fly maggots from clients. The most common scenario that the customer describes is “maggots are crawling out of my carpet!” Sometimes maggots appear by the dozen or up to hundreds over time. Usually the client is disturbed by this, which is understandable. Maggots have a talent for repulsing everyone.
Identification: Of the maggots that we find in peoples’ houses, calliphorid maggots are the most common. Calliphorids are also known as blow flies or bottle flies. Maggots are the larval stage of the flies. Fully grown maggots can reach over a half inch in length. Mature blow fly maggots are creamy in color. Maggots have a very typical body shape; the head end is slender and tapers to a point while the rear end is thicker and ends bluntly. The hook-like mouth parts are the only visible part of the head of these flies. The rear end of the maggot has two kidney bean shaped patterns on the end; these are spiracles used for breathing. Spiracles are used to identify the family and species of fly maggots since, superficially, they all look the same. Mature maggots will pupate. The pupa is concealed in a red-brick case called a puparium. These are smaller than the maggot and more circular in shape. Adult blowflies resemble house flies in shape but are often metallic green or blue in color.
Lifecycle: Adult blow flies lay eggs on or near rotting vegetation, manure or animals. Eggs hatch very quickly, and maggots begin to consume the decaying food. Maggots pupate and emerge as adults within a few days, depending on the temperature. Total developmental time from egg to adult can happen as quickly as a week, given good conditions, and depending on the species. They develop and consume food quickly, so much so that when a maggot has matured, it moves away from the food source to digest and prepare for pupation. During this movement away from the food, a maggot can travel quite far, up to 100 yards. This is when people most often discover the maggots as they disperse through a wall and across the living room floor.
Management: Using insecticides is unnecessary when managing blow fly maggots in the house. In fact, insecticides may cause secondary pest problems, such as carpet beetles, by leaving behind the dead insects. Vacuum up the maggots as you find them on the floor. I prefer an industrial vacuum for this type of job. Be sure to also look under rugs and other obstacles on the floor. Maggots will seek protective places to pupate and turn into flies.
There is good evidence to assume that something has expired near by or rotting trash is left unattended if maggots are found migrating within a house. If maggots are found by the hundreds over a period of time, you can expect that the dead animal is large, such as a cat, possum or raccoon. Logically, if very few maggots are found, you can expect a small animal, such as a bird or mouse has died. Either way, it is important to find the dead animal, or unattended trash, and have it removed. Dead animals and trash can attract many other household pests, such as carpet beetles. Maggots generally move in a straight direction away from the food source during this post feeding stage. Investigate in the direction that the maggots are coming from. Keep in mind that maggots can travel quite a distance from their food source so don’t be discouraged if you do not find the source. If maggots appear to be coming from the wall boards, look outside the house along the foundation for any dead animals or more maggots. It is also worth checking up in the attic; the maggots could be migrating down, inside the walls from the attic or roof eaves. Be sure to wear gloves when handling the dead animal to avoid disease.
Blow flies are very important insects. They are usually the first critter to begin the process of decomposition and the recycling of trash, dead animals, and of course humans. A maggot mass can reduce the body weight of a corpse by 50% in a matter of a couple of weeks. There are many species of blow flies, and their lifecycles and habits are diverse. Each blow fly prefers certain seasons to be active and certain habitats. For example, in the cooler months like in fall and winter, species such as Calliphora vomitoria (nice name, huh?) are most commonly found on carrion, while Phaenicia sericata is commonly found out in the hot August days. Some flies even prefer shade over sun. Since blow flies are very specific in development and habitats, and they are the first insects to a corpse, they have proven to be the best crime investigators. A whole field of study has evolved from blow fly biology, called forensic entomology. Experts in this field use the fly maggot’s identity, habitat preference, and developmental rate to determine the moment that someone was murdered and ultimately solve crimes. So, the next time you run across a filthy maggot, I hope you appreciate their important social services as janitors, morticians and crime solvers before you suck them up with your vacuum!
For more information about flies in the house, see WSU PLS-31 “Blow flies, cluster flies and screw-worm flies” http://www.puyallup.wsu.edu/plantclinic/resources/pdf/pls31blowflies.pdf
For more information about forensic entomology, visit: http://www.missouri.edu/~agwww/entomology/
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