How Are Maggots Formed? The Life Cycle of Flies Explained

How are maggots formed? They are not made by rubbish or rotting food on its own. Maggots are the larvae of flies, and they hatch from eggs that adult flies lay on rotting food, animal waste or carcasses. In warm weather the eggs can hatch within a day, producing the small, pale, legless grubs most of us find unpleasant. Stop the flies reaching the food and you stop the maggots.

The old myth of spontaneous generation

For centuries, many people believed that living things could arise from decaying matter. Maggots seemed to prove it, as they would turn up in rotting meat as if from nowhere. In the seventeenth century, the Italian physician Francesco Redi tested the idea. He placed meat in jars, leaving some open, covering some with gauze and sealing others. Maggots appeared only where flies could reach the meat, and flies had been seen landing on the open jars. The experiment is a classic example of an early controlled test, and it pointed to flies as the source. You can read more on Francesco Redi on Wikipedia.

The fly life cycle

1. Egg. An adult female finds a suitable food source such as meat, fish, food waste, pet food or manure, and lays batches of small, white eggs.
2. Larva (maggot). The eggs hatch, often within hours to a day depending on species and temperature. The maggots feed and grow, shedding their skin several times.
3. Pupa. When fully grown, the maggot leaves the food, often seeking a drier place, and forms a hard, brown case.
4. Adult. After a few days to a couple of weeks, an adult fly emerges, and the cycle begins again.

Heat quickens the whole process and cold slows it. In hot weather a bin can go from clean to crawling in a few days, while in winter the same waste may hardly be touched.

Where maggots turn up at home

• Bins, especially those holding meat, fish or pet food scraps.
• Compost heaps and food waste caddies left uncovered.
• Pet bowls and litter that have not been cleaned.
• Dead animals, such as a mouse in a wall space or a bird in the garden.
• Forgotten food in a cupboard, a bag of shopping or a fridge that has failed.
• Drains with a build-up of organic matter, which can attract small flies.

If you find several maggots indoors with no obvious source, it is worth looking for something dead behind appliances, in loft spaces or under floors.

Different flies, different habits

Fly	Typical breeding material	Notes
Bluebottle and greenbottle	Meat, fish, carcasses, bin waste	Fast to find food; often the culprits in bins
House fly	Manure, rotting waste	Common near animals and compost
Flesh fly	Carrion, waste	Sometimes lays live larvae
Fruit and drain flies	Fermenting fruit, sludge in drains	Produce much smaller larvae

You do not have to identify the species to deal with the problem. The same clean-up and prevention steps work for all of them.

Getting rid of maggots

1. Wear gloves and bag up the source: the waste, food or object they are in. Tie the bag and put it in an outside bin.
2. Pour boiling water over maggots on hard surfaces such as a bin base or a patio, if it is safe to do so. Take care with scalds.
3. Wash the bin with hot water and detergent, then rinse, dry in the sun and consider a disinfectant.
4. Wipe the area and nearby surfaces with hot soapy water, and vacuum any that have wandered, emptying the vacuum straight away.
5. Clean the cause: spilled liquid, pet bowls or the corner of a cupboard.
6. If the source is a dead animal in the building or you cannot find it, contact pest control or your local council.

Maggots in an outdoor bin are common and generally harmless, but they are a sign that the bin needs more care. Maggots in an indoor kitchen mean you should check stored food straight away. Although they rarely bite or sting, flies and larvae can carry bacteria, so wash your hands and keep food covered. If you are looking for tiny pests in other parts of your home, see our guide to little black oval bugs in the house.

Preventing maggots

• Use bins with tight lids and keep them out of direct sun when possible.
• Wrap meat, fish and pet food scraps in sealed bags before binning, and freeze them until collection day in summer.
• Wash bins regularly, especially after emptying.
• Keep food waste caddies lined and emptied often.
• Cover compost with a lid or a layer of dry material, and avoid adding meat or fish.
• Clean pet bowls and litter areas daily.
• Use fly screens on windows and doors in warm weather.
• Keep the fridge cold enough to protect food. See our guide to average fridge temperatures for the settings to aim for.

Maggots and animals

Flies sometimes lay eggs on living animals, especially on soiled or wounded fur, and this condition, called flystrike, is a veterinary emergency. Sheep and rabbits are affected most commonly, but dogs and cats can be too. If you see maggots on a pet, contact a vet immediately. For a related pet topic that also needs prompt attention, our piece on a tick head left in a dog explains when to call a vet.

When maggots are useful

Maggots are not only a nuisance. Fly larvae break down dead plants and animals, returning nutrients to the soil, and some species are farmed as feed for fish and poultry or as bait for anglers. Sterile, specially bred larvae have even been used in medicine to clean certain stubborn wounds, a practice with a long history. None of that makes them welcome in the kitchen bin, but it explains why entomologists regard them as a vital part of natural recycling.

Frequently asked questions

Conclusion

Maggots come from flies, not from rot itself. Keep flies away from food and waste, clean up promptly in warm weather, and you will rarely meet them.