Moseying: Exploring the Natural World
After it rains, the rainbugs circle-dance in the morning sun
July 5, 2006
It rained! After seeing the landscape fade under clear skies and 11 days straight of 100 degree temperatures rain brings fresh vigor to humans, plants, and animals. Before the heaviest rain at 5 a.m on June 23rd, Deborah and I took a midnight walk. It was lightly sprinkling -- not enough to get us wet, but enough to soften our skin. Dry heat makes skin feel desiccated and rough. It was a fine walk, but was ended by a skunk spraying Lila the redbone ridgeback. We stuck her in the bathtub and scrubbed her down with Odor Destroyer and dish soap -- it was the best bath she ever had! (And not a hint of scent, afterward!)
At 9 a.m. on Sunday morning, June 25th, I took a walk across a pasture (and what I saw was happening in every pasture within 100 miles). The straw-colored grass had hearts of green -- our native grasses have the ability to green up within hours of a rain. The leaves do not completely die-- the cellular liquid becomes a gel and so what moisture is left can hardly escape through the cell walls. The grass endures, waiting for rain, and when it comes the gel liquefies and transpiration begins again before new growth. Within 48 hours a grass leaf blade can grow 2 inches.
Little piles of dark earthworm castings sprinkled the soil. Earthworms had been busy during the night. They, too, have to wait for rain for activity. During dry spells they wait, deep in the soil, encased in a shell made of their slime and the dirt. After a rain, they feast on the organic material decaying during the time of moistness, and void the processed material on the surface. As I knelt to photograph the castings, I noticed the black cryptogamic crusts had already lost the green of the algae within. The blue-green algae in cryptogams take nitrogen out of the air and transfer it to the soil -- and are the most important source of fertility in arid soils. Is there a relationship between the castings and cryptogams?
I also noticed a number of small holes with little cones of soil near the castings and cryptogamic crusts. Were these the exit holes for grassland termites? They swarm by the billions the morning after a rain. Or were they the exit hole for something else -- they looked fresher, as if something had come out earlier in the morning.
Taking a few more steps, I found the answer. The little cones were the exit holes for rain bugs -- plush red velvet mites. Some folks believe the rainbugs are baby tarantulas, but they are not. Some kids call them Santa Claus bugs because of their cute cuddly appearance. I found a rainbug with dirt on its back.
In May of 1996 when the rainbugs appeared I decided to find out if anyone had ever studied them. I found one research paper published in 1962 by the California Academy of Sciences and wrote a story for the Midland Naturalists' newsletter, "The Phalarope." Rainbugs eat grassland termites. After the sexually mature termites (alates) have flown, they come back to earth and mate. The females immediately dig back underground, but the males are "all used up" and are a major food source not only for the rainbugs, but also toads. Both the rainbugs and toads only eat once a year -- stuffing themselves on termites! The rainbugs
prefer to eat the termites on sunny mornings, but the toads are not as choosy. The rainbugs are usually back underground by noon.
Rainbugs live in 6-12 inch nonbranching tunnels in the soil that go straight down. Except during their emergence, the tunnels are closed except during succeeding rains, when the rainbugs remain at the burrow entrance. Keeping the burrows closed helps the rainbugs from drying out. They do not return to the burrow they left, but dig a new one. The little arachnids move up and down in the burrow according to the seasons the deepest during the summer, near the surface in the winter, and halfway down during spring and fall.
Since my original search for information in 1996, I have used some of it for programs at the Sibley Nature Center -- but I had forgotten two important parts of what I had found in 1996. I had forgotten that the rainbugs lay their eggs in clusters in the burrow a full three months after mating. After five weeks the eggs hatch, and then the newborn rainbugs crawl to the surface and attach themselves to grasshoppers. The research paper did not indicate how long the young rainbugs lived on grasshoppers, and if they injured the grasshoppers. I am going to be looking much closer at grasshoppers in October! Grasshoppers die with the first severe freeze, so the rainbug babies would return to the earth by then, for sure. I want to see a baby rainbug!
As I watched and photographed the rainbugs on June 25th, I noticed some fascinating behavior. At times 3-7 rainbugs would gather around one other rainbug and march around it in circles, and as they marched the circling rainbugs waved their front four legs. They moved their legs rapidly and continually, as they circled. After a minute or two, one of the circling rainbugs would dart to the one in the center and turn it on its back and then remain clasped to it for thirty seconds or so. I assumed the one in the center was a female, and that mating was occurring.
The research paper had reported that male rainbugs spun a loose web two inches of diameter flat on the ground, enclosing a termite upon which the female was feeding. The researcher assumed a spermatophore would be left on the webbing near the termite, but that behavior was not documented. I notice no webbing at all. (You can see for yourself in the photographs in the photoessay at www.sibleynaturecenter.org -- click on habitats, then click on prairie to mesquite brushland and click on rainbugs.) Do rainbugs on the Llano Estacado behave differently from California rainbugs? Are they even the same species?
Most invertebrates are poorly studied -- only the species injurious to man and his belongings have been studied thoroughly. Amateurs have increased our knowledge of the life history of butterflies and dragonflies far beyond that of academic researchers. My inquiries in 1996 were done before the rapid expansion of the Internet, so I checked online to research this article. I found dozens of pictures, and a few paragraphs about the critters, but no new information -- other than that one researcher was curious if the red coloration was a warning that it tasted bad -- and found it was very distasteful!
I found one website that had another scientific paper about the life history of rainbugs, but it was a subscription service, and the Sibley Nature Center can not afford its steep yearly fee of almost $1000. Oh, well, maybe someday it will be cost-effective!