Notice a lot more mosquitoes last summer? Most are gone now since cooler weather slows them down and reduces their numbers, but they’ll return as soon as it warms up this spring. Time to start planning now. If you’re reading this in the winter, check out how to prepare for mosquitoes before they become a bigger problem.


The arrival of the AEDES AEGYPTI MOSQUITO is affecting our neighborhoods. It’s a huge problem but also a problem that can be helped by making small changes that will result in a better environment for all of us.

First some background and why these mosquitoes are such a problem.

The mosquito we’ve known for years in Southern California is the Culex mosquito. Still here but their eggs need water to survive, they live almost entirely outside but can sneak indoors, they are active mostly at night, and are easier to control just by getting rid of obvious sources of standing and usually stagnant water.  They are also slower and easier to swat.

Around 2001 a new mosquito called Aedes albopictus was detected in Southern California.  Known as the Asia Tiger mosquito, this mosquito was probably a stowaway on shipments of plants from China.  People thought it was under control, but about 10 years later an even worse Aedes mosquito took its place: The Aedes aegypti mosquito.  This one apparently came from South America.  All three mosquitoes and others are now residents of Southern California, but I’m going to focus on Aedes aegypti because it’s kind of a super-villain mosquito with special powers, but it also has special vulnerabilities.


  • Doesn’t need to lay eggs in water.  THIS IS THE GAME CHANGER.  Eggs last up to 5 years and hatch whenever there’s water, which means they can hatch and become adults 5 – 8 days later in places you never expected: rain gutters, underground landscape drains, garden plants that hold water like bromeliads and agave, trashcans, toys left outside, plant saucers and even a single bottle cap.  The old mosquito-fighting strategy of just finding and dumping stagnant water doesn’t work.  You need to do something about anything outside where someday there may be water that doesn’t immediately evaporate and may last for several days after it rains or from watering the yard.
  • Culex mosquitoes mostly come out during evenings or mornings, but Aedes aegypti are active day and night. There’s no time you can avoid them.
  • Culex mosquitoes live outside and only sneak in when they have a chance. Aedes aegypti live outside AND inside.  They can lay eggs in flower vases, toilet bowls, sink and shower drains and anywhere else where there’s standing water.
  • Culex mosquitoes land and bite once so they’re easier to swat. Aedes aegypti (also called ankle biters) fly faster and take several quick bites so they’re harder to swat.  To make things worse Culex mosquitoes prefer birds over humans, while we’re the favorite targets of Aedes aegypti mosquitoes.
  • More about Aedes mosquitoes:


Adult Culex mosquitoes can fly for miles but adult Aedes aegypti usually only fly 100 to 200 yards during their whole life.  This means that most mosquitoes bothering you came from your own property or from your neighbors.  Doing what you can on your own property, and helping or encouraging your neighbors to do the same things will make a huge difference you will notice.

Enjoying our yards is a major benefit of living in Southern California.  We may be losing that because of Aedes aegypti.  There are news reports that unless we do something about these mosquitoes, LIVING IN SOUTHERN CALIFORNIA MAY FEEL LIKE LIVING IN FLORIDA where entire backyards are protected by giant plastic bubbles.  THAT’S REALLY SCARY.

Mosquitoes also carry many serious diseases like West Nile virus and others. For more information see:

When the number of mosquitoes gets too high and/or disease is detected, Orange County Mosquito and Vector Control District may need to spray pesticide in an entire area as was recently done in Santa Ana.

The pesticide (Deltamethrin) is sprayed at night and in small concentrations so to not be harmful to humans or pets.  The pesticide can be harmful to bees and other insects, and is especially harmful to fish in outside ponds. Spraying pesticide is a serious option with serious consequences but may be necessary. 

It’s much better to control mosquitoes early and keep things from getting this bad.


  • Survey your own yard and dump anything holding water (This is the easy part).
  • Remove or turn upside down anything not being used and that may hold water after it rains or from irrigation (toys, plastic buckets, trashcans, backyard “junk” even as small as a bottle cap).
  • Ideally, things that need to hold water (pet water bowls, bird baths, potted plant saucers) should be emptied and scrubbed at least once a week.  For things that can’t be emptied (large bird baths, fountains and ponds) see information re: Bti below.
  • Do you have rain gutters or underground landscape drains?  Rain gutters should be cleaned before our rainy seasonUnderground landscape drains should be flushed out to get rid of even tiny blockages.  It only takes a few leaves to make small dams in rain gutters and underground drains to create huge breeding areas for mosquitoes that you can’t see.  Check your own gutters the next time it rains. Also a huge problem is water condensing on roofs and draining into the gutters, so it’s always important to check your rain gutters every so often.  If water evaporates everywhere in a couple days you’re probably OK. If not you may have a big problem. You will never know what’s going on in your underground drains so they are always a problem area.
  • Bacillus thuringiensis israelensis (Bti): This is as close to a silver bullet to kill mosquitoes that seems to exist.  It’s a naturally occurring soil bacteria that only kills mosquitoes and a few flies but is harmless to other insects, birds, animals and humans.
  • There’s a great overview and explanation of Bti at
  • Bti is available at many hardware stores as “dunks” or “bits” and can be added to birdbaths and fountains where it’s not practical to keep changing the water.  Even OK to use in ponds. It won’t hurt fish. It’s probably even OK in pet water bowls, but personally I think better to just change the water. No matter what scientific studies say, human and animal stomachs may have issues with anything.
  • Bti is also available to commercial applicators in liquid form that can be used to spray entire yards as a precaution, and especially important if you have plants that retain water like bromeliads, agave leaves, etc. One huge caution: LIQUID BACILLUS THURINGIENSIS (BT) MAY BE AVAILABLE IN RETAIL STORES BUT IT ISN’T BTIIt’s probably a related strain of the same bacteria and what’s usually available kills most larvae including butterfly larvae but is harmless to mosquitoes.  MAKE SURE YOU GET BTI AND NOT BT.
  • If you have areas of standing water in rain gutters you can tie a dunk in those places and it will be activated when it rains.  For underground landscape drains and drains under rain gutter downspouts you can add some Bti bits after they’re flushed out.
  • In addition to Bti there is also another soil bacteria that kills mosquitoes but is harmless to everything else: Bacillus sphaericus (B. sphaericus).  Good discussion of both products at There are products available to commercial applicators that contain both Bti and B. sphaericus  – which is what OC Mosquito and Vector Control usually uses in public areas like storm drains and creeks.


  • Change water in vases at least once a week.
  • Make sure drains under sinks and showers are used at least once a week.  Same for toilets.  Problem areas are guest bathrooms that might not get used often and when you’re on vacation.
  • For when you’re on vacation: (Note: I tried Bti inside and it leaves a musky odor so probably not a good option).  There are a couple things I’m trying as an experiment: 1) For drains: Hot Spot, a Bio Sanitation Foam made by Rockwell Labs Ltd.  Specifically made to use in drains, this product cleans and deodorizes drains and isn’t advertised for mosquitoes.  It’s used in commercial and home floor drains to minimize cockroach issues using microbes to digest organic buildup.  It also contains citrus oil which insects don’t like. 2) For toilet bowls: Lysol Toilet Bowl Cleaner.   Again, these products aren’t designed to control mosquitoes.  I’m assuming they will help make the water inhospitable to mosquitoes and not do any damage.  I couldn’t get any recommendations for this issue, so this is just an idea. My first thought was to just add some bleach to the water, but I asked plumbers about using bleach and letting it sit for extended periods, and they said bleach may corrode pipes and etch porcelain. 
  • Mosquito traps are available using UV light and/or C02 to attract mosquitoes.  They actually work well inside and also make you feel safer especially at night.  One mosquito flying around inside can drive you nuts. Some traps zap and disintegrate what goes inside, but they make noise and you can’t see if you’re catching anything.  Non-zapping traps let you test locations to see if and where you might have a problem.
  • There are also larger mosquito traps that work outside and kill lots of mosquitoes.  Every less mosquito helps but you can’t do everything.

Home Inspection Checklist:

There is already much information available re: different types of mosquito repellants so I’m not adding to that except to say that repellants are important and useful to avoid mosquito bites.  There are also new technologies available and still being developed and tested such as and, but these technologies may be too expensive for average people to use.

There continue to be even more types of mosquitoes coming our way, such as Aedes vittatus, that may eventually impact us all.  It’s important to know that the mosquito mitigation efforts suggested above will help control all mosquitoes.  For more information see:

The main season for mosquitoes in Southern California starts around May and continues through October or until the weather gets colder, so there’s still time to make a difference this year  – and to plan for next year.

More information also at the website of Orange County Mosquito and Vector Control District: and 

The main message is that you can continue to enjoy being outside in your yard and be safer from mosquito born disease, and actually make a real and substantial difference, by doing a few things at home and working with your neighbors.