Field Notes
Phytoseiulus persimilis
The beneficial
Species
Phytoseiulus persimilis
Type
Predatory mite — an obligate specialist
Size
Slightly larger than a spider mite. Tear-drop shaped, bright orange to red, and very fast-moving
How it works
Moves rapidly across the leaves and navigates through spider mite webbing, which traps other predators — it walks into a web and works the colony from inside it
What it eats
Hunts
Two-spotted spider mite (Tetranychus urticae), all stages — eggs, nymphs and adults
Best against
Visible spider mite damage, webbing, or high pest counts — an active outbreak, not a clean plant
Won't touch
Anything that is not a spider mite. No pollen, no fungus, no debris, no alternative menu. It cannot survive without spider mites, so do not release it preventatively where there are no pests
What arrives
Format
Bottle of loose mites through a carrier that provides humidity and cushioning. Under good light you can sometimes see them moving against the pale grains. Everything in the bottle goes onto the plant
Where it works
Optimal temp
Active between 59°F and 86°F, ideally below 85°F — in extreme heat spider mites reproduce faster than Persimilis does
Humidity
60% relative humidity or higher, sustained. In drier air their eggs shrivel and fail to hatch. If your humidity fluctuates, use Californicus instead
Establishes
No. Once the spider mite population crashes the Persimilis population crashes shortly after, because it has run out of food — that is the design, not a defect. It will not linger on a clean plant, and if the mites return later you re-apply
Running it
Deploy
On arrival. There is no holding option for loose mites, and they cannot survive long in the packaging — do not hold them more than 24 hours, kept cool at 50–55°F and never frozen. Mist the plants lightly first, then rotate the bottle gently so the mites redistribute through the carrier
Placement
Onto infested foliage — hot spots first, clean plants never. Target the upper canopy and fresh growth where spider mites congregate, undersides included, because carrier dusted only on top surfaces mostly lands on the floor. Applying directly onto the webbing is encouraged
Replace
A single release is often enough for light to moderate pressure. For a heavier outbreak, a follow-up 7–10 days later, and a third only if live mites are still showing on new growth
Compatible with
Neoseiulus californicus — Persimilis onto the hot spots, Californicus across the rest of the crop as a patrol force that cleans up stragglers
Keep separate from
Sulfur — never in the same space. Heavy webbing too: take the bulk of it off with a strong stream of water or a vacuum before release, so the mites can reach the leaf surface where the eggs are
Chemical interval
Horticultural oil is done once it is dry. Neem is contact only. Insecticidal soap needs a day. Sulfur is 21 days. Rinse oils and soaps off thoroughly with water first — residues kill predatory mites as easily as they kill the pests
Safe around
Plants, humans and pets
