If shiny green or blue flies suddenly show up in one room of your Cranford home, buzzing at the window or circling a light, they're probably blow flies. Unlike the odd house fly that slips in through a door, blow flies indoors usually point to one thing: something has died nearby, often a mouse, bird or squirrel inside a wall, ceiling or attic. The flies will keep coming until the source is gone. Below, we'll cover what blow flies are, how to tell what's drawing them and how to fix the problem. If you need help finding the source, our fly control team can track it down.
What Blow Flies Are
Blow flies are a family of flies that includes the green bottle fly and the blue bottle fly. They're a little larger than a house fly and have a shiny, metallic body in green, blue, bronze or copper. They're strong, noisy fliers, and they're attracted to light, which is why you'll often find them banging against windows.
Blow flies lay their eggs on dead animals, meat scraps, pet food and garbage. The eggs hatch into maggots that feed on that material for several days, then crawl away to a drier spot to pupate. New adults emerge and look for the nearest light, which is often the inside of your house.
What Blow Flies Indoors Usually Mean
A few blow flies near an outdoor trash can in summer are normal. Indoors, a sudden group of them is a warning sign. The most common causes are:
- A dead animal in the structure. Mice, rats, birds, squirrels and other animals sometimes die in wall voids, attics, crawl spaces or chimneys. Blow flies find the carcass quickly.
- Spoiled food or garbage. Meat scraps in a kitchen can, a forgotten package in the garage or pet food left out can all breed blow flies.
- Something outside close to a door or window. A dead animal under a deck or in a window well can send flies indoors.
Other clues that point to a dead animal include a bad odor that gets stronger over a few days, a stain on a ceiling or wall and maggots appearing on the floor or dropping from a light fixture.
Timing is another clue. Flies from a single dead animal often appear in a burst and then taper off once the carcass dries out or is gone. If a new wave shows up weeks later, there may be another animal, or an opening that keeps letting animals in. And don't assume the flies came from outside just because they're at the window. Blow flies emerging inside a wall head for the brightest light they can find, so the window where they gather is often a clue to which wall or ceiling to check first.
Blow Flies, House Flies And Cluster Flies
| Blow Fly | House Fly | Cluster Fly | |
|---|---|---|---|
| Look | Shiny metallic green, blue or copper | Gray with four dark stripes | Dull gray with golden hairs |
| When you see them | Sudden burst, often in one room | Steady numbers in warm months | Fall and on warm winter days |
| What it usually means | Dead animal or rotting meat nearby | Garbage or waste nearby | Flies overwintering in walls |
Are Blow Flies Harmful?
Blow flies don't bite or sting. The concern is where they've been. They breed on dead animals and garbage, then land on counters and food, so they can carry germs with them. Keep food covered and wipe down surfaces while you deal with the problem. A dead animal in a wall also brings odor and staining, and the animal that died may have gotten in through a gap that other animals can use too.
How To Get Rid Of Blow Flies
- Find the source. Follow the flies and the smell. Check the room where they gather, the attic above it, the basement below and any outside wall nearby.
- Remove it. Take out spoiled food or garbage right away. If an animal has died in a wall or ceiling, it may need to be removed through a small opening.
- Clean the area. Clean up fluids, maggots and debris, and deodorize the spot. Wear gloves and avoid touching a carcass with bare hands.
- Seal the entry point. Find out how the animal got in and close the gap, or the same thing can happen again.
- Clear the remaining flies. Once the source is gone, a vacuum or fly swatter takes care of the adults. They won't keep coming without something to breed in.
Outdoors, keep garbage in sealed bins and rinse them often. Our guide to trash can maggots has more on keeping bins clean.
When To Call A Professional
Call a pro when you can't find the source, when it's inside a wall or ceiling or when there's a strong odor you can't reach. EcoFusion technicians can locate the problem area, and our wildlife removal team can remove dead animals, find how they got in and seal the entry points.
Blow flies are unpleasant, but they're useful messengers. They're telling you something nearby needs to be removed. Find it, clean up and seal the gap, and the flies stop. If they've shown up in your Cranford home and you can't find the cause, EcoFusion Pest Control can help.