University of Maryland Extension

Predatory Mites

Phytoseiid perdator mite
Phytoseiid predator mite

These tiny predators are not insects, but instead are members of the spider and tick clan (arachnids). They give cannibalism a good name, as they gobble up related spider mites by the dozens every day. Predatory mites look almost identical to and are about the same size as spider mites. You can tell predatory mites apart from spider mites by their shiny, unspotted, more pear-shaped body, and longer legs that enable them to move much faster than spider mites – but you’ll need magnification to see this! Predatory mites are widely used to control spider mites, and are commercially available.

Important species in Maryland: Phytoseiulus, Galendromus, and Neoseiulus spp.

Life stage(s) that feed on pests: Larvae, nymphs, and adults.

Insect(s) fed on: Predatory mites feed primarily on all life stages (eggs, nymphs, and adults) of a wide array of spider mites, as well as other plant-feeding mites such as rust mites and bulb mites. They also feed on the eggs and immature stages, such as crawlers and nymphs, of insects like thrips, whiteflies, and scale insects. The adults of some species feed on pollen, honeydew, fungi, and leaf sap.

Appearance:
Eggs: Minute, oblong, translucent white (versus spherical, colored or opaque pest mite eggs), laid singly on bottom sides of leaves along the vein.
Larvae/Nymphs: Larvae are tiny, oval, translucent shiny white to tan, with six legs; wingless. Nymphs look the same, but have 8 legs and are slightly larger than larvae, although smaller than adults.
Adults: Slightly larger than spider mites; pear-shaped; shiny translucent white but turning pale tan, orangey, reddish or green after feeding; eight legs; wingless.

Where to find: Eggs are laid on plants with spider mite infestations, on the leaf underside along the midrib. All stages are usually found on the leaf underside amid their spider mite prey. Adults look like moving specks and are more active than pest mites. To figure out which you have, gently blow on or touch them; if they quickly move away, they are more likely to be predatory mites.

How to attract and conserve: Avoid or reduce use of broad-spectrum insecticides, and use the least toxic materials for mite control. Horticultural oil can be applied prebloom to suppress pest mites early in the season with little impact on phytoseiid mites still in their protected overwintering sites. Establish naturalized areas bordering the garden to serve as a reservoir for predaceous mites that will colonize garden plants later. Predatory mites will disperse when they have eaten all available prey, so they must be reintroduced if spider mites reappear.


Contributors: Mike Raupp, Jon Traunfeld, and Chris Sargent

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