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Fungus Gnats Vs Drain Flies: Key Similarities & Differences That May Surprise You 110%

Gardeners are often confused between fungus gnats and drain flies because of their similar appearance and feeding habit, but they are very different pests.

Fungus gnats and drain flies are the same size (1-5 mm) but have different physical structures and colors, where fungus gnat has a mosquito-like pill shape, while the latter looks like a moth with fuzzy hairs.

In fact, they both thrive in moist soil conditions and feed on plant roots and bacteria, making it harder to separate the two.

Read on to discover the facts regarding fungus gnats and drain flies that may surprise you 110%. 

What are Fungus Gnats?

Did you know fungus gnats are the most prevalent garden pests that result in root rot in most plants?

Fungus gnats are tiny, delicate pests typically measuring 1.5-3 mm long with dark gray or black bodies and yellowish clear wings belonging to the family Sciaridae.

With their long, segmented antennae, they can quickly detect their environment and use slender wings to take flight.

fungus gnats
They are mostly common in autumn and spring and are active during the evening, making them hard to notice.

Preferred Habitats of Fungus Gnats

Remember, they prefer moist and decaying surroundings and thrive in soggy soil conditions, where they suck up flowers and lay eggs in the soil.

Overwatered plants with ample moisture and decaying organic matter provide an ideal habitat for their larvae and adults.

  • Potted Plants: Overwatered containers with damp soil are attractive breeding grounds for gnats.
  • Compost Bins: They thrive in compost piles where organic material decomposes and creates a humid environment.
  • Wet, Organic Matter: Rotting fruits, fallen leaves, and garden decaying vegetation may invite fungus gnats.

What are Drain Flies?

Drain flies, also known as sink, filter, or sewer gnats, are tiny, flying pests belonging to the family Psychodidae.

Ranging between 1.5-5 mm long, drain flies boast a humpbacked appearance with a fuzzy, moth-like structure.

drain flies
Unlike fungus gnats, drain flies display broad, hairy wings and is usually found in gray or light brown shade.

Preferred Habitats of Drain Flies

Like fungus gnats, they are attracted to moist places, such as constantly wet houseplants, where their larvae thrive.

However, they are more prevalent in and around the kitchen.

  • Drains and Sewages: They frequent clogged or dirty drains, sewage pipes, and septic tanks; hence the name ‘drain flies.’
  • Standing Water: Stagnant water sources, waterlogged soil, and moist compost piles provide breeding grounds for drain flies.
  • Wet Organic Matter: Sometimes, they infest areas with decaying vegetation, organic debris, and decomposing material.

Similarities Between Fungus Gnats and Drain Flies

As previously mentioned, gardeners may confuse fungus gnats with drain flies because of their similar appearance.

Here are a few similarities that you will find in these pests.

  1. Appearance and Identification: Fungus gnats and drain flies are tiny insects, typically measuring 1 to 5 mm long. They both possess wings, enabling them to take flight and infest different areas.
  2. Behavior and Attraction: Both pests are primarily active during the evening and nighttime, more noticeable in low-light conditions.
  3. Environmental Preferences: They are drawn to areas with high moisture, such as damp soil, standing water, and decaying organic matter.
  4. Harm to Houseplants: Fungus gnat and drain flies larvae feed on organic materials in the soil, affecting the plant root’s health and vigor.

Differences Between Fungus Gnats and Drain Flies

Here is a table highlighting stark dissimilarities between fungus gnats and drain flies.

AspectFungus GnatsDrain Flies
SizeSmaller than drain flies with delicate, slender bodies and long wings.Small, humpbacked insects with fuzzy bodies and hairy wings.
Preferred HabitatsDamp soil, overwatered plants, organic matter with fungal growth.Standing water, sewage systems, drains, and decaying kitchen waste.
Larval Feeding BehaviorFeed on fungal hyphae and organic debris in the soil, causing and increasing root damage.Feed on decaying organic matter in drains and sewage, with limited direct impact on plant roots.
Plant DamageStunt plant growth due to root damage, and reduce overall plant vigor.Indirectly affect plant roots by disrupting soil nutrient and affect plant's vigor.
Impact on Plant HealthWeakens plants and makes them susceptible to other stresses and diseases.Weaken plants only from heavy larvae infestations in the soil.
Attraction to PlantsAttracted to damp soil and overwatered plants.Not directly attracted to plants, but may appear due to rising moisture level or decaying organic matter.

How to Get Rid of Fungus Gnats and Drain Flies?

Overall, both pests pose problems to houseplants, affecting their growth and vigor.

It is important to fix the fundamental causes of infestation to help mitigate the damages caused by fungus gnats and drain flies.

  • Discard the plant with severe root rot or visible damage, as they will likely transfer pests to nearby plants.
  • Allow plant soil to dry out before watering again to discourage fungus gnat larvae from thriving.
  • Inspect the root for rot, remove the affected roots, and transplant in a fresh potting mix.

  • Overwatering creates an ideal environment for fungus gnats—water plants only when the 1- inch top soil is dry.
  • Ensure well-draining soil and plant containers have enough drainage holes to keep water from sitting in the soil.
  • If possible, replace the top layer of soil with a fresh, sterile potting mix to remove pest eggs and larvae.
  • Place yellow sticky traps near the plants during spring and summer to catch adult fungus gnats and flies.
  • Regularly clean and disinfect drains, pipes, and sewage systems to remove organic matter. Apply drain cleaners or use boiling water to eliminate breeding sites.

Use copper-based fungicide and insecticides only when the pest infestation is rampant with significant damage done to many plants.

From Editorial Board


When it comes to houseplants, fungus gnats can do more severe damage to them than drain flies.

However, the extent of the damage will vary depending on the severity of the infestation.

As a preventive measure, avoid overwatering your plants and keep the area moist and debris free with better air circulation.