True velvet mites are small, velvety, usually bright red mites often seen creeping around on rocks, planters, tree trunks, or on the ground, especially after a rain. They are harmless to people.
Like most other arachnids, the adults of true velvet mites have eight legs, which readily distinguishes them from insects, which have six legs. However, in their tiny, larval stage, velvet mites have six legs — but you will probably only see them attached to an insect or other arthropod.
Also, true velvet mites, like other mites, have only one obvious body section; the mouthparts look like they’re stuck onto the overall egg-shaped body. In contrast, insects have three body parts (head, thorax, and abdomen) and spiders have two (cephalothorax and abdomen).
True velvet mites are usually no bigger than about ⅛ inch long. But one group, the giant velvet mites (Dinothrombium spp.), may be nearly a half inch long. That genus is most common in the arid Southwest, but they can occur in eastern states as well.
Specialists examine tiny details of mouthparts and other anatomy to determine genera and species withing the family.
- Spider mites (family Tetranychidae) are common on plants, including houseplants. They suck juices from the foliage and spin tiny, wispy webs. They can be a nuisance on plants. Like true velvet mites, they are harmless to people. Spider mites are tinier than true velvet mites. When you squish them, they often make a red mark.
- Chiggers, also called harvest mites, are in yet a different family (Trombiculidae), and their larvae are parasitic on vertebrates (such as humans). You’re probably intimately familiar with chiggers. The larvae of true velvet mites, however, are parasitic on insects, spiders, and other small arthropods; true velvet mites do not harm people.
Adult length: typically to about ⅛ inch; varies by species. Some giant velvet mites (genus Dinothrombium) may reach nearly ½ inch in length.
Habitat and Conservation
To see the larval forms of true velvet mites, look for them clinging to their insect or arachnid hosts. They’ll look like tiny red eggs, usually stuck around legs, between body plates, or in other places where their host cannot wipe them off. At other times, true velvet mites typically live in the soil, among leaf litter, mosses, and other organic matter.
Certain species (especially the giant velvet mites, Dinothrombium spp.) are most common in dry, sandy soils (especially in the desert Southwest) and are usually only seen after heavy rains, when they come out in large numbers (hence the common name “rain bugs”); velvet mites in that group prey on termites, which also emerge from the soil after heavy rains.
Researchers sometimes estimate population densities of velvet mites by counting the numbers of larval mites per host. A number of fascinating studies have provided insights on how velvet mites locate and attach to their hosts; in some cases, it might be through sound, as male (chirping) crickets in one study were more likely to be parasitized than females.
As larvae, true velvet mites are external parasites that cling to and suck the juices of living insects or arachnids. As adults, they prey on the eggs of insects, or on insects. In many cases, the adults consume the eggs of whatever small insects they can find. Adults of genus Trombidium, however, apparently feed almost exclusively on the eggs of springtails (which technically are not insects).
True velvet mites do not parasitize people, or vertebrates, at any part in their life cycle. As larvae, some are very restricted to what types of insects or arachnids may serve as hosts or prey, while others have a broader menu. Researchers are teasing apart the complex parasite-host relationships; here are some of their findings:
- The larvae of giant velvet mites (Dinothrombium spp.) have been found parasitizing members of the grasshopper, beetle, and moth/butterfly insect orders, plus spiders and wind scorpions.
- The larvae of genus Allothrombium have been found parasitizing aphids, moths/butterflies, beetles, harvestmen, and other mites and ticks.
- The larvae of genus Trombidium have been found parasitizing members of the butterfly/moth, beetle, true fly, grasshopper, true bug, ant/bee/wasp insect orders, plus pseudoscorpions and harvestmen.
- The larvae of some velvet mite genera, however, are apparently limited to, say, aphids, or to spiders or butterflies/moths.
Not harmful to people. Potentially useful as beneficial biological control agents in agricultural settings.
True velvet mites, as a group, are undergoing taxonomic revision, so don’t be surprised if their names and apparent numbers of species and genera change in the coming years. Within subclass Acari (the mites and ticks), it’s becoming apparent that the two main groups (basically, the “mites” and the “ticks”), have separate evolutionary lineages. If that’s the case, then the long-standing group known as the Acari will be broken up, with the ticks more closely related to pseudoscorpions, and the mites more closely related to the camel spiders.
It’s complicated. True velvet mites and their relatives begin as eggs, which hatch into a form called a prelarva, which molts into successive larval, nymphal (protonymph, deutonymph, tritonymph), and adult forms. Several of these stages are inactive: the egg, the prelarva, the protonymph, and the tritonymph, the latter two being something like the pupae of insects. The stages that are active are the larval stage, where the mite is an external parasite on insects or arachnids, and the deutonymph and adult stages, which are free-living. The adults eat the eggs of insects, or insects. The adults mate and produce eggs for the next generation.
There is usually only one brood per year. In temperate regions such as in Missouri, adults usually lay eggs in the soil from midspring to midsummer, and these hatch after one or two months. These mites take their larval (parasitic) form in synch with the appearance and heyday of their hosts. If they are lucky enough to find and become attached to the correct kind of host, they’ll feed on it for one or two weeks, then detach from it and live for a while in the soil. The protonymph is a kind of resting and development stage, and then the deutonymph emerges in summer or fall. The deutonymph lives on the soil surface, feeding on plants, insect eggs, and other organic matter. The tritonymph is another resting and development stage, again occurring in the soil, and the adults emerge in the fall.
Depending on species and environmental conditions, the adults may lay eggs in the fall and/or hibernate in the soil over winter, laying eggs in the spring to midsummer. Some species may overwinter as nymphs.
True velvet mites perform interesting mating dances, moving in circles, tapping each other with their forelegs, and depositing threads to communicate with each other. The male deposits a spermatophore (packet of sperm) on the ground, and the female moves over to pick it up. Egg masses are deposited in the soil. The number of eggs varies by species and by size of female, ranging from dozens to tens of thousands.
Adult and deutonymph true velvet mites eat the eggs of insects, or entire small insects, including those of several crop pests. The parasitic larvae of true velvet mites can, in large enough numbers, diminish the survival and reproduction of problem insects such as lucerne (alfalfa) aphids, cotton aphids, black bean aphids, pea aphids, spider mites, and others. Thus some species of true velvet mites — especially those in genus Allothrombium — are being studied as possible biological control agents.
Considering that true velvet mites don’t harm people, yet parasitize or consume some problematic insects, it’s fair to consider velvet mites in the same “friendly” category as we usually view lady beetles.
The family name, Trombidiidae, is pronounced “trom-buh-dee-uh-dee.” Another name for this group is “trombidiids” (trom-buh-dee-ids). The “trom” is a Greek root referring to tremors or trembling, and in the Neo-Latin of this scientific name, “trombid” means “a little timid one.” On the scale of humans, these tiny, delicate creatures are indeed little timid ones — but as predators and parasites of other invertebrates, they seem less timid.
One species of true velvet mite is used in traditional medicine in Central India.
These interesting, humble animals are components of a healthy soil ecosystem. When people apply lawn pesticides that affect all arthropods, these are some of the nontarget, beneficial creatures that are destroyed.
True velvet mites are predators that serve as a check on the insects and other arthropods they feed on. They even sometimes eat each other. Meanwhile, few animals eat velvet mites, apparently because they are bad-tasting. The bright red color presumably serves as a warning to would-be predators.
True velvet mites spend much of their lives in soil, interacting with countless other soil organisms, so they are an important part of healthy soils, which means healthy plants, healthy animals, and healthy ecosystems.
How are true velvet mites related to other creatures you’re familiar with?
- The true velvet mites constitute just one of many families in subclass Acari (the mites and ticks), which in turn is just one of many groups in class Arachnida (a large group including spiders, scorpions, harvestmen, and more).
- Within the subclass Acari (the mites and ticks), there are two main divisions: superorder Parasitiformes, which includes the ticks we’re all too familiar with, and superorder Acariformes, which includes a bewildering variety of tiny mites, including the true velvet mites, spider mites (so common on houseplants), bee mites, chiggers (ugh!), the itch mites that cause scabies (ugh!), the ear mites that vex pets and other animals, a large group of plant eaters called gall mites, and a big group called the oribatids (also called armored mites, beetle mites, or moss mites), which are abundant and important members of healthy soil ecosystems.
- The true velvet mites and the chiggers are indeed in the same superorder (and even the same superfamily), but they are in separate families and are not closely related. The family names are confusingly similar, however: Trombidiidae for the true velvet mites, and the Trombiculidae for the chiggers.
- In case you’re wondering, lice are very unrelated to all of these; they are insects, not arachnids (the group that mites and ticks are in).