The large number of species in Ichneumonidae may be due to the evolution of parasitoidism in hymenoptera, which occurred approximately 247 million years ago. Ichneumonidae is the basal branch of Apocrita, the lineage in which parasitoidism in hymenoptera evolved, and some ichneumonids are thought to have been in stasis for millions of years and closely resemble the common ancestor in which parasitoidism evolved. This common ancestor was likely an Ectoparasitoid woodwasp that parasitized wood-boring beetle larvae in trees. The family has existed since at least the Early Cretaceous ( 125 mya), but probably appeared already in the Jurassic (c. 181 mya), soon after the appearance of its major host groups. It diversified during the Oligocene.