Phytoseiulus persimilis
Predatory mite- Rate
- 2–50 /m² per release (Koppert); 100+ /m² on hot spots (Biobest)
- Temp
- 13–27 °C best (Koppert); Biobest 12–35 °C
- Best for
- Hot spots, humid air
Pest
Two-spotted spider mite
Tetranychus urticae
The short answer
A sap-feeding mite about 0.4–0.5 mm long, usually yellowish-green with two dark blotches, living in colonies under the leaves. Its feeding stipples leaves pale, then yellow or bronze, and heavy colonies spin webbing and strip plants. It thrives in hot, dry conditions — under glass, indoors and in summer heat outdoors.
hero macro · adult female and eggs on leaf underside
Adult female Tetranychus urticae with eggs and webbing, leaf underside. Photo: pending.
Identification
Adult females are about 0.4–0.5 mm long (the RHS says up to 1 mm) — moving specks to the naked eye, easy to see with a 10× lens. The body is oval and usually yellowish-green or amber, with a dark blotch on each side; the blotches are accumulated food, so a freshly moulted mite can lack them. Despite the British name glasshouse red spider mite, it is mostly green or yellowish, and turns orange-red chiefly when mated females go into their autumn and winter resting stage, or when a plant is too damaged to feed them.
Look on the underside of leaves, lower ones first: the mites, round translucent eggs, white cast skins and, as numbers rise, fine silk webbing. The webbing is what separates spider mites from aphids and thrips on the same leaves. The mites that move fast, look pear-shaped and orange-red with longer legs are predatory mites, not the pest — leave them be.
Easily confused with
- Predatory mitesBeneficial — leave itPredatory mites are pear-shaped, orange-red, longer-legged and fast-moving, and they lack the two dark spots of a spider mite.
- Tomato russet miteAlso a pestRusset mites are far smaller, about 1/5 mm, conical and yellowish-tan or pink; you need a 14× lens. Spider mites are rounder and larger, with two spots and webbing.
- Thrips and aphidsAlso a pestAphids and thrips also feed under leaves, but only spider mites spin silk webbing over the infested leaves.
Damage symptoms
Each feeding puncture empties a few leaf cells and leaves a pale fleck. A few mites are not worth acting on; UC IPM treats populations as damaging once they show visible leaf injury, especially on herbaceous plants. Water stress makes it worse. On squash and melons leaf loss can cut yield, and on beans and peas the mites attack the pods directly.
- Fine pale stippling on the upper leaf surface
- Leaves turning yellow, whitish or bronze, then dropping
- Mites, round eggs and white cast skins on the leaf underside
- Fine silk webbing over leaves, twigs and fruit in heavy infestations
- Petals browning and withering, like spray scorch
Lifecycle & degree days
Heat drives everything. UC IPM gives about 8 days from egg to adult at 28 °C against 28 days at 16 °C; the RHS gives 12 days at 21 °C and 55 at 10 °C. Generations overlap, so every stage is present at once. As days shorten, mated females turn orange-red and hide in cracks, canes, debris and leaf litter; in British glasshouses they re-emerge from late March, and breeding runs to October, though in a heated house damage can occur at other times too.
- Lower threshold
- 10–11.7 °C (two studies)
- Per generation
- 121–170 degree days °C, egg to egg
- Egg to adult
- About 8 days at 28 °C; 28 days at 16 °C
- Generations / yr
- Many, overlapping — no fixed count
- Female
- Lives 2–4 weeks
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Host crops
TomatoCucumberMelon & watermelonPepperStrawberryBeansBedding plantsHerbsHouseplantsMonstera & aroidsRosesGerbera & dahlia
UF/IFAS records this mite on more than 200 plant species (NC State says over 180), and the RHS says its range is so wide that few plants are completely immune — vegetables, fruit, ornamentals and houseplants alike. Weeds carry it between crops; NC State names violets, chickweed, pokeweed, wild mustard and blackberry as common sources. Each crop hub below carries the seasonal calendar for that setting.
Monitoring & action thresholds
Action threshold
No set count
UC IPM gives no number for gardens or greenhouse flowers: confirm live mites under a lens before treating, and release predators while numbers are low. The only numeric figure found is for strawberry — 5 or more mobile mites per leaflet in early spring (NC State).
Check leaf undersides at least weekly with a 10× lens, starting with the lower leaves and the hottest, driest spots in the house (UC IPM; UConn). Sticky cards are no use for this wingless pest. Tapping foliage over white paper shows the mites moving. Tag a few infested plants and recheck them to see whether predators are working — shrivelled, sucked-out mites are the sign — and scout infested areas last, because mites travel on clothing.
Beneficial
Biological control
Predatory mites are the main tool, and timing matters more than numbers: UC IPM reports the best results from releases that start early, while spider mites are still few, and its garden rule of thumb is one predator for every 10 spider mites. Phytoseiulus persimilis eats only spider mites and eats them fast, but it needs humid air — suppliers want relative humidity above 70%, UConn above 75% — and Koppert says it stops working above about 30 °C, although Biobest gives a wider 12–35 °C working range. Neoseiulus californicus is slower but copes better with heat and dry air and survives on other food, so it suits prevention; the two can be used together. The thrips predators Amblyseius swirskii and N. cucumeris may eat some spider mites, but UConn says they cannot be relied on, and Cornell says not to buy swirskii for spider mites because it cannot get through the webbing.
Neoseiulus californicus
Predatory mite- Rate
- 5–125 /m² per release by supplier; 100–200 /m² on hot spots
- Temp
- 13–35 °C best by source; active from about 8–10 °C
- Best for
- Prevention; warmer, drier spells
Amblyseius andersoni
Predatory mite- Rate
- 20–100 /m² (Biobest); 50–250 /m² weekly (Koppert)
- Temp
- Active 6–40 °C; best 20–28 °C
- Best for
- Low numbers; cooler conditions
Feltiella acarisuga
Spider mite predatory midge- Rate
- 0.25–25 /m² per release, at least 3 weekly releases (Koppert)
- Temp
- 68–81 °F (20–27 °C) best; humidity above 80% (Koppert), above 60% (UC IPM)
- Best for
- Hot spots in humid glasshouses, with persimilis
Stethorus punctillum
Spider mite destroyer- Rate
- 1 per 10 sq ft every two weeks (low) to 3–4 per 10 sq ft weekly (high), or 100–200 per hot spot (Arbico)
- Temp
- 67–90 °F (19–32 °C); 30–90% humidity (Arbico)
- Best for
- Established colonies; late-summer supply
Cultural controls
Dry air, dust and drought stress are what spider mites exploit, and broad-spectrum sprays are the other common trigger: UC IPM notes that insecticides kill the mites' natural enemies, that carbaryl, some organophosphates and some pyrethroids also favour the mites by raising leaf nitrogen, and that sprays in hot weather can set off outbreaks within a few days.
- Water well — drought-stressed plants take the worst damage
- Damp down paths and hose or mist leaf undersides; humidity helps but will not control mites alone
- Clear debris, old canes and weeds over winter, where resting females shelter
- Remove badly infested plants in late summer, before females go into winter rest
- Quarantine and inspect new plants before they join the others
Chemical, last resort
Broad-spectrum sprays often trigger spider mite outbreaksCheck any product before it goes on. Open the compatibility matrix →
- Insecticidal soapREI 12 h
- Horticultural oil (narrow-range)REI 4 h
- BifenazateREI 12 h
- BifenthrinREI 12 h
Rating: the effect on this pest's natural enemies if a spray hits them or they feed on treated plants. REI is the re-entry interval on farm and greenhouse labels; home labels usually give none, so follow the label.
Sources
UC IPM Pest Notes: Spider Mites, UC ANR Pub. 7405 (L.D. Godfrey; updated 12/2011)
UC IPM Floriculture & Nurseries Guidelines, Pub. 3392: Twospotted Spider Mites (updated 05/2010)
UC IPM, Relative Toxicities of Pesticides Used in Floriculture to Natural Enemies (updated 01/2022)
UC IPM Degree-Day Models: Twospotted Spider Mite (Carey & Bradley 1982; Herbert)
UF/IFAS EDIS EENY-150: Twospotted Spider Mite (T.R. Fasulo & H.A. Denmark, 2000)
NC State Extension: Twospotted Spider Mite (H. Burrack & J. Baker, 2013)
RHS Advice: Glasshouse red spider mite; Indoor plants: sap feeders (accessed Sept 2026)
K-State Research & Extension MF3665: Phytoseiulus persimilis (R.A. Cloyd, April 2024)
UConn Extension: Biological Control of Two-Spotted Spider Mites (L. Pundt, updated 2019)
Koppert: Spidex and Spical product pages; Biobest: Phytoseiulus-System (accessed Sept 2026)
Page status
Drafted from the sources below, then checked claim by claim against those sources on 23 September 2026.
Suggest a correction →Two-spotted spider mite by crop
The same pest behaves differently on different hosts. Each page below gives the host-specific control, rate and threshold.