Updated May 9, 2021. Short version: dump standing water; larvicide water that can’t be dumped.
But that photo shows mosquito larvae, which don’t bite.
Right, but once larvae hatch, they are harder to control. One female mosquito, with a protein infusion from blood, lays 100+ eggs. The eggs hatch into larvae, which fly away as adults in a few days.
Mature larvae are very noticeable, about 3/8 of an inch long and quite active looking for feed in unclean water. But just because you can’t see larvae doesn’t mean they aren’t there; they start out really tiny but grow rapidly.
Can’t we just spray and kill all the mosquitoes?
Air-borne insecticides, a temporary fix at best, may with luck kill 80% of adult mosquitoes flying in the vicinity, but do not affect eggs, larvae, or pupae (the larvae who have already moved to a cocoon-like phase). Within a few days, the population is restored. Besides, many mosquitoes can fly half a mile or more and will quickly occupy any temporary gaps.
And even worse, sprays kill many insect species, including bees and insects like dragonflies that eat mosquitoes! Also, the more we spray, the more likely mosquitoes are to become resistant to the insecticides we use, and then we will be in trouble in a real emergency (as happened in Miami in 2016).
See more answers to the question “Why don’t they just spray and kill all the mosquitoes?” here
So what do we do?
We must eliminate stagnant water! It sounds easy but requires imagination. Empty out birdbaths, pails of water, saucers under plants, trash and recycling containers and lids, and whatever else can hold water. Spill out ALL standing water every 3-5 days to be safe.
And look overhead: be sure your house eaves drain properly. If they are blocked, remove the blockage. If they don’t slope properly toward the down spout, try to adjust the slope or add a new down spout in the low spot.
For a few “Case studies in what to avoid,” click here.
How about larger bodies of water like ponds and streams?
A biological agent called Bti, inexpensive and widely available in hardware stores and elsewhere, prevents larvae from growing into adults. See more here. If the water is actively running, no problem; but look for stagnant areas of streams, especially where water is blocked at the surface or where pipes come in at surface level and may contain motionless water.
Larvicide only your own property, or help someone else to do it on theirs. Swimming pools usually have enough chlorine to kill larvae, but swimming pool covers can hold water and breed mosquitoes..
How about mosquito repellents?
By all means, experiment with natural oils and granules. But we do not recommend applying substances like DEET to your skin or clothing; there is too much potential chemical exposure to hypersensitive individuals, babies and children, and pets.
Where can I get more information?
Chester County has two relevant web pages, one on avoiding mosquito-borne diseases generally and one more specifically West Nile Virus (a mosquito-borne disease that is very rare here). Both stress how to keep mosquitoes from breeding on our property.
It is against County health regulations to maintain a “receptacle or system” capable of breeding mosquitoes; if you see a property violating the regulation, please talk to the property owner and/or contact the municipality or the Chesco Health Department.
And talk to your neighbors, especially any who may be thinking of hiring a mosquito control company… and who may need some of the information above. Especially, they should read the safety sheets on all chemicals the company says it plans to spray.