Nocturnal Leaf-Eating Insects on Your Houseplants

Dining After Dark

• Two very different pests enjoy after-dark feasts on your houseplants' tab. Earwigs are flat, 3/4-inch reddish-brown insects with curved pincers protruding from their tail ends. During the day, they remain concealed in moist planting medium or in the water-collection saucers underneath plant pots. At night, they emerge and devour any sap-draining aphids they find. In the absence of aphids, earwigs will eat foliage. Their calling cards are leaves with irregular holes or chewed margins. Black vine weevils -- hard-shelled, 1/2-inch gray to black beetles with long, narrow snouts and angled antennae -- very occasionally infest houseplants. Weevils chew U-shaped slices on the edges of leaves at night.

Where They Came From

• Given the option, earwigs would spend their lives life in the cool, dark, moist recesses of your garden soil. Hot, dry conditions, however, force them to search for moisture indoors, where they soon starve without damp paper and cardboard or plants on which to feed. Black vine weevils normally stay outdoors, with adults laying eggs in the soil during summer. The larvae remain in the soil, devouring roots and pupating until they emerge as adults the following spring. The only houseplants likely to host black vine weevils are those that have spent time on an open porch or patio.

Eliminating Earwigs

• Once earwigs have infested a houseplant, insecticide bait isn't likely to interest them. Trap the adults by stuffing 4-inch flowerpots with moistened, crumpled newspaper, setting them upside-down around the bases of your plants and propping them open with sticks. Earwigs crawl into the dampened paper after their nightly feeding; dump the pot’s contents into soapy water to kill them. To eliminate eggs and nymphs, remove and replace the top 3/4 inch of your infested plants’ growing medium. As an extra precaution, let the top 2 inches of medium dry to the touch before watering. The eggs and nymphs can't survive without moisture.

Beating Black Vine Weevils

• Root-feeding black vine weevil larvae pose a much greater threat to your houseplants than their leaf-feeding parents. Adult weevils hide beneath the leaves or in litter at the base of the plants during the day, and feed nightly for three to six weeks before laying eggs. To kill them before they reproduce, place a white cloth around the base of each affected plant at the first sign of leaf damage. When the pests emerge to feed, shake them from the leaves onto the cloth and drown them in soapy water. Insecticides have little effect on black vine weevils.

Caterpillars

• Although cutworm moths don't feed on houseplants, their caterpillar offspring occasionally do. Cutworm caterpillars hide on the lower stems or just beneath the soil during the day; you'll recognize them from the C-shape they adopt when disturbed. At night, some species chew holes in foliage. Pesticides aren't much use against them, but controlling the caterpillars is as easy as handpicking and dropping them into a jar of rubbing alcohol.