For outdoor trapping, place the jars in trees and tree holes, in the mulch next to the house, and near the garbage disposal and air conditioning pad. Cover the jars with a dome shaped piece of aluminum foil taped to the sides. This will prevent rain from filling the traps. Biocontrol Biological control of cockroaches is generally not realized as a source of cockroach control because it is usually present and thus taken for granted. Almost all animals have natural enemies that attack and kill them.
Cockroaches are no exception.
The conservation of cockroach natural enemies will help keep infestations in check. Parasitic wasps are the most important natural enemy listed. Parasitic nematodes occur in very large numbers. Nematodes enter the cockroach gut either through the cockroaches' air tubes or directly through the mouth. Nematodes attach to the cockroach exoskeleton and the cockroaches groom them off.