Why does a 67F summer change the treatment math?
Mosquito development runs on temperature. The CDC puts both Culex and Aedes at seven to ten days from egg to flying adult, and that figure assumes warm water. In San Francisco, where summer highs average 67F and fog keeps mornings cool, water in a shaded light well or a north side planter tray sits at the low end of that range, which stretches the cycle. The useful consequence is that your weekly container routine has more slack than it would in a hot inland city. Miss a week and you have probably not lost the season. The misleading consequence is that people assume cool means safe. Humidity averaging 75 percent works the other direction: adult mosquitoes lose water slowly in damp air, so once they emerge they survive longer and keep biting longer. So the local pattern is fewer mosquitoes produced per week, but each one hanging around a while. That favors finding and removing the water over repeated knockdown spraying, since killing tonight's adults does nothing about the small steady supply coming out of a drain you have not found yet.
Where does the water hide on a dense city lot?
Start below grade. Light wells collect leaves and debris, the drain clogs, and a few inches of water sits there through the summer out of sight from every window. Garage sumps are the same story with a pump that may not run often enough. Go up next. Flat and low slope roofs are common in San Francisco, and their drains and scuppers hold water when they partly block. A roof puddle you never see can supply a whole building. Then check the seam between buildings. That narrow side yard gets no sun, drains poorly, and often has an old bucket, a stack of pots, or a piece of plywood lying flat that traps a shallow pool. Finally, look at what people carry outside: deck planter trays, self watering pot reservoirs, a tarp over stored furniture, the tray under a barbecue cover. On a small parcel this whole list takes twenty minutes to walk. That is the advantage of density. The search area is tiny, even if the specific spots are awkward to reach.
Which mosquitoes are actually biting you?
Time of day sorts it faster than anything else. Bites at dusk and just after dark usually mean Culex, the group behind West Nile virus. Culex lays rafts of 100 to 300 eggs on standing water with some organic content, and it will fly up to two miles to find a meal. That range is why a Culex problem can begin at a storm drain or a neglected pool blocks away. Bites in bright daylight point to Aedes aegypti or Aedes albopictus. Both are established in California, and the CDC lists the state among those with limited local dengue transmission from Aedes aegypti. They are small, dark, sharply marked, and they stay put, rarely covering more than a few blocks in a lifetime. Along the bay margins, salt marsh and floodwater species add a third pattern: heavy nuisance biting in pulses after tides or rain flood low ground, with no relationship at all to what is in your planter tray. Knowing which of the three you have decides whether the answer is containers, a report to the vector agency, or simply better screens.
Flats, landlords, and a problem nobody owns alone
In a building split into units, mosquito complaints tend to bounce around until somebody looks at the shared parts. The roof drain, the light well, the garage sump, the side yard, and the gutters are almost always building responsibilities, and they are also where the water usually is. What a tenant controls is short: containers on a deck, a planter tray, whether screens are intact on windows they can reach. The practical move for a renter is to clear your own list first so the remaining problem is clearly structural, then put the shared items in writing with dates and photos. For an owner or manager, one thorough inspection of the shared water beats fielding the same complaint from three units across a summer. It also matters that Aedes travels only a few blocks. If the daytime biting is coming from a neighboring building's side yard, no amount of work inside your own property line closes it out, and a friendly conversation next door does more than another service visit.
A season by season plan for a coastal yard
November through March is the wet stretch, when almost all of the 24 inches of annual rain falls. Nothing bites much, and this is the best time to clear drains, fix a slow light well, and put loose containers away. Water that sits now will still be sitting in April. April and May are the quiet build. Larvae appear in whatever held winter water. A single pass through the property at this point removes a lot of what would otherwise bother you in August. June through August is the active season, and the routine is weekly: check, empty, scrub. Barrier work, if you want it, belongs here. Late August through September is the highest risk window nationally, with the CDC putting the West Nile peak at late August into early September and California reporting its heaviest activity in the same stretch. Pay attention to any county advisory. October tapers off. By November, biting mostly stops, though the eggs on dry container walls will wait patiently for the rain to come back.
How do you tell a real plan from a spray schedule?
Ask four questions and the difference shows up quickly. What water did you find? A provider who inspected a small city lot should be able to name specific spots: the light well drain, the trays on the deck, the sump. Vagueness here means nobody looked hard. What gets larvicide and how often? Below grade water needs treatment on its own cycle, usually every three to four weeks, and that is separate from any spraying. What is the plan for daytime bites? If you reported noon biting and the answer is a shrub application, the method does not match the insect. What is not included? Roof access, screen repair, and drainage fixes usually sit outside a standard quote, and on this housing stock those are often the actual solution. Prices vary mostly with how much of the building has to be inspected and whether there is permanent water to treat, so compare scope before comparing figures. A cheap quote that only covers a fifteen foot strip of shrubbery is not cheaper, it is smaller.