Saturday, November 14, 2009

Tiny Black Bugs - Fruit Flies or Fungus Gnats?


In lieu of a dog or cat, we have various insects living at our house. Most prominent lately have been these tiny black flying things. But they're too small and too active to really get a decent picture. But this week I found one floating in a little water at the bottom of a cup on the table. These guys sometimes seem to come home with bananas and they like any kitchen scraps we haven't covered well before taking them out to the compost. And we're at the season change time when our backyard compost takes its winter break and we haven't quite gotten used to the garbage disposal yet.

But with a picture in hand, I finally called Cooperative Extension to see if I could identify the little critters. Because they liked the fruit he thought they might be fruit flies, but when he saw the picture he called to say they were Fungus Gnats.

He sent me a link to the Colorado State  Extension site where I learned:

Fungus gnats (Bradysia species) – also known as dark-winged fungus gnats, are small, mosquito-like insects often found in homes and offices, usually in the vicinity of houseplants. They are considered a nuisance when present in noticeable numbers, but the adults are harmless insects that do not bite. Fungus gnat larvae develop in the growing medium of houseplants and are considered minor pests of houseplants. . .

They are really small, I took another picture with a grain of uncooked rice floating next to it.
The most important strategy to minimize fungus gnat problems associated with houseplants is to allow the growing medium to dry between watering, especially the top 1 to 2 inches. The dry-growing medium will decrease survival of any eggs laid and/or larvae that hatch from the eggs as well as reduce the attractiveness of the growing medium to egg-laying adult females. In addition, it is recommended to re-pot every so often, particularly when the growing medium has “broken down” and is retaining too much moisture. Furthermore, be sure to remove any containers with an abundance of decaying plant matter such as decayed bulbs and roots, which provide an excellent food source for fungus gnat larvae. . .

 Want to see if there are larvae growing in your potted plant soil?  But do you really want to find these guys?  (The larvae picture - on a potato - is from the Colorado State site.)


"An effective means of detecting the presence of fungus gnat larvae is to insert 1/4 inch slices or wedges of potato into the growing medium. Larvae will migrate to the potato and start feeding within a few days. The potato slices should be turned over to look for larvae present on the underside."
And the fruit fly?  That looks totally different.  Picture and text are from an Oklahoma State webpage


Life Cycle: Female fruit flies lay their eggs on the surface of rotting fruits and vegetables. Each female may lay as many as 500 eggs. These eggs hatch into larvae which molt twice before becoming fully grown. The larvae feed on the yeast organisms and fungi growing in infested material, and through their feeding efforts, they soon turn their food into a semi-liquid "mess." When the full-grown larvae are ready to pupate, they leave the food material for dryer areas. Complete development from egg to adult under summer conditions may be completed in 8 to 10 days. Mating takes place soon after adult emergence, usually within a few hours, and egg laying begins about 24 hours later.
There's a lot more on the links if you want to know more. 

21 comments:

  1. Could you save me one of those bugs Steve? We just bought a great microscope and I'd love check them out up close.

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  2. I had these little buggers once and found they came from the potting soil I bought at Fred Meyers. I had bought several bags and repotted all of my 79 house plants OMG what a disaster. I had to buy all new soil, wash the roots of all my plants and sterilize all the pots. Now I check the soil before buying it and never buy it from FM's.

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    1. NEVER buy organic potting soil for inside plants - I learned THAT the hard way! Too bad the bags don't say that, since we all think we're doing the best thing.... Kate

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  3. does anyone know how to get rid of them using household prducts?

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    1. I have fungus gnats every summer during compost warm weather, but they usually leave when it gets colder.. Apparently they love fungus for their babies, and I heard cinnamon will stop any fungus growing, so I sprinkle cinnamon on the plant soil, and they just left in a hurry.. Do not leave any moist foods around, as they may also plant the fungus there for the babies... so if I have some moist foods , I just sprinkle the cinnamon on the apple slices etc... or even a stir fry for later... hope it helps a bit. They seem hard to get rid of, as there is always an onion or potato going bad for them to take the fungus to a better place, I imagine this.. not sure they do... mary.

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  4. I have one of thse little critters. No matter what I do I can't get him. Please tell me how, he is driving me crazy. I think I have caught him, but then I open my hand or the place where I hit him and he is not there. There has got to be a way to kill these annoying, pesky little things.

    navygirl

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  5. Couple of suggestions:
    1. put a very ripe banana into a deep pot and hope the bug goes to the banana. Then put on the lid and take it outside.

    2. use a vacuum cleaner to suck it up

    3. go on a vacation and it will be gone when you get back

    Good luck.

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  6. I work for Orkin... best way to get rid of fungus gnats is to stop watering the plant for a while. They're there because of the excess moisture that can exist in potted soil. They thrive off of it. Stop watering, let the dirt really dry out, and you'll find they don't come around anymore.

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  7. fruit flys love red wine. Leave a cup or open bottle of red wine and you'll be amazed how many you will catch (they will drown) in the red wine.

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  8. All you have to do is take a small container about the size of a pudding cup and put about a half inch of cider (orange) vinegar in the bottom, add a pinch of sugar to make it sweet and it will attract the flies/gnats then add 3 or 4 drops of dishwashing liquid to the vinegar mixture. The dish soap cuts the surface of the liquid and they cannot fly out - they drown. If you have fleas that you take off your dog or cat, you can put a small cup with water and 2-3 drops of dishsoap in that and then put the fleas in it as you pick them off your pet. They sink like stones and drown. Clean, Green and takes care of your problem without pesticides.

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    1. I accidently left 1/2 inch beer in a can for a few days, and when I dumped it in the sink to rinse out, , many fungus gnats dropped out. about 30 or more.. so now I leave some around the door where i think they come in from the compost bin in back yard. If you want to protect food from their fungus spreading habits, sprinkle a bit of cinnamon over it.. they all run away because they live off fungus, and spread it around to lay their babies in. The wine is a great idea and does catch a lot... a narrow top would be better I think , as well. good ideas thank you. I heard that sprinkle of basil on food keeps fungus away. maybe many herbs do.. I wonder if cinnamon would work on fruit flies too?? What about flies around worm composting bin?? just wondering if anyone has worked with these?? ., and would cinnamon harm the worms ?

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    2. Thanks for the beer and cinnamon tips. I'll definitely try the cinnamon.

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  9. Anon Sept 5, Someone just told me a very similar methods, except he added a cover to the jar - I don't recall if it was saran wrap or just plastic bag - and poked little holes in. They could get in, but if they could still fly, they couldn't get out. I did a simpler method at my mom's when there were scads of them. Just put some fruit in a plastic back with the opening up in the air and made small. Then when there were a lot in the bag, I just squeezed it shut and took it outside. Thanks for commenting.

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  10. How long will I have these things!! I bought Knat/Fly ruit fly traps today. They are covered with these things. How do you keep them gone? Do they bite? HELP they are gross!

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  11. Anon, sorry about your infestation. I don't think I can add more advice than is already there among the comments. Good luck.

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  12. Help! What I have is something quite different. They are black, about an 1/8" long with translucent wings that may have spots on the tips. They do seem to be some type of fly. They swarm and they seem to appear only this time of year (November). They are outside, not inside, but my doors and windows become covered with them. When a door or window is open, they do come inside but do not seem to fly around too much inside. They mostly congregate near openings. They will fly up around your head, somewhat like gnats, when you through a swarm. I had this problem at a former house I owned, and I've seen them in windows of commercial buildings.

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  13. Anon 11/5/12, Sorry to hear about your infestation. I'm not really an expert on this. And you don't say where you live. If in the US, I'd suggest you contact your local Agricultural Extension Service. Here's a webpage where you can locate your local office:
    http://www.csrees.usda.gov/Extension/

    Since you have so many of them, I'm guessing you could catch a few to show them. But if there are so many, I bet they will know. Let us know what you find out.

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  14. i have what looks like fungus flies. They come into two windows in our home around the same time each year. They don't bite and their life span is very short, but there are hundreds of them and they are annoying.

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  15. I have them. This is the first year. They are not fruit flys. The do like water though. The dogs bowl, the dish drainer. I find them dead every morning. They fly around us too. Won't go after the vinegar water trick.

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  16. mine don't go after the vinegar water either. I've had them for years, but this year they are worse than ever. I thought they were drain flies but they are never near the drains - i never see them around fruit, and I'm a fanatic about food and garbage lying around. I also have many houseplants and one in particular that I brought in from the garden in the fall. It was just too beautiful to see it die off. I finally decided I had to do something about these little devils - it's embarrassing to have them flying around guests. I finally got a close up picture of a dead one and compared it to the photos of a variety of little flies shown on the web - eureka! it's a dead ringer for a fungus gnat. I just ordered something on amazon that's guaranteed to eliminate them - we'll see. I'll report back if they work

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    1. Good luck jpallen. Waiting for your follow up report on what you used. I'm leery of chemicals. I've found a piece of banana or sweet juice in the bottom of a big bottle would collect a bunch of them, then I can put the cap on the bottle quickly and take them out. Buddhists can then release them, others can do what they want.

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