With the arrival of spring, many people will be heading outdoors to work on their gardens and lawns. While digging around in the soil, you many encounter some creatures that you rarely see above ground. Here are some common critters found underground in the Washington, DC area.
Scarabaeidae larvae: These soft, white grubs are the larvae of various species of scarab beetle. Their size varies by the age and species of the grub. The species can be determined by the pattern of hairs and spines on the underside of their last abdominal segment; common species in this area include the Japanese beetle, northern masked chafer, and green June beetle. They are a common sight in lawns, where they feed on the roots of grass.
Most of these species have a 12-month life cycle. The adult beetles lay their eggs in the summer, and when the grubs hatch, they move underground and spend the winter deep in the soil. When the weather warms, they move up towards the surface and resume feeding before pupating in late spring. Because they feed on grass roots, a heavy infestation of grubs can damage lawns, causing patches of dead, spongy turf.
Elateridae larva: This slender, reddish-brown creature, commonly called a wireworm, is the larva of a click beetle. The adults also spend most of their time in the soil, where they lay their eggs in the spring. The hatched larvae spend about 2 - 6 years underground, feeding on plant seeds, stems, and tubers. This habit makes them an agricultural pest to certain crops, especially corn and potatoes.
Carabidae larva: This is the larva of the family Carabidae, commonly known as ground beetles. They are a very large and diverse family, with over 2,000 species in North America alone. As with many beetle larvae, species determination is difficult for non-experts. They spend the entire larval stage underground, undergoing several instar stages before pupating. Many carabid beetles, both larval and adult, are predatory, but they have also been known to consume plants and seeds.
Earthworm: Earthworms are not insects, or even arthropods, but they are frequently lumped in with the common term "bugs." They lack the jointed exoskeleton of insects; instead, their shape is maintained by a series of fluid-filled chambers. They move through the soil using muscular contractions, consuming organic matter and expelling waste as they go. This circulation of organic material enriches the fertility of the soil, making earthworms a welcome addition to most gardens.
These are just a small sample of the insects that can be found under the soil. While some may be agricultural pests, they are also a vital food source to larger animals, such as moles, birds, and even humans.
Erin K. Kolski, Department of Entomology, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA.
All photos: Erin Kolski