Fungus Gnats - (Sciarids) - Sticky Trap Guide

Fungus gnats (Sciarid flies) are tiny, dark-coloured flying insects that thrive in damp soil conditions—especially in greenhouses, houseplants, seed trays, and compost-rich beds. While the adult gnats are mostly a nuisance, it’s their larvae, dwelling in moist compost or growing media, that cause real damage. These larvae feed on delicate plant roots, often leading to poor plant health, stunted growth, and even plant death in severe cases.

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How to Identify Fungus Gnat Problems

Tiny black flies hovering near soil surface, particularly after watering

Yellowing or wilting leaves on seedlings or cuttings

Stunted growth or damping-off in young plants

Visible larvae in the topsoil (thin, translucent with black heads)

Fungus gnats are most common in warm, humid environments, making them a frequent problem in UK greenhouses, indoor grow tents, and propagation setups.

How Sticky Traps Help with Fungus Gnats

Sticky traps are one of the most effective early warning tools for fungus gnats. Adults are attracted to yellow sticky traps, which mimic flowers, and once they land, they’re trapped on the non-drying adhesive surface. This helps:

Monitor gnat populations

Interrupt the breeding cycle

Guide further treatment decisions

For best results, place yellow sticky traps horizontally near the base of your plants—right above the soil where adults emerge. Combine with good watering practices and, if needed, biological controls like Steinernema feltiae nematodes.

Fungus Gnat Control: Best Practices

Let soil dry between watering to disrupt larvae development

Bottom-water instead of overhead watering to reduce surface moisture

Use biological controls like nematodes or predatory mites for larvae

Combine sticky traps with these methods for best results

Sticky traps won't eliminate larvae in the soil, but they are essential for monitoring, reducing adult populations, and preventing breeding.

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FAQ - Pest Name

What attracts fungus gnats?

Fungus gnats are drawn to moist, organic-rich soils—especially in overwatered pots or seed trays. They also respond strongly to yellow colours, making yellow sticky traps highly effective for catching adults.

Are sticky traps enough to get rid of fungus gnats?

No. Sticky traps help monitor and catch adult gnats, reducing breeding, but you’ll still need to manage moisture levels and target larvae in the soil for full control.

Can fungus gnats harm plants?

Yes. While adults don’t feed on plants, the larvae can damage roots, especially in seedlings and cuttings, leading to stunted growth, poor uptake of nutrients, and even plant loss.

Where should I place sticky traps for fungus gnats?

Place traps horizontally, just above the soil, especially in propagation trays, pots, or beds where fungus gnats are active. Reposition as plants grow.

Are sticky traps safe to use indoors?

Yes. Insect-specific sticky traps (like those sold on StickyTraps.co.uk) are non-toxic, odour-free, and safe to use around children and pets—just avoid placing them near beneficial insect release sites if you're using biocontrols.

An Ode to Gnats

Oh fungus gnat, thou wingèd pest,
Thou art the uninvited guest.
You rise from soil with buzzing grace,
To fly directly in my face.

You haunt my leaves, my seedling trays,
You thrive in damp, neglected bays.
With larvae vile, you chew and gnaw,
A rootless plant? Your final straw.

No epic wings, no noble sting,
Just errant zigzags in a ring.
You mock my houseplant’s sunny spot,
And lay your eggs where things go rot.

But lo! A trap of yellow hue,
Your downfall, sticky, strong, and true.
You spot it, swoon — a golden sun!
And soon your gnatty days are done.

So rest now, friend — your time has passed.
You flew too close, you stuck too fast.
From compost crypts to skies you soared…
Now glued to glory. Trapped. Ignored.