Various ichneumonoids are used as biological control agents in controlling horticultural or forest pests. An example is the relationship between the species "Ichneumon eumerus" and its host butterfly "Phengaris rebeli". The butterfly larva is a parasite within "Myrmica" ant nests. The adult "I. eumerus" searches for ant nests and only enters when they contain "P. rebeli" caterpillars. Once inside, they oviposit within the caterpillars and escape the nest by releasing a chemical which causes the worker ants to fight each other rather than the intruding wasp. The wasp eggs then hatch inside the caterpillar and eventually consume and kill the host.