Fungus Gnats Love Your Houseplants

fungus gnat on round toothpick

Fungus gnat perched on a round toothpick


Fungus gnats are tiny flies that will take up residence in the soil of your houseplants.  Many people consider them to be pests, but they usually do little or no harm to mature healthy plants unless their larvae exist in large numbers.  From all I’ve read online, the adults do not feed and only live long enough to mate and lay eggs.  Actually, it’s our fault that they are attracted to our indoor plants.  Those of us who tend to over-water are setting out a banquet of delights for these innocent creatures in search of nurseries for their youngsters.

1 fungus gnat larva

The larva is smaller than a grain of rice

2 fungus gnat larvae

Fungus gnat larvae feed on a variety of decaying plant matter and fungi along with root hairs, leaf mold, algae and decomposing organic materials.  They seem to be especially drawn towards potting soil containing peat.  In large numbers they can be a serious problem in greenhouses because they can kill seedlings and young plants by chewing on their tender roots.  But, when they are living outside in my beautiful wildlife garden they aid in the decomposition of decaying plant matter.  One way to discourage the adults from laying eggs in your houseplants is to cover the soil with a half-inch or more of sterile sand so they can’t reach the soil.  Of course, the most important thing is to keep a healthy watering schedule for your plants – allowing the top inch or two of soil to dry out between each watering.

Fungus gnat pupa

Fungus gnat pupa


Fungus gnats have four stages in their life cycle – egg, larva, pupa and adult.  They undergo a complete metamorphosis like butterflies.  According to some sources, the adult gnats that live outside help to spread mushroom spores.

fungus gnats

I think it’s safe to say that the presence of fungus gnats indoors is a pretty good indicator that our plants may be in trouble – more from us than anything else.  And since I took all of these pictures from my own little infestation, it’s time for me to learn to be a better houseplant mommy!

Other articles you will enjoy:

Will We All Die If Honey Bees Disappear?

When Bugs Hug

Over-wintering Insects





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  1. says

    Hi! On potted (i.e., indoor) plants, a “tea” made from plain old tobacco will kill off the larval gnats. I purchase a pack of Camel cigarettes maybe every ten years or so and it comes in handy when needed. This late winter I’m having a bit of an experiment with a House (heirloom variety cherry-type) tomato that’s wintered over in a neighbor’s greenhouse. Spring began to threaten and sure enough there were the little crawly beggars making the top of the soil look like it was writhing! (Need I say my reaction was “Yuck!”?) I’ve applied about a cup of tea made from one-half a cigarette, and today will add another dose from two cups of ‘tea’ made from a whole cigarette. (The remainder I will save to apply in a few days when the next hatching comes around.) The experiment involved in this? Some tobacco may or may not carry a virus that isn’t good for tomatoes, so nicotine-containing products are usually non-recommended for application on tomatoes. Were it not for my neighbor’s other plants in the greenhouse (as well as my own, blooming, bird-of-paradise) I probably wouldn’t run the risk. But the tomato is growing and blooming and setting fruit, so . . . . we do what we have to do.

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