Last Updated: 10/31/13
Mosquito Control and Breeding
Mosquito Dunks, Bt, and Deterring Mosquitoes
Spraying and Your Pond
This page is about mosquitoes and their part in a functioning, healthy watergarden.
For another view point on mosquito control, see this contributing article on mosquitoes.
Mosquito larvae range from 0.2 to 0.5 inches long. They are called wrigglers because they wiggle around when disturbed. They usually stay at the surface with their breathing tubes sticking out of the water. If you are unsure if there are mosquito larvae in some still water, blow on the surface; if there are larvae, they will wiggle all around. They eat small animals, plants, and debris with the aid of mouth bristles. The pupae are called tumblers since they wiggle around when disturbed. Their head and thorax are fused but they can swim. Adult females need blood while males eat nectar and fruit. Females lay eggs in rafts on the water surface. Eggs hatch in 1 to 5 days. Larvae pupate in one to two weeks. Adults are 0.2 to 0.3 inches long. There are 120 species of mosquito in North America. The house mosquito is Culex pipiens.
Most often, people want to know about mosquito control. Female mosquitos bite mammals and birds and feed on their blood to nourish their eggs. They also feed on humans, leaving welts and sometimes (rarely!) transmitting malaria, yellow fever, encephalitis, West Nile virus, or other diseases. The female mosquito lays a raft of tiny eggs in still water which hatch into wriggling larvae. After a few weeks, these leave the water as adults. You can control mosquitoes for sure one of two ways (mosquito-eating fish or mosquito dunks). First, add small insect-eating fish like young goldfish, fathead minnows, mosquito fish, etc. (see here for information of these and other fish). See the next section for the information on dunks and other methods that work sometimes.
If you raise aquarium fry outdoors, expect mosquito larvae to appear unless you add mosquito dunks, at least until the fry are large enough to eat the larvae. Adult aquarium fish love the larvae so some people get mosquito larvae just to feed their fish. One person who e-mailed me was all excited about the wriggling "baby fish" they had gotten from their aquarium waste water. When she said they folded in half and squiggled to move, I knew what they were. I told her to feed them to her fish who had a treat.
If you prefer a fish-less pond or one with large fish like adult koi who will not keep mosquito larvae under control, then you can add what are called mosquito dunks. These contain natural organisms (Bt bacteria, Bacillus thuringlensis) which attack mosquito and similar fly larvae but will not harm non-insect animals or plants in any way. They can be ordered through many of the catalogs which I list at my pond catalogs page. The place that makes them is Summit Chemical. Their web site has tons of information on mosquitoes and their mosquito-killing products but you cannot order direct from them.
In addition to the mosquito dunks, they sell faster acting mosquito bits and now liquid Bt sold by Microbe-Lift. The liquid version is great when you do not want bits of corn-like stuff floating around in your pond. I use it for my tub ponds. Here are some photos of the various Bt products from Drs. Foster and Smith. Drs. Foster & Smith deleted their affiliate program so these links will no longer work. I am leaving up the pictures which are still working for now.
Also, increasing water movement and depth deters mosquitoes. Most larvae need still water to breathe so they would not be found near waterfalls or other moving waters. Stagnant, yucky water is their favorite hang-out. You will not find mosquito larvae around gushing water! Add air stones, waterfalls, fountains, etc.
Another way to reduce mosquito larvae numbers is to smother them by planting tight growing floating plants. This is not advisable in fish ponds since it can also reduce oxygen content for the fish. It works well in tub ponds. Azolla or Fairy Moss, Azolla caroliniana, is also called mosquito fern since it can grow so dense as to stifle out mosquito larvae.
In addition, promoting adult mosquito predators can help keep mosquitoes under control. Swallows, bats, and dragonflies are three animals that love to eat adult mosquitoes. Putting up bat and bird houses can thus help keep mosquito numbers down. Some insect larvae also eat mosquitoes including dragonflies, phantom gnats, and more. Promoting a wide array of insect life helps to prevent an outbreak of any one species. Dragonfly larvae are big eaters of mosquito larvae. Adult dragonflies are also called mosquito hawks. For more on dragonflies, see my dragonfly page.
Summary of how to deter or prevent mosquitoes:
Unfortunately, people become paranoid about mosquito-borne diseases. The West Nile Virus was the big scare for a while. By following the above advise, ornamental ponds should not be a major contributor to the mosquito population. The facts include that only a small percent of mosquitoes in certain areas carry the West Nile Virus, only a small percent of those transmit the disease in the process of biting a human, only a small percent of people who contract the virus actually get ill, and only a few people (young, old, those with compromised immune systems) die. By avoiding the outdoors at dawn and dusk and after dark during certain times of the year, by wearing long pants and shirts, and by using insect repellent sprays, the chances of being bitten are greatly reduced. Bug zappers have been shown to include a kill which is comprised of less than 1% mosquitoes, and the vast majority of victims are beneficial insects including those that would have eaten mosquitoes. People also do not realize that mosquitoes have some beneficial qualities mainly as food sources for fish and aquatic insects as larvae and for dragonflies, other insects, and bats as adults.
The biggest problem occurs when most people want to spray. Whether sprayed from truck or plane or used to control mosquitoes, Gypsy moths, or any other "pest" insect, these sprays do much more harm than good the majority of the time. If a pesticide or other chemical kills mosquitoes, it is guaranteed to kill other flies (good and bad) and most likely all other insects, sometimes fish, and often amphibians. Permethrin was used in Baltimore, MD in the fall of 2000. They said on the news, "Yes, this kills fish." That includes any fish in ornamental ponds. The spraying also kills the dragonflies and other predators of mosquitoes as well as beautiful butterflies and other beneficial insects. The Merck index (a reference book for chemists) says that permethrin kills fish and bees (honeybees are already in dire trouble from mites and ants and now in 2013 colony colapse from pesticides). If spraying is slated for your area, it may be necessary to move all fish (and maybe other animals as well) indoors. If this is impossible, carbon can be run through the filter to try to filter some of the poison out. At least one person has reported a 100% fish kill after aerial spraying for insects elsewhere. Poisoning all life is not the answer! Many chemicals used are said to be safe for humans but how safe is a crashed, polluted, dead ecosystem to live in? The newspaper says that permethrin can cause burning, itching, numbness, and respiratory problems in humans but that it is "okay" because these symptoms only last a day.
A report came out in 2001 about the West Nile Virus as studied in tens of thousands of dead birds. The study showed that while some of the birds died from the virus (which is 100% lethal in crows), the leading cause of death was pesticide poisoning. Many of these chemicals are used by uninformed people on their lawns. Frank Gill of the Audubon Society said, "Millions of us use pesticides...at home...We deserve to know as much as possible about their effect on us. Like canaries in a coal mine, birds warn us of danger in our environment. If these chemicals kill birds, what are they doing to our kids?" To see this article, go to http://ens.lycos.com/ens/jun2001/2001L-06-22-06.html. This site no longer works but I am leaving the link (the site is not in archive.org either). I certainly try to avoid using any pesticides on my property. And yet, with all my ponds and land, I only get a few mosquito bites per year. This is because we do NOT use pesticides which allows the other insects and animals to consume the mosquitoes without being poisoned themselves.
Drawings of a mosquito larvae and an adult can be seen at this water bug site.
Drawings of a larval and adult mosquito can be seen at this site. This is an archived version of the site as it no longer exists.
Visit Beyond Pesticides: National Coalition Against the Misuse of Pesticides for pesticide information.
Visit the Monmouth County Mosquito Extermination Commission for information on mosquito-borne diseases and mosquito control via pesticides. This is an archived version of the site as it no longer exists.
Mosquito Control Information from Montgomery County, Maryland; includes many West Nile links. I like this site because it does not tell you to get rid of your ponds but rather to keep them stocked with fish and/or keep the water moving! This is an archived version of the site as it no longer exists.
West Nile Virus: How Vulnerable Are We? - this is an archived version of the site as it no longer exists.
Safe Mosquito Control - this is an archived version of the site as it no longer exists.
Mosquito Larvae Photos - this is an archived version of the site as it no longer exists.
Summit Chemical - sells Bt products that kill mosquitoes but few other animals (just other similar fly larvae).
No Spray News - a site on the ills of spraying pesticides for mosquito control.
Alamada County (CA) Mosquito Abatement District - mosquito and mosquito fish information (they will give mosquito fish to those in their district).
Pesticides and Safe Alternatives - includes web site links
Return to the main insect page.
See the master index for the insect pages.
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