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Bug of the Week: Spider Mite Predators

In a previous post about hollyhock visitors, I mentioned the plants had spider mites. I wondered when the spider mite predators would show up. Turns out I didn’t have long to wait.

Spider mites are barely visible with the naked eye, and many of the beneficial insects and arachnids that feed on them are also incredibly tiny. In fact, I wished I had a microscope instead of a camera this week. Let’s take a “look.”

spider mite destroyer beetle

Those grayish black circles towards the top are lady beetles, but not the large orange and black ones like you might expect. These are called spider mite destroyers (Stethorus picipes). If you were not looking closely they might look like a bit of dirt or tiny seeds on the plant leaf. I can tell they are lady beetles by their rounded shape.

spider mite destroyer beetle pupa

The lady beetle larvae are on the plant feeding on the spider mites as well, as evidenced by the greyish pupa lying along the middle of the leaf.

You can see more of the life stages at the UC Davis IPM Online site.

red mite

A large red mite like this one might seem to be a bigger version of a problem mite, but it is actually a beneficial predator of spider mites. When you see single red mites that are readily visible and actively crawling about on leaves, that is probably a predatory mite feeding on plant mites or small insects. Mites have round bodies and eight legs.

minute pirate bug

Other point-sized predatory insects on the hollyhocks are minute pirate bugs (Orius tristicolor). (That is “minute” as in small, not the word for time.) The adults are black and white.

Minute pirate bugs feed on a number of small insects and mites. Here are some young pirate bugs or “nymphs” feeding within the webs of the spider mites. The nymphs are orange.

minute pirate bug nymphs

For a better look at the life stages, try this biological control page.

I didn’t get photos, but there were also some predatory thrips eating spider mites. Thrips are often thought of as plant pests, but some species are predatory.

It is great to see all the beneficial organisms having a banquet of spider mites. And I didn't have to do anything except watch the show.

4 thoughts on “Bug of the Week: Spider Mite Predators

  1. JimiD

    You will probably get some other predatory mites if the Stethorus don't clean the spider mites up first. The most common predators will be about the same size as the pest mites, but they will have much longer legs and more 'tear-drop' shaped bodies. Also they lay oval eggs, not spherical ones like the pest mites. If you find these oval eggs on the infested leaves, the predators have arrived and are working to control the pest mites.

  2. Suzy c

    I have dirt like insects which are eating my leaves on most of my plants on my small deck. Help tryed diluted dawn. Then added pepper. Will this work was afraid to spary to often? I have flower vegs. All are getting muched. on. what the bejeuis are they?

  3. Roberta

    Your problem could be any number of different insects or mites. See if you county has a Cooperative Extension office. Often they have Master Gardener volunteers or staff who would be willing to take a look at a sample of your plants and help you identify the culprit.

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