Some mites have made an unexpected appearance amongst my house plants. I suspect they're predatory mites as they are relatively large and quite mobile. There's no sign of leaf damage or webbing typical of a spider mite infestation. If they are indeed predatory then they're most welcome to stay. However I don't see how they'll survive without the bad mites around. I have occasional outbreaks of those but they're quickly dealt with while in their early stages. One of these mystery mites was first spotted in a plant which I bought in the summer but I didn't think much of it at the time. This same plant became infested with spider mites in the autumn so it probably came with a mix of both types of mites. There was no sign of mites after several treatments with insecticidal soap. Then a large number of these mystery mites appeared in the pot sometime afterward but then disappeared just as quickly. Today they were seen in another pot some distance away but not in any other pots. (Are they going from one pot to the next in a group looking for prey?!) Has anyone had a similar experience? Any opinions?
I had never heard of predatory mites before so asked entomologist, Dr. Linda Gilkeson, who replied: There are soil dwelling predatory mites (native species) that eat a variety of small things found in soil as well as going up on leaves and eating thrips, mite eggs, etc. They could easily live in a pot plant without spider mites on the leaves or wander from pot to pot. I have attached a photo since sometimes what people think are ‘mites’ are actually springtails (collembola), thrips, etc. and don’t really have anything to do with pest mites on leaves. Besides seeing the predatory mite (Cucumeris sp.) in the photo Dr. Gilkeson attached, you can watch the thing in action:
Fascinating. They've moved on and are nowhere to be seen today. The mites that I've seen certainly fit the general description of predatory mites: The Good, the Bad and the Bugly (.pdf). Identity of the species is unlikely since these mites seem to lack readily identifiable features and because I lack the resources to look at them in great detail. I think their presence in my houseplant containers will be a blessing but I'll have to keep an eye on them. According to the document, Predatory Mite Pest Control – Using Predatory Mites In The Garden: I hope they don't turn out to be a problem. The following are a couple of videos from the same company, Koppert Biological Systems, on predatory mites that feed on spider mites:
An update: They're still here! One was spotted a few months ago and then another today. The predators must have managed to survive on what little food is available in the plant room and continued to breed. There has been plenty of pollen and nectar this year so they must be happy. Coincidentally there has not been any outbreaks of spider mites, knock on wood. Maybe these guys are dispatching the few that do make an appearance, before they have a chance to reproduce. As it turns out that one plant infested with mites was a mixed blessing.
Earlier I observed that these mites seemed to move from one container to the another as a group. It seems there may be some truth in that though it's difficult to imagine such minute creatures exhibiting social behaviour. The following article on Phytoseiulus persimilis mites supports this notion: Mites form friendly societies.
