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Photo#1334707
Anza-Borrego station for Giant Red Velvet Mite - Dinothrombium

Anza-Borrego station for Giant Red Velvet Mite - Dinothrombium
Near Borrego Springs, San Diego County, California, USA
January 13, 2017
Size: ~10mm
[Note: Photos by Tom Chester; commentary by Aaron Schusteff]

The photos in this post are from my botanist friend, Tom Chester, who along with field companions Nancy Accola & Pat Matthews made this sighting during a botanical survey in the Borrego Desert. Details sandwiched by lines below are paraphrased from a portion of the remarks I received from Tom:
______________________________________________

At 1:23 p.m. the group noticed termites were swarming. Tom recalled termites often swarm right after a winter rain about midday...though here in the desert the swarm density was only about one tenth of what he'd experienced in the past around his home in coastal chaparral habitat of San Diego County. Then at 3:12 p.m. the group noticed a remarkably large, red, unfamiliar arthropod crawling with purpose on the ground. It was close to the size of a female velvet ant, perhaps a half-inch long, but looked arachnid-like. No one in the group had ever seen such a thing before.

Once home with reference resources available, members of the group settled on an ID of "giant red velvet mite" (genus Dinothrombium)...based on the excellent agreement in size, distinctive red velvety appearance, desert habitat, and emergence right after a rain with swarming termites...as described in the following passage from Evans(1)(2007):

"Giant red velvet mites appear in desert regions after summer rains. Their surface activity coincides with the nuptial flights of their prey, winged ants and termites. For most of the year they remain dormant in subterranean silk-lined chambers. Size to 3/8 inch (10 mm)"______________________________________________

This is the westernmost post of Dinothrombium on BugGuide to date. Currently, the only other CA post is from the Algodones Dunes, which are in far southeastern CA...not very distant from the Arizona border. There are only 2 species listed under Dinothrombium for our area in the catalog by Mąkol(2)(2000):

      Dinothrombium pandorae (Newell and Tevis, 1960).   Distribution: California
      Dinothrombium superbum (Banks, 1910).   Distribution: Arizona (originally described here)

Based on the distribution info above, the best candidate for Toms' find would seem to be Dinothrombium pandorae. Unfortunately, neither of the papers elaborating on that species are freely accessible on the web (i.e. Newell and Tevis (1960) and Tevis and Newell(1962)).

Another species of possible relevance here was originally described as Trombidium magnificum by LeConte in 1852; later referred to as Dinothrombium magnificum by Newell and Tevis in 1960; and listed as Phyllotrombidium magnificum in Mąkol(2)...but placed there under "Taxa incertae sedis". Mąkol(2) gives its distribution as "New Mexico, Texas"...but Art Evans used that name for a post from the Patagonia Mountains of Arizona (south of Tucson) that looks and sounds similar to Tom's Anza-Borrego find.

Some interesting details of the biology of Dinothrombium can be found on the associated BugGuide info page.

Images of this individual: tag all
Anza-Borrego station for Giant Red Velvet Mite - Dinothrombium Anza-Borrego Record for Giant Red Velvet Mite - Dinothrombium

There's a good discussion of this taxon in the Monroe's book
Tom mentioned that these giant mites are also discussed on pg. 654-655 of the excellent book(1) on insects & arthropods of the Anza-Borrego area written by BugGuide contributors by Lynn & Gene Monroe. So this sighting in the Anza-Borrego area by Tom's group is certainly not the first.

The Monroe's discussion is very interesting, with info on life history, habitat, ecological factors, behavior, and more. Among other things, they mention that in Mexico, these go by the common name of "angelitos" (little angels). They also speculate that the species here is possibly Dinothrombium pandorae, which was described from the relatively nearby Coachella Valley.

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