Biological control of swift moth caterpillars

To naturally control caterpillar populations, encourage predators like birds, wasps, hedgehogs, and ground beetles into the garden. Hedgehogs like dense undergrowth and grasses for hiding and nesting. You can also build or purchase hedgehog homes. 

A mix of pathogenic nematodes can be purchased from biological control suppliers. These microscopic organisms enter caterpillar bodies and infect them with a bacterial disease. Water in nematodes between mid-spring and early autumn on moist soil when temperatures are between 12-20C (54-68F). Apply as soon as possible after purchase.