Essays

Wild On The Prairie: Invertebrates

Springtails are rarely found on the Llano Estacado
March 17, 2002

On a cold winter's morning after a drizzly rain overnight, in a shallow pool of water full of decaying leaves, the water's surface was poxed with what appeared to be black dust, like iron filings gathered by magnets. Puzzled, I checked the other bird baths, ponds, and water tanks of the Gone Native Arboretum. Only one other ground level pool under deciduous trees had the clumps of black dust. I returned to the first pool, and stuck a finger in the middle of a cluster. Two dozen black specks dotted my finger.

Weird, I thought, but a ruby-crowned kinglet came and fussed at me from the Mexican Rosewood. Distracted, I watched him flit about, and imagined him saying as he grumpily muttered, "Now then, under this leaf ought to be a bug egg, I wish that ugly guy would quit looking at me... where are those eggs?" Then I remembered the black specks, and looked at my finger. Only a half-dozen remained. As I examined my finger -- SPROING!!!!, one went flipping away.

I fetched a cup, and then dipped into the water, captured several hundred of the black specks and went into the house to set up the microscope. I put the black specks into a petri dish, and by the time I was ready to examine them, all of them had drifted to the center of the dish and coalesced into a tight wad. I stirred the petri dish. The specks separated with the motion but when I stopped, back together they came. I could see no means of propulsion.

SPROING!!! Two flew out of the petri dish, and were lost to sight. I put the dish under the microscope, focused it carefully, and adjusted the light. Springtails! I had seen their picture in insect guides, and remembered a little about them, but never before had I found them. Springtails are everywhere, except in the ocean. Some even live in Antartica! They live in the soil, or on the surface of freshwater. Soil springtails eat fungi, dead leaves, spores, bacteria, animal waste, their own waste and molted skins. They are the major decomposers in the soil. In one study in a grassland habitat, over 250 million were estimated to live in just one acre of soil. Water surface dwelling species eat rotifers, paramecium, algae, and bacteria.

I peered though the microscope. About 30 percent were motionless. The others constantly wriggled. "What in the --? My word, is that one eating another one? Yes, By gosh, his leg just disappeared! Was he different from the predatory one?" He looked the same, but then in arthropod identification species are often separated only by the shape of their sexual organs, or by some other physiological feature discernable only by microscopes more powerful than a dissecting scope.

Were these springtails adapted to water? Water springtails, according to the invertebrate taxonomy books I had on hand, are supposed to have a tube at their first body segment that sticks down into the water to anchor them. These did not. Most of them were on their sides, upside down, or on top of one another. I could, however, see their furcula. No, that is not a private part -- a furcula is their spring, the lever that is jammed into a body segment, holding tension until released, when it flips them high into the air. They can flip eight inches -- 128 times their body length.

I noticed as I dipped the springtails out of the water that little white flecks were among the specks. Under the scope the white flecks turned into molted skins. Immature springtails look like adults. They molt into adulthood, gaining the ability to mate. One species of springtail is known to molt 52 times and live a year.

Springtails reproduce with a month of hatching. The males wander around, leaving spermatophores all over the place. The female comes along and picks them up with her ventral tube (her anus). Eggs are later deposited willy-nilly. Some springtails are parthenogenetic, without males, but they live deep in the soil. In most places there are several species of springtails.

Springtails can digest toxins. Research is being done to learn how to luse them in bioremediation, cleaning up oil and chemical spills. Some species eat nematodes that injure plants, and research in "domesticating" these might benefit us as well. Some species of springtails control other species. They release chemicals either into the air, or into the soil, and the second species can no longer reproduce.

Remember the cannabilism I noticed? The theory has been advanced that it is caused by chemicals released by another species. Springtail blood is toxic, so when cannibalism occurs, a population crash is immediate. The species that released the chemical then increases.

Springtails are not quite insects. They have six legs, antennae, and proper insect mouthparts, but have no Malpighian tubules, only six body segments instead of eleven, and their eggs cleave differently when they hatch. What bizarre creatures! (And they lurk in your backyard!)