Why LA has daytime ankle-biters now
For most of LA's history, mosquitoes were a dusk problem near water. The invasive Aedes mosquitoes changed that.
Where they came from
Aedes mosquitoes are believed to have reached California more than ten years ago, likely by cargo ship. Over the last decade the yellow fever mosquito spread across LA County, and the state now lists it in 111 county communities. The Asian tiger mosquito has been found in 34 of them.
Why they're harder to live with
- They bite in the daytime. The native Culex mosquitoes mostly bite at dusk and night. Aedes bite all day, often low on the legs.
- They breed in almost nothing. A quarter inch of water in a plant saucer, a bottle cap, a clogged gutter or a toy is enough.
- Their eggs survive drying out. Eggs stick to container walls and hatch when water returns, which is why you scrub the container, not just empty it.
- They stay close to home. They're weak fliers, so the source is usually within a few houses of where you're getting bitten.
- The season is getting longer. They used to disappear from winter until about May. LA's vector control district says that hasn't happened in recent winters.
Health risk
Aedes can carry dengue, Zika, chikungunya and yellow fever. They don't spread West Nile virus; Culex mosquitoes do. LA County has had locally acquired dengue cases in recent years, and public health agencies track every case. If you get a fever, rash or severe body aches after travel or many bites, tell your doctor.
What the districts are doing
Public districts survey neighborhoods, inspect properties, and are testing the sterile insect technique: releasing sterilized males so eggs don't hatch. Early releases in LA County cut female Aedes populations by more than 80% in test neighborhoods. Scaling it up needs more funding.