Are Velvet Mites Harmful to Plants?

Red velvet mites, members of the Trombodiidae family, are some of the largest and most conspicuous members of the arthropods classified as mites. Relatives of spiders, adult mites have eight legs and there are thousands of kinds. Most mites are so small you never notice them and need a microscope to see them well. Not so the velvet mites, which are about 1/3 inch long. They live in soil, sand and litter and do not harm plants in any way.

Look for adult velvet mites after a winter or spring rain. The giant red velvet mites (Dinothrombium pandorae) emerge from burrows in the sand for a few hours after the rain. Their emergence coincides with the winged flight of their prey: termites. After mating, the termites fall and detach their wings. The giant velvet mites pierce the termites with their sucking-piercing mouth parts. Adult mites are only seen for a few hours every year. After feeding and mating, they burrow back into the sand. Other kinds of velvet mite feed on a variety of insects and insect eggs. Most velvet mites spend most of their lives in soil, humus, moss or sand, emerging to find hosts, prey or mates.

The best chance you have of seeing immature velvet mites is to look on the bodies of other insects. One of the immature forms, the larva, is an external parasite on insects, including grasshoppers, aphids, butterflies, beetles, true bugs, flies, bees and wasps. They also parasitize spiders and harvestmen, scorpions, millipedes and centipedes. They often feed on insects that damage plants and may be candidates as biological control agents. The immature mites wait on vegetation and jump onto passing host insects or other arthropods, attaching themselves to the host's body with their sharp mouth parts and sucking the host's blood. The bright red young mites are quite noticeable against the darker body colors of their hosts.

After feeding and mating, female velvet mites burrow back into the soil and lay from 60 to 100,000 eggs, depending on the species. The eggs hatch into a pre-larvae, which don't move or feed. They turn into larval mites with six legs, and these parasitize host insects for one or two weeks. They drop off, enter the soil, and change into quiescent protonymphs. Active deuteronymphs hatch from these in the summer or fall and are free-living predators. Re-entering the soil, another resting form, the tritonymph, develops. The adults usually emerge from the tritonymph in fall and hibernate in the soil over winter.

Male and female mites perform a mating dance, encircling and tapping each other on the back with their front legs. The male deposits a sperm sac on the ground and the female picks it up. The larvae depend upon the host movements to disperse them. Some larval velvet mites have modified third legs for jumping, and can jump a distance of 25 times the length of their bodies.