How long until the flies are gone?

Adult flies typically decline noticeably within 2–3 weeks of applying soil treatment and drop to near zero within 4–6 weeks.

Can I use Stratiolaelaps in leca or semi-hydro?

Sf Nematodes are the better choice for leca and true semi-hydro — they're applied as a drench and travel through the water column to reach larvae.

Will Stratiolaelaps harm my plants or earthworms?

No. Stratiolaelaps feeds on small arthropods and won't harm plant roots, earthworms, or beneficial soil microbes.

Do I need to treat every pot or just the infected ones?

Treat every pot in the space. Adult fungus gnats fly freely between plants and will lay eggs in any moist soil available.

Are fungus gnats actually harmful or just annoying?

The larvae are the problem. At high densities they feed on fine root hairs, reducing the plant's ability to uptake water and nutrients.

Fungus Gnat Treatment

The flies aren't the infestation.
Their larvae are.

Yellow sticky traps catch what's already flying. They don't touch the larvae chewing your roots. Biological soil treatment does.

Shop soil treatment → How to apply →

Not sure which pest you have?

Fungus gnats or thrips — easy to confuse.

You have fungus gnats if —

Small flies hovering around soil and draining to your pot saucers

Tiny black flies, 2–3mm, mosquito-shaped with long dangling legs
Flying around the soil surface — not on the leaves
Swarm when you disturb the pot or lift a leaf
Plants wilting or yellowing despite correct watering
Larvae visible in the top 5cm of soil if you look — white, 5mm, with a shiny black head
Worse after overwatering or in consistently moist media

You might have thrips if —

Damage on the leaves, not activity at the soil

Silver or papery streaks on the upper leaf surface
Tiny black fecal specks alongside the streaking
Scarred or twisted new growth
Tiny torpedo-shaped insects on leaves or in flowers — not flying around soil
No swarm when you disturb the pot

Go to thrips treatment →

Adult comparison

Adult fungus gnat — mosquito-shaped, long legs, 2–3mm

Adult thrips — torpedo-shaped, narrow, 1–2mm on leaves

Larval comparison

Fungus gnat larva — white body, black head, 5mm, in soil

Thrips larva — pale yellow, on leaf surface, ~1mm

No microscope needed — tell them apart in 30 seconds

You have fungus gnats if —

WHERE Flying around the soil and pot saucers, not the leaves

SHAPE Mosquito-like with long dangling legs — clearly a fly

SWARM Scatter when you disturb the pot or lift a leaf

LEAVES Look fine — no silvering, no streaking, no scarring

SOIL Dig 2cm down — white larvae with black heads visible

You have thrips if —

WHERE On the leaves and in flowers — not near the soil

SHAPE Tiny torpedo, barely visible — crawls more than flies

SWARM No swarm — individual insects on leaf surfaces

LEAVES Silver or papery streaking, black fecal dots, distorted new growth

SOIL Nothing unusual — the problem is above ground

Thrips leave evidence on the leaves. Gnats leave evidence at the soil. Check both and you'll know within a minute.

Go to thrips treatment →

What You're Dealing With

A soil pest wearing a flying disguise.

The adults you're seeing are the last stage of a soil-based lifecycle. By the time they're flying, they've already laid eggs. The larvae hatch in the top layer of your growing medium, feed on fine root hairs for 1–2 weeks, then pupate in the soil before emerging as the next wave of adults.

Killing the adults doesn't interrupt this. The next generation is already in your pots. The fix has to happen in the soil — which is exactly where biological controls operate.

Eggs laid in moist soil Female lays up to 200 eggs in the top 5cm of growing medium. Hatch in 3–6 days.

Larvae feed on roots The damage stage. Larvae chew fine root hairs for 1–2 weeks before pupating. This is when Stratiolaelaps and Dalotia hunt them.

Adults emerge and fly Live 7–10 days. Immediately lay eggs in moist soil and restart the cycle. These are what your sticky traps catch — not the problem, just the evidence.

Before You Buy Anything

Some infestations fix themselves with a watering change.

Fungus gnats need consistently moist soil to survive. Larvae desiccate quickly in dry conditions. If your infestation is early or light, adjusting your watering habits alone can collapse the population within a few weeks — no predators required.

What's making it worse

Overwatering The single biggest factor. Larvae need moist soil to move, feed, and survive. Keep the top 3–5cm of growing medium dry between waterings.

Peat-heavy or organic-rich mixes Fungus gnats feed on decaying organic matter as much as roots. Dense peat or coco-heavy mixes that stay wet are ideal larval habitat.

High ambient humidity with no airflow Slows evaporation and keeps the soil surface damp. Increase airflow at the canopy and pot level, especially in enclosed grow spaces.

New soil or recently repotted plants Bagged potting mixes are a common introduction point. Gnats and eggs are often already present in purchased soil — a good reason to treat preventatively when repotting into a new batch.

The free fix

Let the top layer dry out Wait until the top 3–5cm of soil is dry before watering again. Larvae in that zone die within a day or two. This alone will knock back a light infestation significantly within 2 weeks.

Bottom water where possible Watering from below keeps the top of the soil dry — exactly where gnat larvae concentrate. Roots still get water, the surface stays inhospitable.

Increase airflow at pot level A small fan directed at the soil surface speeds up evaporation and makes the top layer hostile to eggs and early-stage larvae.

Add a top dressing of sand or perlite A 1–2cm layer of coarse sand or perlite on the soil surface dries out fast and is difficult for females to lay eggs into. Cheap and surprisingly effective for light pressure.

If your infestation is light and you catch it early, drying out is often enough. If you're seeing consistent adult activity after two weeks of adjusted watering — or you have seedlings, cuttings, or young plants at risk — that's when biological treatment earns its place. The soil predators below work alongside drier conditions, not instead of them.

Soil treatment

Three organisms. One problem.

All three target fungus gnat larvae in the growing medium — where the infestation actually lives. Pick one or combine them based on your setup.

Traps alone don't stop it.

Yellow sticky traps are a genuinely useful monitoring tool — they tell you how bad the infestation is and whether your treatment is working. But as a standalone solution, they're not enough. The adults you're catching have already laid hundreds of eggs in your soil before you catch them.

The trap count tells you what's happening. Soil treatment is what changes it.

Fungus gnat larvae live in the top 5–8cm of moist soil, feeding on roots and organic matter. That's where the infestation lives. The adult flies are just the visible evidence of a soil problem. Until you address the soil, you can fill traps indefinitely and the population will keep rebuilding.

Run sticky traps alongside your biological controls — use them to track progress. When the weekly catch count drops to zero for two consecutive weeks, the soil reservoir is exhausted.

200

Eggs per female Laid directly into moist soil or growing medium. Hatch in 3–6 days depending on temperature.

5cm

Where larvae live The top layer of your growing medium — exactly where Stratiolaelaps hunts.

17d

Egg to adult at 75°F A new generation every 2–3 weeks in warm conditions. Trapping adults doesn't interrupt this cycle.

Application

How to run a fungus gnat program.

Simpler than thrips. One zone, one target, one decision.

Let the soil surface dry out first

Fungus gnats need consistently moist soil to thrive. Before releasing anything, let the top 2–3cm of your growing medium dry out between waterings. This alone will knock back the population — larvae in the surface layer die from desiccation. It also doesn't harm Stratiolaelaps, which lives slightly deeper.

Add yellow sticky traps — for monitoring, not treatment

Place traps at soil level, not above the plant. They won't solve the infestation but they give you a week-by-week count of adult activity so you can track whether your soil treatment is working. Expect the count to drop gradually over 3–4 weeks after applying your predators.

Apply Stratiolaelaps to the soil surface

Distribute the carrier material (vermiculite and peat mix containing the mites) evenly across your growing medium surface. Water in lightly to help them work into the top soil layer. Apply once — they establish and persist without re-releasing.

If using nematodes — apply as a drench every 2–4 weeks

Mix with room-temperature water (never hot — heat kills them) and apply to already-moistened soil. Nematodes are aquatic: they navigate the water film that exists between soil particles, not the particles themselves. Pre-moistening the media before you drench gives them a connected film to travel through from the moment of application. After drenching, keep the media moist for at least 48 hours so they can disperse through the substrate and reach larvae. If the media dries out too fast, they stall in place and effectiveness drops sharply. Nematodes don't establish permanently — re-apply on a schedule for the first 6–8 weeks.

Check environment — don't let media stay saturated

Review your watering schedule. Bottom watering helps — it keeps the top layer drier where gnat larvae concentrate while still hydrating roots. If you're in a high-humidity environment, increase airflow around the soil surface.

Hold the program until trap counts hit zero for two consecutive weeks

Sticky trap counts drop gradually — don't stop at the first quiet week. Pupae continue emerging for 1–2 weeks after the larval population is controlled. Two consecutive zero-catch weeks is the signal that the soil reservoir is exhausted. After that, maintain slightly drier soil surface conditions to prevent reinfestation.

Common Questions

Straightforward answers to straightforward questions.

8 Questions

Adult flies typically decline noticeably within 2–3 weeks of applying soil treatment. They'll drop to near zero within 4–6 weeks. The adults you see in week one and two are emerging from larvae that were already in the soil before you applied your predators — the treatment is working, it just takes a full lifecycle cycle to show up in the adult count.

If you're still seeing significant activity after 6 weeks, the most common cause is overwatering keeping the soil surface too moist for Stratiolaelaps to maintain population density near the surface.
Stratiolaelaps can navigate leca gaps but requires the media to stay slightly moist — they desiccate quickly in dry leca setups that drain completely between waterings. If your leca stays wet at the bottom and dries at the top, the mites will tend to retreat to the lower, moister zones rather than patrolling the full substrate.

Sf Nematodes are the better choice for leca and true semi-hydro — they're applied as a drench and travel through the water column to reach larvae wherever they are. Re-apply every 2–4 weeks since they don't establish permanently.
No. Stratiolaelaps feeds on small arthropods — fungus gnat larvae, thrips pupae, springtails, and similar soil-dwelling insects. They won't harm plant roots, earthworms, or beneficial soil microbes. They're also harmless to humans, pets, and birds.

Once the gnat population is controlled and their food source declines, the Stratiolaelaps population will naturally decline too. They don't become a persistent pest themselves.
The most common causes: overwatering keeping the soil surface too wet for Stratiolaelaps to thrive near the surface; applying a fungicide or soil drench shortly after release which can kill the predator population; or a new introduction of gnats from a recently purchased plant or bag of soil.

If you applied Stratiolaelaps more than 8 weeks ago and the population rebounded, a second application may be needed — particularly if you've recently repotted with fresh growing media.
Treat every pot in the space. Adult fungus gnats fly freely between plants and will lay eggs in any moist soil available — including pots that look unaffected. Treating only the visibly infested plants leaves reservoirs that will reinfest your treated pots within days.

If cost is a constraint, prioritize the largest pots with the most organic growing medium — these harbor the most larvae. But for reliable resolution, whole-space treatment is worth it.
Not concurrently. Both neem oil drenches and hydrogen peroxide soil applications will kill Stratiolaelaps and nematodes on contact. If you've used either recently, wait at least 2 weeks before introducing biological controls.

Yellow sticky traps are fine to run alongside biological treatment — they're physical, not chemical, and don't affect predator populations.
Yes — Stratiolaelaps is already part of the standard thrips soil program because it targets thrips pupae as well as gnat larvae. If you're dealing with both, a single Stratiolaelaps application covers the soil component of both infestations simultaneously.

You'll still need a separate foliar predator (Swirskii or Cucumeris) for the thrips larvae on your plants — Stratiolaelaps doesn't leave the soil. See the thrips treatment page for the full program.
Both, depending on population size. Adult gnats are mostly annoying — they don't bite and don't cause direct plant damage. The larvae are the problem. At high densities they feed on fine root hairs, reducing the plant's ability to uptake water and nutrients. Young plants, cuttings, and seedlings are most vulnerable — a heavy larval infestation can stunt or kill them. Established plants with healthy root systems usually tolerate low-level infestations, but populations grow quickly.

The practical answer: if you're seeing adults consistently, the larval population in your soil is already high enough to be worth treating.

Ready to treat

The soil is where this ends.

Stratiolaelaps is the fastest path to resolution for most growers. Apply once, it establishes, and it keeps hunting without re-releasing.

Shop Stratiolaelaps → Browse all fungus gnat treatments →

The flies aren't the infestation. Their larvae are.