Daylilies are one of the most pest-free and care-free plants in the perennial garden. Occasionally, though, they may be afflicted by one of several pests that can pose a threat to their appearance, bloom or overall health.
Daylily pests, according to the American Hemerocallis Society, "include insects, mites, molluscs, millipedes and mammals" that feast on the plants or make homes in them. European earwigs, for example, are an insect about 3/4 inch long with pincers on their rear ends that chew holes in leaves and feed on daylily flowers at night.
Slugs may be pests where daylilies are close to hostas.
Aphids are a common insect pest; both adult and larval forms feed on leaves. Spider mites are tiny arachnids that feed on the undersides of leaves. Slugs feed at night on the undersides of leaves, making holes or shredding them. Hemerocallis gall midge, a European pest that has invaded Eastern Canada and the Northeastern U.S., lays eggs that become larvae that feed on leaves.
Fungus gnats deposit eggs that hatch into larvae that eat the roots and crown of daylily plants; root-knot nematodes can kill entire plants. The largest pests are deer, who feed on tender new growth in spring.