In The Dirt: Earthworms and Drought

Hit and miss rain showers and scattered thunderstorms have provided much of the precipitation over the New York State during this past month.

This has allowed some locations to maintain an adequate level of soil moisture while causing conditions in other places to become especially dry.

The lack of periodic soaking rains, along with the abundance of sunshine and long stretches of above average temperatures has impacted the lives of a multitude of soil organisms, particularly earthworms which are highly sensitive to dry conditions.

Earthworms are annelids, or segmented worms, that are well adapted for surviving in soil. The long, narrow, cylindrical body of these creatures is ideally designed to move them vertically through the compacted mass of sand and silt that form the bulk of the soils in places like the Adirondack Park.

As they work their way up and down, earthworms ingest the numerous fragments of once living matter, like rotted leaves, pieces of decaying bark, small chunks of decomposing wood, and a multitude of bacteria and other soil microorganisms. In this way, earthworms greatly facilitate the process of decomposition which helps in the recycling of numerous compounds needed by most plants. Worms also create a labyrinth of small passageways through the soil in which air and water can better travel to the lower levels of the soil where they are essential to the roots of large trees.

Because worms lack the exoskeleton characteristic of arthropods, they are far more prone to dehydration than other soil creatures like beetles, ants, and cicadas. Also, since worms absorb oxygen directly through their skin, it is necessary for them to maintain a certain level of skin moisture in order to allow for the transfer of oxygen into their body.

The sensitivity of worms to dry air results in their nocturnal life style. While their body is not as sensitive to direct sunlight as that of vampires, worms can die from suffocation when exposed to dry, daytime air and the dehydrating effect of the sun for any length of time.

During a period of drought, worms often burrow deep underground in an attempt to reach soil that is not as dry or as hot. In heavily shaded locations, worms may also take refuge beneath a large chunk of rotting wood, a pile of dead leaves, or a dense mat of organic debris as these objects, like a sponge, hold water molecules for long periods and create small moisture oases on the soil’s surface.

Once a worm has located a tolerable place, it curls up into a tight ball and secretes a covering of mucus over its body in an attempt to retain its body moisture. It will also lapse into a state of dormancy, which limits its need for oxygen and food until damp conditions develop again.

The lack of worms coming to the surface at night to feed on fallen foliage and other decaying items causes problems for those numerous forms of wildlife that eat these common soil entities. The woodcock, a bird of alder thickets and damp hardwood forests, depends heavily on worms for nourishment.

The woodcock begins to forage shortly after sunset and again before sunrise in its attempt to encounter and snag these fleshy annelids. The skunk is another creature that prowls lawns and the forest floor after dusk for soil bugs, especially worms during these warmer months of the year. The robin is well known for arising at first light from mid spring until mid summer in its attempt to collect worms which are fed to its nestlings. Both shrews and moles are still other creatures that rely on worms for food during much of the year. When the soil becomes powdery dry and worms become exceedingly scarce, these small mammals can occasionally die of starvation, particularly if drought conditions linger more than a few weeks.

The loss of earthworm activity is only temporary, as these squirmy entities quickly return after a few soaking rains fall across the Park. That time will be to the delight of the many creatures that have come to rely on worms for a source of food, as well as those recreational anglers that enjoy using them as bait to catch fish.

However, the reappearance of earthworms can elicit disappointment in those hardcore, ecological purists that view these annelids as just another invasive species. To some naturalists, earthworms have progressively degraded the quality of the soil in our woodlands since their introduction two centuries ago, and have forever altered the dynamics of the soil in the forested areas of New York States.

Photo of Earthworm courtesy Wikimedia user Aruna.