Pine and oak processionary caterpillars cause serious harm to trees and severe health risks to humans and animals, yet their control raises ethical questions about large-scale insect killing.
Processionary caterpillars must be controlled in areas where they pose health risks to humans and animals. The welfare question is about proportionality and method. Broad-spectrum chemical spraying kills far more insects — including many non-target and beneficial species — than targeted biological controls. Pheromone traps and Bt applications are more targeted. The precautionary principle suggests using the least harmful effective method, even for pest species.