Flies in the house and garden: where they come from and how to catch them

On a warm day they are suddenly everywhere: flies around the barbecue, on the patio, by the compost bin or in the stable. Usually they are houseflies and bluebottles. They follow their nose and breed in anything that rots or ferments. Remove the breeding spots and put a bait trap outside, and they will bother you a lot less.

Which flies do I have?

Around the house and garden it is mainly two kinds. The housefly is grey, about 7 mm long, with four dark stripes on its thorax. The blowfly, better known as the bluebottle or greenbottle, is bigger, shiny blue or green, and makes that familiar heavy buzz. If you see small flies around fruit, they are fruit flies; if they come out of the compost of your houseplants, they are fungus gnats.

What attracts flies and where do they come from?

Smell. Flies look for protein and sugar and lay their eggs in moist, rotting material: food waste, the compost heap, manure, dog mess, meat and fish scraps and leftover wet pet food. An open bin in the sun is a nursery for a fly.

When are there the most flies?

In the warm months. Above about 15 °C flies become really active, so from April to October. You see the most in a warm week after rain, when rubbish and compost start to ferment quickly.

How fast do flies multiply?

Very fast. A housefly lays hundreds of eggs in her short life, and in warm weather an egg becomes a new fly in about ten days. That is why in summer they seem to appear all at once. Catching flies early in the season removes the next generations before they exist.

Are flies harmful?

Flies do not sting, but they walk over rubbish and manure and then over your food. That way they can spread bacteria. So always cover food outdoors.

How do you catch flies outdoors?

With a bait trap that smells of what flies are looking for, such as protein and yeast. A bait trap draws flies in, so where you put it matters most:

1. Outside and away from where you sit. Place it at the edge of the patio, by the compost bin, the wheelie bins or the stable door.
2. In warm weather in a tree, in cool weather in the sun. Warmth spreads the scent, but in full sun at the height of summer a liquid bait dries out faster.
3. Several traps at least two metres apart.
4. From April. Starting early in the season catches the first flies before they multiply.

How do you prevent flies?

1. Keep rubbish covered. Bins with lids, and food waste preferably out of the sun.
2. Cover the compost heap and mix fresh kitchen scraps into the existing material.
3. Clear up dog mess and manure quickly, also around the stable and the hutch.
4. Do not leave food or pet bowls outside.
5. Fit fly screens on windows and doors, so flies cannot get in.