The mosquito that bites you at dusk was probably born within 50 metres of where you are standing. Most domestic mosquitoes do not travel far. They do not need much water either: a bottle cap is enough for a brood.
The cycle, in days
A female lays 100–300 eggs after a blood meal. Aedes species lay eggs singly on damp surfaces just above the waterline; the eggs survive drying for months and hatch when water rises. Culex species lay rafts of eggs directly on the surface.
Larvae filter-feed for about 7–10 days in warm weather, then pupate for two days, then emerge as adults. From egg to biter in under two weeks. In cool weather the same cycle stretches to a month.
The containers people miss
- Plant saucers. The single most productive site in most gardens.
- Tarpaulin folds. A crease in a pool cover or a boat cover holds water for weeks.
- Gutters. A blocked downpipe keeps a reservoir at roof height, out of sight.
- Buckets, wheelbarrows, bird baths, pet bowls. Anything that holds water for seven days.
- Drains and sumps. Culex breeds in standing water rich in organic matter.
What actually reduces the population
Empty and scrub. Aedes eggs stick to the container wall and survive a simple rinse; scrubbing removes them. Do this weekly through the season, which is faster than the egg-to-adult cycle.
For water you cannot empty — a rain barrel, a pond, a drain — use a larvicide containing Bacillus thuringiensis israelensis (Bti). It is specific to mosquito and blackfly larvae and does not harm fish, birds or bees. Mosquito dunks last about 30 days in standing water.
What does not work
Bug zappers kill far more harmless insects than mosquitoes, and ultraviolet light is a weak attractant compared with carbon dioxide. Ultrasonic repellents have no reliable evidence behind them. Fogging a garden kills the adults present and does nothing to the larvae in the saucer.
The 10-minute weekly walk
Once a week, walk the garden with a bucket and tip out every container you can lift. Empty the saucers, straighten the tarpaulin, clear the gutter, refresh the bird bath. Ten minutes a week removes more mosquitoes than any spray, because it removes the next generation before it can fly.