Adult wireworms, which are commonly called
click beetles, do not generally cause economic damage on established mint in the Pacific
Northwest, but larvae can be found feeding on mint roots, rhizomes, and stems at the soil
surface. Serious infestations occasionally occur on first year mint following potatoes,
onions, sugarbeets, grass seed, or mint planted in newly recovered land after fallow. The
most common species encountered in mint include the Pacific Coast wireworm, Limonus
canus, the sugarbeet wireworm, L. californicus, and the Great Basin
wireworm, Ctenicera pruinina.
The adult beetles are slender, tan to nearly black, and range from 1/2 to 3/4 inch long.
Larvae are hard, segmented, measure 1/2 to 1 inch long, and vary from yellow to brown.
Larvae have three pairs of legs and the last abdominal body segment is elongated and may
end in a keyhole-shaped structure.
Wireworms overwinter as larvae or as recently developed adults which do not emerge from
the soil until the following spring, usually from early May to June. Adults migrate by
flying within fields or to new fields. The females mate and burrow into the soil to
deposit eggs. Eggs are laid singly 2 to 6 inches deep in the soil and hatch in 3 to 4
weeks. The larvae move easily through the soil in search of food. They can feed in the
soil for 2 to 5 years before pupating in July or August. In the Northwest, most wireworms
take about 3 years to complete their life cycles.