December 15, 2012

1 - Fungus gnats and flying aphids are the most likely small flying insects around houseplants in the winter.

Yard and Garden December 15, 2012


There are numerous small flying insects in the room where I keep my houseplants. What are these insects? What can I do about them? I do not want to use insecticides inside.

Victor M.


At this time of year there are several possibilities. One is the flying form of aphids, another is the adult phase of the fungus gnat. Many flying insects may be trapped by yellow, sticky traps available at many home and garden stores, or online. Place these traps in a bright window near the houseplants, some of the flying pests will be trapped. This will not catch all of the flying pests, but may be enough to reduce the problem sufficiently. It will also help you collect samples necessary for identification of the pest. Your local County Extension Service office can help you identify the pest and the appropriate treatment.

In the meantime, you can try identifying the pests yourself. Fungus gnats are small and very soft, so they are easily smashed. They are most common around the soil of potted plants, but they do fly away toward light sources at night or the window during the daytime. Fungus gnat larvae feed on the fungi in decomposing organic matter in potting soil and to some extent they feed on houseplant roots. They do relatively little harm to the plants, but are a nuisance.

The sticky traps will reduce the number of flying fungus gnats, but you may still want to use other control measures. There are some organic pest management products that may be used as a soil drench when watering your plants. These products will target the larval phase, preventing them from becoming adults and flying nuisances.

Do any of your plants have small insects on their stems or the undersides of their leaves? If so you probably have aphids and should treat them. Aphid can cause much more damage to plants than the fungus gnats. However, they are easily treated with insecticidal soap which is safe to use indoors on many plants. Read the label to be sure you can use it on your specific plants species. It can harm fabrics (upholstery, curtains, and carpets), so move the plants to the bathroom and spray the plants in the bathtub or shower or protect fabrics with plastic sheeting when spraying.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email:, office: 505-865-7340, ext. 113.


For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at, or at the Desert Blooms Facebook page.

Please copy your County Extension Agent and indicate your county of residence when you submit your question!