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I found lots of mosquito larvae in my fountain. How can I get rid of them?

A local store has the doughnut thingies but they are expensive. I'd prefer a homemade solution if possible.

I tried vegetable oil. It worked but looks ugly.

Any other suggestions?

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6 Answers

up vote 18 down vote accepted

Vegetable oil does not work well because it beads up on top of the water and does not spread across the surface. It also goes rancid.

Mosquito larva breathe air through a little tube while they float on the surface, so "oil" remedies are designed to cut off their air supply. You can try a horticultural spray oil. It only takes a few drops to form a microscopically thin sheen across the water. This is recommended for bird baths so it's pretty safe for the innocent bystanders in your yard.

You can also try mineral oil; Completely non-toxic. There are also non-chemical larvicides (that are mostly mineral oil) that are made specifically for this.

These pet-safe mosquito dunks contain Bacillus thuringiensis (Bti bacteria) which mosquito larva eat and die but it is completely harmless to everything else: pets, birds, wildlife, etc.

If your pond water is otherwise healthy, you can always try raising some fish. Goldfish, koi or, yes, even the aptly-named "mosquitofish" love the stuff.

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I will try the horticultural spray.I thought of getting fish but I worry that the temperature will vary too much for them. My fountain only holds about 10 gallons and gets quite hot in summer. –  Kevin Lawrence Jun 30 '11 at 18:41
    
I asked in the store about goldfish but the lady told me I need at least 50 gallons. My 10 gal estimate is probably very low, but I doubt I have 50, sadly. –  Kevin Lawrence Jul 7 '11 at 19:16
    
I don't know how different mineral oil is from kerosene, but two tablespoons of the latter has always worked in our rainwater tanks. –  Lisa Jul 27 '11 at 1:53
    
I got some horticultural spray. Works great. Thanks. –  Kevin Lawrence Sep 20 '11 at 16:29
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You don't have fish living in it do you? If not, I would drop some pool chlorine in there.

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No fish. Chlorine sounds worth a try. –  Kevin Lawrence Jun 30 '11 at 18:45
    
If you get some chlorine tablets for pools, they dissolve slowly over serveral days (typically), so they keep the chlorine level above a certain concentration for an extended period of time, which makes sure everything gets killed off. –  msemack Jun 30 '11 at 18:51
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@Kevin Lawrence: Just be careful. Chlorine could damage any plastic or rubber plumbing, gaskets, and pump mechanisms if they were not designed for such environments. –  Robert Cartaino Jun 30 '11 at 18:53
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Probably the only way that you'll combat the larvae without adding anything to the water (mosquito eating fish, those donuts) is by draining and refilling the fountain on a regular basis. Unfortunately, most of the recommendations I've heard speak of daily changing (can't find any references at the moment). The aquatic life cycle of mosquitoes is 5-14 days, so you might be able to get away with changing the water every few days. I've also heard recommendations of aerators, waterfalls, or anything else that keeps the water moving (I'm assuming your fountain has some kind of feature like that already?), but I'd guess it would need to be fairly aggressive in the amount of water it churns to minimize mosquitoes and their larvae.

I'm guessing it's going to take you a bit of trial and error to figure out what minimizes the both mosquitoes and the inconvenience of having to battle them. You may even want to just let it sit dry during the worst times of the season.

And make sure you and your neighbors minimize any other sources of standing water around your yards!

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I think fish would be a good solution, but not goldfish. They are nasty, producing lots of feces. If you put a Plecostomus in there, it would eat the algae, and I have read that zebra striped Danios will ferociously eat mosquito larvae. I am looking for solutions before I put in my water feature, I'm no expert. I think the oil would just look gross. Hats off!

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I have found only one solution to mosquito larvae.

  1. Drain your fountain once. Use a shop vac to remove leaves, debris and dirt.
  2. Let it dry in the sun for one day (if you are patient).
  3. On day two, refill with water, and place a jacuzzi chlorine float in the basin. Close the chlorination vents so your chlorine is not dispensed too fast. Chlorine tablets are the size of wine bottle corks (available at big box home improvement store, or pool supply).
  4. Set your fountain timer to operate at least a few hours a day to cycle the water (I run ours from noon to 10pm for ambiance).
  5. Once a month, top off the chlorine float.

You will never have mosquito larvae again.

I keep my chlorine levels high enough where you can smell the chlorine on your wet hand. I would rather have a sparkling clean fountain and replace my pump and parts once every five years, rather than change my water once a month because of larvae.

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Can you drain the fountain? If yes, then drain the fountain and pour antiseptic on the fountain. I cannot think of other method. I won't put a fish into fountain.

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I drain the fountain quite often - mostly to get rid of algae - but the larvae come back. –  Kevin Lawrence Jun 30 '11 at 18:43
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