From my childhood to the present day, what has appealed to me most about the field of entomology is that there really are new discoveries to be made in my own backyard. In my back yard, down in the muskeg just below my office on Ski Hill Road, and on about half of the land area of the Kenai National Wildlife Refuge, lives a tiny, enigmatic animal about which almost nothing is known.
Only about two millimeters long, yellowish green, and plump, it is one of a group of minute, easily overlooked invertebrates called globular springtails. Springtails possess a special appendage on their abdomens called a furcula that enables them to jump, hence their name. Most of the time, a springtail holds its furcula tucked up under its abdomen in a “cocked” position so that, when the springtail is alarmed or disturbed, it can instantly jump up to several inches. A springtail that jumps 3 inches is the equivalent of an average human jumping almost the length of a football field!
I became interested in these globular springtails as I learned of their ubiquity on our landscape. As part of the Refuge’s Long Term Ecological Monitoring Program, we collected sweep net samples of more than 15,000 arthropods on a grid of sites over 2 million acres in 2004 and 2006. It quickly became apparent as we looked through these samples that globular springtails were extremely common.
I mailed some of these off to Dr. Richard Snider at Michigan State University, an expert in springtail taxonomy. He identified the most common species as Sminthurus sp. A, a species that, although already included in a published identification key to the Sminthurus species of North America, has neither been formally described nor given a valid scientific name.
We collected this species at 112 out of 255 sites (44 percent). This means that at any random spot on the Kenai Refuge, the chance of Sminthurus sp. A being there is almost 50/50. Where we did find them, we picked up an average of 9.3 individuals per 100 square-meter sweep net sample, a density of 380 springtails per acre. Their true population density is almost certainly much greater because we probably collected only a fraction of the individuals that were actually present.
On the Kenai, our Sminthurus appears in early June and is present on vegetation throughout the summer. It is most abundant in spruce muskegs with a low shrub understory. Currently they are plentiful on foliage of dwarf birch in local wetlands.
Because our Sminthurus is so widespread and numerous on the Kenai, I am curious about its ecological role here. Sminthurus species are often collected from plants or soil, but little is known of their biology.
The only well studied species in this genus is Sminthurus viridis, the lucerne flea. Native to Europe, the lucerne flea has now been introduced into many parts of the world including Africa, the Americas, and Australia. In Australia it is a major agricultural pest, especially on clover and alfalfa, reducing crop yields by up to 50 percent. Lucerne fleas strip off the upper photosynthetic layers from leaves of legumes, pasture grasses, and cereal grains, leaving clear windows in the leaves. This reduces the amount of energy the plants can capture by photosynthesis, cutting their productivity.
Although a few species of predatory mites do act as biological control agents of lucerne fleas, reducing their numbers in some agroecosystems, the mites often fail to control this pest. Pesticides are generally used to control lucerne fleas. I don’t know if our Sminthurus species is an agricultural pest, but I have heard that a different species of globular springtail has damaged peonies locally.
So far I have been frustrated in my attempts to observe Sminthurus feeding in the wild. The little springtails wander about quite busily on foliage and stems of dwarf shrubs, apparently searching endlessly but never finding their object, at least not while I am watching. Leaf damage on these shrubs that I at first suspected might be due to springtails I have since attributed to other species.
I have had more success in the lab, where the springtails readily consume leaves of cloudberries and lowbush blueberries offered to them, but this may not reflect their feeding preferences in nature. My impression is that our Sminthurus is a generalist herbivore of low-growing shrubs like dwarf birch and lowbush blueberries, but a definitive answer will require a little more backyard entomology.
Matt Bowser serves as Entomologist at the Kenai National Wildlife Refuge. For more detailed information about the Refuge, you can check http://kenai.fws.gov or on Facebook at http://www.facebook.com/kenainationalwildliferefuge.