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How to identify it
- Larvae are slow-moving, maggotlike and no more than about 1/12 inch (2 millimeters) long, tapering toward the head. Young larvae are yellow; older ones take on the color of what they have eaten, from brown or gray to orange, red, yellow or white. Look for them among spider mites and their webbing.[1]
- Adults are delicate flies with long, slender legs and antennae, 1/25 to 1/12 inch (1 to 2 millimeters) long, grayish, light brown, orangish or pink. At rest they hold the wings up, angled and apart, with the antennae curled back over the body.[1]
- Pupae are in flat, round, whitish cocoons about 1/12 inch across, often next to a leaf vein among the mite webbing and empty mite skins.[1]
- Eggs are tiny (about 0.3 millimeter), oblong and yellowish, laid singly among the mites, often on the undersides of leaves near the webbing.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Fungus gnats | Adult fungus gnats look similar but have a distinct Y-shaped fork in the wing vein near the wing tip; mite midges have only a faint fork toward the rear part of the wing. Both can turn up together in greenhouses and on container plants.[1] |
| Dustywings | Dustywing cocoons are also flat and round, but mite midge cocoons are a third of the size or smaller and occur only in mite colonies; dustywing cocoons are somewhat oblong and may be on bark or foliage.[1] |
| Aphid midge | A related predatory gall midge that eats aphids rather than spider mites.[1] |
Where it lives
Feltiella acarisuga has a cosmopolitan distribution. In California at least three Feltiella species occur, mostly in coastal areas and greenhouses, on crops such as artichoke, avocado, citrus and strawberry and on mite-infested garden and landscape plants.[4][1]
Biology and life cycle
The larvae suck out the contents of their prey and prefer mite eggs and young mites. Each larva eats up to several dozen mite eggs a day and about 200 to 300 eggs over the 1 to 2 weeks it feeds before pupating.[1][2]
In a laboratory study at about 80 degrees F, development from egg to adult took about 17 days, adults lived about 13 days, and each female laid about 33 eggs. UC IPM gives egg-to-adult times of about 2 weeks in warm weather to 5 weeks in cool weather.[2][1]
There are several generations a year. Females stop laying eggs when days are short, and the insect spends the winter as a mature larva in its cocoon; in greenhouses with supplemental lighting they can keep breeding all year if mites are present.[1]
They do best at 68 to 81 degrees F with relative humidity above 60 percent. Long dry spells cut egg laying and survival, so they can be uncommon in low humidity.[1]
Damage and signs
- Mite midges do not damage plants. They feed almost exclusively on spider mite eggs, immatures and adults.[1]
Health risk
Mite midges are predators of spider mites; UC IPM lists them as natural enemies and describes no harm to people.[1]
Control
Prevention
Mite midges are beneficial and need no control. To protect them, avoid broad-spectrum and persistent insecticides and miticides, and grow flowering plants that supply nectar and pollen for the adults.[1]
Biological control
They are sold for release against spider mites in commercial greenhouses and nurseries, usually as weekly releases for at least four weeks in infested spots. In a laboratory comparison a larva ate up to 50 twospotted spider mite eggs a day, more than either of two predatory mites tested, but because they multiply more slowly than spider mites, frequent releases may be needed.[1][3][2]
Common questions
- What are the tiny orange maggots in the spider mite webbing on my plants?
- They may be mite midge larvae, predators that feed on spider mites and their eggs. Leave them alone; they help control the mites.[1]
- Can I buy mite midges to control spider mites?
- Yes. Feltiella acarisuga is produced commercially and released against spider mites, mainly in greenhouses and nurseries. It works best where humidity is fairly high.[1][4]
Sources
- University of California Statewide IPM Program, “Mite Midges (Natural Enemies Gallery).” ipm.ucanr.edu/natural-enemies/mite-midges/ (accessed 2026-11-09)
- Environmental Entomology (via NCBI PubMed), “Predation and life table of Feltiella acarisuga preying on eggs of Tetranychus urticae (Environmental Entomology 36(2), 2007; abstract).” pubmed.ncbi.nlm.nih.gov/17445371/ (accessed 2026-11-09)
- Journal of Insect Science (via NCBI PubMed), “Functional responses and prey-stage preferences of a predatory gall midge and two predacious mites with twospotted spider mites (Y. Xiao et al.; Journal of Insect Science 13:8, 2013; abstract).” pubmed.ncbi.nlm.nih.gov/23879370/ (accessed 2026-11-09)
- Insects (MDPI), via NCBI PubMed, “Effect of Temperature on the Development and Survival of Feltiella acarisuga Preying on Tetranychus urticae (Insects 12(6):508, 2021; abstract).” pubmed.ncbi.nlm.nih.gov/34072985/ (accessed 2026-11-09)
- iNaturalist, “Feltiella acarisuga taxon page (order and family).” www.inaturalist.org/taxa/967252 (accessed 2026-11-09)