Soil predatory mites
Also known as Stratiolaelaps scimitus, Hypoaspis miles, Gaeolaelaps aculeifer, Hypoaspis aculeifer
In short
Several tiny mites that live in the top layer of the mix are predators of fungus gnat larvae, thrips pupae and other soil pests. Stratiolaelaps scimitus (sold under its old name Hypoaspis miles) is widely produced for greenhouses and houseplants and works best as a preventive or early release.
How it looks
About 0.5–1 mm long, light brown to tan, with eight legs as adults. They move quickly over and just under the surface of damp potting mix, hunting mostly in the top 1–2 cm. Eggs are oval; six-legged larvae hatch and become eight-legged nymphs, then adults.
Signs
No plant damage. Small, fast, pale brown mites on the mix surface, often alongside a falling number of fungus gnats.
Life cycle
Females lay up to three eggs a day; eggs hatch in one to three days, and development from egg to adult takes about 10–34 days depending on temperature.
What favours it
Moist but not waterlogged mix; they cannot survive in standing water. They need a minimum of about 15 °C. When prey is scarce they can live on algae and decaying plant material, which lets them persist in pots.
Prevention
- Buy from a reputable biological control supplier and release on arrival.
- Avoid soil drenches of broad-spectrum insecticides after release.
Treatment
Start with the first step and move down only if the problem persists.
- Sprinkle the carrier material onto the mix surface of infested or at-risk pots, following the supplier's rate.
- Release early, while fungus gnat numbers are still low.
Pros and cons
Pros
- Eat fungus gnat eggs, larvae and pupae, thrips pupae, springtails and other small soil animals.
- Can persist in pots on alternative food.
- Harmless to plants, people and pets.
Cons
- Work slowly and are less effective against an established heavy infestation.
- Need a live product, correct storage and prompt release.
- Also eat harmless springtails.
Look-alikes
- Spider mites
- Plant-feeding mites that live on leaves and make fine webbing, not in the mix.
- Bulb mites
- Slow, pale, rounded mites clustered on damaged bulbs, corms and roots.
- Springtails
- Six-legged, jump when disturbed.
Where you find it
Used in potted plants, bedding plants, poinsettias, propagation benches and houseplants; also used by reptile keepers against mites.
Related
Sources
Written in our own words from these sources. Check a product label before using any treatment.