San Francisco Bay and East Bay Area

That's the signature of invasive Aedes mosquitoes. Invasive Aedes mosquitoes are aggressive daytime biters and have spread across the Bay Area since 2013. Unlike traditional Culex (which feed at dusk and dawn), Aedes are most active in the late morning and afternoon. They also bite low, usually around the ankles and calves, often while you're sitting still on a patio. If your bite pattern has changed in the last few years, this is almost certainly why.

The realistic local risk is West Nile virus, which shows up every summer in the Bay Area — Santa Clara and Contra Costa counties typically report cases each year. Most people who contract West Nile have no symptoms or only mild flu-like illness, but serious cases happen, especially in older adults. The invasive Aedes mosquitoes are capable of transmitting Zika, dengue, and chikungunya, though local transmission of those in the Bay Area has been very rare so far. Dog owners should also know mosquitoes can transmit heartworm; heartworm prevention is worth a conversation with your vet.

Because mosquitoes need shockingly little water to breed — invasive Aedes can complete their full life cycle in as little as a bottle cap of water. Common hidden sources we find during inspections: plant saucers, clogged gutter sections, tarp folds, kids' toys left outside, bird baths that haven't been refreshed in a week, sagging hoses, the inside of corrugated drain pipes, and crumpled tarps in the yard. And even if your yard is spotless, your neighbor's may not be — Bay Area neighborhoods with closely spaced lots usually share a mosquito population.

Three parts working together. Source reduction — your technician walks the property looking for hidden water sources and either eliminates them or treats them with a larvicide that kills mosquito larvae before they hatch. Barrier spray — a long-residual treatment applied to the underside of leaves, shrubs, fence lines, and other shaded resting spots where adult mosquitoes hide between meals. Larvicide stations — for breeding spots that can't be eliminated (like ornamental ponds), biological products keep larvae from developing into adults. The combination drops the population across the whole property, not just the spot you sprayed yourself.

A typical barrier treatment lasts 3–4 weeks depending on weather — heavy rain shortens it; hot, dry stretches extend it. Most properties get treated monthly during mosquito season (roughly April through October in the Bay Area). One-time treatments work great for events — a barbecue, wedding, graduation party — but the recurring monthly plan is what keeps your yard consistently usable through the whole summer.

This is a real concern and one we take seriously. We avoid spraying open flowers and active blooms, treat in the early morning or evening when bees and butterflies are less active, and choose targeted product types rather than broad-spectrum applications. If you have bee hives, a pollinator garden, or major flowering plants in active bloom, tell your technician up front and we'll plan the treatment around them — sometimes that means treating only specific zones of the property.

Peak mosquito season runs roughly April through October, with the worst activity typically June through September. Invasive Aedes can stay active into November in mild years. The season has gotten noticeably longer over the past decade as winters have stayed warmer — we now see service calls into late fall and very early spring some years. If you've had mosquito problems before, scheduling your first treatment in early spring (March or April) stops the population from establishing for the season rather than chasing it after it's exploded.