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All About Stratiolaelaps scimitus (Hypoaspis miles) Predatory Mites

Information about predatory mites for the mushroom industry to manage mushroom phorid flies.

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Updated:

March 18, 2026

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Predatory mite

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What are predatory mites (Stratiolaelaps scimitus)?

S. scimitus (or H. miles) predatory mites are beneficial biocontrol agents. They are small (see Figure 1 for scale), predatory arthropods that live in the soil and feed on many other arthropods. These mites have been commercially available for several decades and are used to kill fungus gnat larvae and other agricultural pests. S. scimitus mites are expected to live over 70 days and take between 10 and 34 days to go from egg to adult, depending on compost temperatures. Adult mites can lay 3 eggs every 2 days.

Size of a mite in comparison to a penny — Figure 1. Predatory mite size scaled with a mold mite and an American penny.

Do S. scimitus predatory mites kill mushroom flies in compost?

Yes. S. scimitus mites are non-visual predators that are believed to primarily use vibration signals to locate and capture prey. Laboratory studies by the Penn State Mushroom Fly Research Team showed that one predatory mite can kill more than 11 fly larvae in 3 days! (Figure 2). In more recent trials on farms, growing rooms treated with predatory mites had 40% lower phorid fly emergence compared to untreated rooms. Growers applied 8 L (approximately 200,000 mites) at spawning, followed by a second application the day before casing.

Two photos showing predatory mites feeding on mushroom fly larvae — Figure 2. Predatory mites feeding on dead mushroom fly larvae

Graph showing the reduction of phorid flies with introduction of mites — Figure 3. Results from field studies. Growing rooms were paired with the number of flies caught on monitoring traps in one Treatment Room (received mite applications) compared to one Control Room (no predatory mite applications). There were 10 room pairs in this study. Positive bars indicate the emergence in mite-treated rooms was lower than the emergence in rooms that did not receive mites.

Do S. scimitus predatory mites pose a threat to my crop?

The Penn State Mushroom Fly Research Team has done extensive studies that found S. scimitus do not damage the growing mushroom mycelia. Studies also found that the presence or absence of mites did not change the amount of new dry bubble (L. fungicola) colonies that grew in laboratory studies. Studies are ongoing to evaluate S. scimitus transmission of green mold (T. aggressivum).

These mites live underground. While they can’t "see", they can differentiate between light and dark and are strongly repelled by light. These mites should not accumulate on the mushrooms or interfere with picking, as they prefer to be hunting in the compost.

Unlike flies, mites are more likely to be contained to the growing room where they are applied because they cannot fly. Most mites will be steamed off in the compost at the end of the growing cycle. If a mite makes it out of a growing room, it will likely burrow into the soil and continue hunting for other arthropods.

How should I apply S. scimitus predatory mites to control mushroom flies?

The Penn State Mushroom Fly Research Team is testing two different application methods. Mites are either mixed with the supplement into phase III compost during compost production or hand-applied on beds of phase I or phase II compost. Mites that were mixed within the compost lived for at least 45 days in the mushroom compost. Studies are inconclusive as to which application method is better. If hand-applying, sprinkle mite media down each bed. Mite media does not need to be distributed evenly across each bed, but avoid pouring the media out in a pile. The mites are robust and can survive being turned and mixed with supplement and compost. Studies showed that mites mixed in with supplement survived for 45+ days in mushroom compost on farms.

Do S. scimitus predatory mites kill Sciarid flies?

Studies are ongoing to determine S. scimitus efficacy against sciarid flies. There is literature to suggest efficacy, but early results from the Mushroom Fly Research Team have been inconclusive thus far.

How should S. scimitus be stored?

S. scimitus mites are predators and should be used within the week they are received as predators in close proximity will kill each other. They can be stored at room temperature.