Moles

Although moles are very common in Western Washington, they are rarely seen due to their subterranean lifestyle. But you usually know when they're around. As moles excavate and maintain their underground burrow systems, excess soil is pushed to the surface forming molehills.

Two species—the Townsend's Mole and the Coast or Pacific Mole—are responsible for building the molehills in Washington State. A third species, the Shrew Mole, does not build extensive burrow systems, but spends time on the soil surface or under leaf litter.

Moles are highly specialized digging machines. They have broad, shovel-like forelimbs that allow them to power through soil. Although those who maintain gardens or lawns often view moles negatively, the burrowing is actually beneficial. It aerates and mixes soil layers and improves drainage. In addition, moles feed primarily on invertebrates, including the insect larvae, such as Crane Flies, which damage roots.

Moles are generally solitary, and aggressively defend their burrow systems. Mating season, in January and February, is an exception, when males will seek out females. Females give birth about 4 to 6 weeks after mating. Young moles spend 30 to 36 days with their mothers before dispersing to find their own territories. When they disperse, the young moles usually move above ground at night where many fall prey to owls, coyotes and other nocturnal predators.

Solving and preventing conflicts

Most conflict situations have to do with the molehills. Moles do sometimes harm plants, although inadvertently, by uprooting or covering them up as they diligently excavate. Moles do occasionally eat plant matter such as roots, tubers and bulbs. The presence of moles, however, is likely to be more helpful than harmful to the health of the soil on your property.

Excluding moles from your entire yard is difficult, but there are ways to prevent them from gaining access to your flower or vegetable gardens.

Create raised beds for your garden and ornamental plants. If you attach one-inch galvanized or vinyl coated hardware cloth to the bottom of the raised bed, moles will be effectively prevented from digging up from below.
Use a mole repellant. According to the Washington Department of Fish and Wildlife (WDFW) there are commercially available castor oil-based repellents that have been scientifically tested on moles in the Eastern U.S. with some success. Or try this homemade repellant suggested by WDFW.
Try other commercially available products such as mechanical "thumpers" that send vibrations into the ground that supposedly encourage moles to leave. Some anecdotal evidence suggests these work for small yards, but no scientific evaluation of the products has been done.
The least expensive and most effective way to approach a "mole problem" is to learn to accept their presence. You can remove or tamp down molehills. Inspect your yard regularly and re-bury any exposed roots to mitigate damage to plants. You can transition your yard from a solid green matt of grass to a diverse habitat filled with native plants. The native plantings will thrive in the healthy soil that the moles have helped cultivate, and the local wildlife (including the moles) will thank you!