Spider mites
Almost invisible without a hand lens. Yellow-green to red-orange specks running along the underside of the long strappy leaves. The huge surface area of arching variegated foliage gives mites more real estate than most houseplants, and dry winter heat triggers a population boom.
Pale tiny pale dots along the green stripe of variegated leaves, then visible bronzing as colonies grow. Fine webbing strung between leaf tips and along the runner stalks. Heavy infestations stop the plant from sending out new runners and plantlets, which is the whole point of growing a spider plant.
Shower the leaves weekly for 3 weeks
Take the spider plant to the shower or sink. Spray cool water on the underside of every leaf and along each runner for 30 seconds. Spider plant leaves are tough and love the rinse. Mites can't reattach quickly when knocked off, and the humidity slows survivors. Repeat weekly for 3 weeks.
Neem oil at lights-out, every 5 days for 3 rounds
Mix 2 tablespoons cold-pressed neem oil and 1 teaspoon dish soap per gallon of water.
Spray top and bottom of every leaf and coat the runner stalks at lights-out, since plantlets along the runners are also infested.
Repeat every 5 days for 3 rounds. That covers the full egg-to-adult cycle.
Raise humidity above 50%
Run a humidifier near the plant for 50 to 60% relative humidity. Spider plant is a tropical understory plant and tolerates dry air better than most, but the dry winter heat that breaks 30% humidity is exactly the climate mites need to breed fast.
Pyrethrin sprays from the hardware store kill them.
Spider mites are arachnids, not insects, so most household bug sprays barely affect them. Use neem oil or a true miticide instead. Spider plant's tough leaves tolerate spinosad too if neem isn't enough.
