Biological Caterpillar & Webworm Control targets “soft-bodied” insect pests. Instead of poisoning, the oil suffocates or “smothers” these insects and their eggs. The oil spray blocks an insect’s air holes (spiracles), causing it to die from asphyxiation. These oils kill a wide variety of insect pests such as aphids, scale, adelgids, whiteflies, spider mites, mealybugs, thrips, and more. As horticultural oils must cover the target pest to be effective, there is no long term residual effect.