The explosion of life after a rain is amazing – winged forms of termites and ant swarm into the air with scissortails, nighthawks and kingbirds gorging themselves on the flight.
Dinothrombium pandorae , or" Rain bugs” or “Santa Claus bugs” also appear, tiny velvety red plush cutie-pies. Even though they are called “bugs”, they are not insects at all, but arachnids, related to spiders.
They’re the largest red mites in the world, all of 5mm long! They are distantly related to the pestiferous red mites of the garden and the tiny red water mites of the pond. Strictly diurnal, they don’t even like overcast skies. They emerge in great numbers about 9 a.m. on the first sunny morning after a rain, then in lesser numbers for a few mornings following. The rain has to be more than a third of an inch, and spring rains bring the most to the surface. As soon as they emerge, they begin wandering with purposeful, persistent, steady gait. An observer wonders if they are looking for food or mates. At first, when they meet they ignore each other, and it’s hard to see one eating anything. By noon all are hidden again. References state that the adults specialize in eating termites that have swarmed. But what is their life history?
They only emerge once a year. One researcher marked the burrows of hundreds. The most any did in succeeding rains was to come to the surface far enough to protrude their forelegs. They live in burrows, five to ten inches in depth and just wide enough for their tiny body. Even when the soil is baked dry, they remain turgid, full of moisture, bright in color. Termites swarm for less than an hour after a rain, either immediately or the following morning. As the “rain bugs” wander about, they come in contact with termites that have fallen to earth and in a few minutes eat enough to survive another year.
The researcher found eleven occurrences of mating behavior in four years. A male would stroke a female, dance with trembling steps and then spin a loose web two inches in diameter flat on the ground, enclosing a termite on which the female was feeding. No transfer of spermatophores was observed. Observers at the Sibley Nature Center discovered a different behavior from that of the published researcher, and photographed the males laying a string of silk in a circle then chasing the females around it, in a behavior that the staff named "circle-dancing."
After feeding and mating, the velvet mites dig new burrows, merely vertical shafts without branching tunnels. Sibley Nature Center volunteers photographed the mites binding the dirt together with more silk line, and then as they went underground, they pulled the silklines, and the hole was plugged. A conical mound of dirt marks the burrow until it dries and blows away. The insects move up and down in the burrow according to the season: 6 inches deep in the summer, an inch in the winter and halfway in fall and spring.
Eggs are laid in the burrow in clusters, almost three months after mating. After five weeks, the eggs hatch, then the “larvae” crawl to the surface to attach themselves to grasshoppers. But the researcher could not learn where they live on the grasshopper or when they return to the soil.
The study did not mention what predators feed on velvet mites. It’s possible that their red color is a warning of a foul taste and the only controls on their population are drought and the availability of food.
What fascinating little creatures!
Nature Notes is sponsored by the Dixon Water Foundation and is produced by KRTS Marfa Public Radio in cooperation with the Sibley Nature Center in Midland, Texas. This episode was written by Burr Williams of the Sibley Nature Center.