Rain Bugs

One of the beautiful animals that make an appearance during our summer rainy season is the red velvet mite, Dinothrombium spp. These very large mites spend most of the year under ground. Mites are arachnids in the order Acari, along with the ticks. There are over 30,000 species of mites, and perhaps thousands more to be discovered. Mites have many lifestyles: some are parasitic, some are scavengers, some are predators and still others are herbivores. The velvet mite is the giant among mites, with some species approaching ½ inch in length. Most mites are tiny, even microscopic.

The red velvet mite’s emergence during the rainy season coincides with the presence of large numbers of winged ants and termites, upon which the mites feed. Red velvet mites are subject to desiccation and individuals in some genera have waxy coatings to reduce water loss. Red velvet mites can be present in large numbers. An entomologist flying into Tucson noticed that the desert near Picacho Peak had a red appearance. When he went back to investigate he found that the color was due to the presence of red velvet
mites.

Some individuals are covered almost entirely with red hairs, while others have both red and white hairs. Entomologist, Carl Olson, sent specimens of both color phases to mite experts at Ohio State University. These experts told Carl that the different colored mites were probably the same species, just a variation in the color pattern. Carl said he thinks the species we have in our area is D. magnificum.

Red velvet mites have few natural enemies, most likely because of their distastefulness and the red warning color. One source found that when Dinothrombium spp. was offered as prey to many species of arthropod-eating animals, they were rejected by most and spit out by ones that tried to eat them. Another source said that when the velvet mites were placed on an ant hill, the ants avoided them.

velvet mite_Photo by Patti Gardiner
Red velvet mite. Photo: Patti Gardiner

These mites have a rather complex life cycle, with pre-larval and larval stages, three nymphal stages (protonymph, deutonymph, and tritonymph) and then adult males and females. The prelarvae, protonymphs, and tritonymphs are calyptostatic, meaning that they are inactive. The larvae are ectoparasitic on other arthropods. Red velvet mite larvae in the genus Dinothrombium have been found on insects in the order Orthroptera (grasshoppers), Coleoptera (beetles), Lepidoptera (moths and butterflies), and on spiders and sun spiders. The deutonymphs and adults are free-living predators of winged termites and ants.

Complex mating behaviors have been described for a few species of these beautiful arachnids. The male and female mites do encircling dances, during which pair-dance signaling threads are deposited. In at least one species, the dancing pair tap each other with their first pair of legs. Sperm transfer is indirect, with the male depositing a spermatophore that is then picked up by the female. One account I found says that the male deposits his sperm (spermatophore) on elevated surfaces such as twigs or stalks. One author of this account describes these areas as “love gardens,” and the second author describes this array as “tiny golf balls on tees.” The male will deposit an intricate trail of silk leading to the sperm. The female lays her eggs in masses in the soil or sand. The number of eggs laid varies with the species. One species of Dinothrombium (D. tinctorium) lays 100,000 eggs.

Other fun facts? 

  • A large red velvet mite that occurs in India, Dinothrombium grandissimum, is sold in bazaars there. The red oil of this mite is used to treat paralysis and is referred to as “Indian Viagra.”
  • Studies have also shown that substances in this mite have antifungal and antibacterial properties.

Written by Buzz Hoffman, ASDM Friday Docent

References:
Olson, Carl. 2013. Personal Communication, July 24, 2013.
Rotenberk, Lori. 2004. Chicago Wilderness
http://www.chicagowilderness.org/CW_Archives/issues/fall2004/mite.html
University of Wisconsin-Milwaukee Field Station
http://www4.uwm.edu/fieldstation/naturalhistory/bugoftheweek/red_velvet_mite.cfm
Werner, Floyd and Carl Olson. 1994. Learning about and Living with Insects of the Southwest.
Fisher Books, 162 pp.
Wikipedia. http://en.wikipedia.org/wiki/Trombidiidae
Zhang, Zhi-Quing. 1998. Biology and ecology of trombidiid mites (Acari: Trombidioidea).
Experimental and Applied Acarology, 22: 139-155.


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