Blow Flies

Facts & General Information

What Are They?
Also known as bottle flies, blow flies are filth loving flies. They breed in animal carcasses or fresh wounds.

Why Are They in Your Home?
Many times people find blowflies in the home. This often happens when the flies discover a dead squirrel, mouse, or bird that the homeowner had not seen.

Identification / Appearance

What Do They Look Like?

blue bottle fly
green bottle fly

Color
Adult blow flies vary in colour, ranging from metallic green, blue, bronze to black with hints of copper.

Size
They are slightly larger than house flies, measuring about 6 to 16 mm long.

Their larvae are known as maggots; they have smooth, legless, worm-like bodies and are white to yellow in colour. Pupae have reddish-brown shells.

Body
The pests have hairy backs and are strong fliers.

Habitat

Where Do They Live?
Around homes, the garbage cans are also favorite blowfly breeding sites. The flies will also deposit their eggs in animal droppings. Some blowflies will enter homes. If meat or other food it exposed, the flies will even deposit their eggs in it.

Life Cycle & Reproduction

blow fly life cycle
Image credit: https://www.nlm.nih.gov/

Eggs
Adult females are able to lay up to 500 eggs in clusters of 20 or more. They reproduce on dead decaying animals, open wounds in live animals, or exposed meat. Blow fly eggs develop into full-grown larvae within several days, and then enter the pupal stage for anywhere from one to three weeks.

Read more about blow fly maggots.

Blowflies prefer to deposit their eggs on the carcasses of dead animals. Sometimes the flies find a dead squirrel, mouse, or bird around a home. The flies will search out the animal in the attic, the chimney, or the rain gutters.

Many times the flies make their discovery before the homeowners do. For many homeowners, the flies are the first clues that an animal was even nearby.

If there is not an animal available, the blowflies will readily deposit their eggs in garbage cans. Scientists have reported finding thousands of blowfly larvae in one garbage can.

Larvae

Blowfly larvae grow and develop into adult flies. Many people call them maggots. The female flies deposit their eggs on decaying material. When the eggs hatch, the blowfly larvae eat the decaying material.

Each time the larvae molt, they grow larger. After the last molt, the larvae can be almost one inch long. They are whitish in color. They have no eyes and no legs, so blowfly larvae do not travel far.

As they grow larger, the larvae burrow deeper into the material where they are feeding. The larvae can finish developing in two weeks. However, some species take more than a month for the larva stage. Unfavorable temperature can make the larva stage last even longer.

Adults
When they are fully grown, the larvae move out of the food material and burrow down into the soil. The larvae are ready to change into adults. In the summer, the change into adults takes 3 days to two weeks, depending on the species. In the fall, the larvae burrow into the soil and wait until spring to change to adult blowflies.

Problems Caused by Blow Flies

Infestations often indicate and add to the unpleasantness of sewer issues in homes or decaying dead animal or garbage. People who live on or near farms may have more issues with blow flies, as they are attracted to animals or manure.

Signs of Infestation

If homeowners find one or two blow flies, or blue bottle flies, in the house, it is probably a sign of an outdoor infestation. It can mean that a door was left open or that a screen is torn.

If homeowners start to see a lot of blow flies in the house, it may be a sign that something is wrong. Very often the flies are a sign of a dead mouse or bird in the attic.

Any injured or dying wildlife that wanders onto the property can attract blow flies. Family pets with an illness or buried in the yard may entice the pests as well. Be sure to follow guidelines for burying animals properly to avoid attracting blow flies and other scavengers.

In any case, the pests’ presence typically points to some kind of larger, sanitation problem.

How to Get Rid of Them

Homeowners who find blowfly larvae should eliminate the material that they are eating.

The first, and most important thing to do is find the fly breeding site. There will usually be a large number of flies buzzing around the site. If things are quiet, the buzzing sound may lead to the site.

If there is a dead mouse or bird, homeowners should not try to remove it barehanded. A trash bag can be placed over the carcass and used to grasp it. Invert the bag over the carcass so it ends up inside the bag. Place a second bag over the first.

After removing a carcass, it is sometimes necessary to apply an aerosol insecticide for fleas, bat bugs, beetles, or insect scavengers. Depending on the location, a dust insecticide may be easier to apply and be more effective than an aerosol.

Ineffectiveness of Spraying Adults
People who try to eliminate blowfly larvae by spraying the adult flies are usually disappointed with the results because the flies do not go away.

Get Rid of Larvae with Vacuum
The larvae can be removed with a vacuum cleaner. They can also be killed with an aerosol insecticide. Adult flies can also be vacuumed from windows indoors.

Sometimes homeowners must call on a pest control professional for help in finding the source of the larvae, especially if it is in a hidden location like the attic or inside of a wall.