The most important Hymenopterous pests are the sawflies or Tenthredinidae, which in their larval stage attack almost all vegetation.
No doubt large numbers are devoured by insectivorous birds, mammals and reptiles, but the mortality due to them and other foes sinks into insignificance beside that caused by the persecution of hymenopterous insects of the families Ichneumonidae and Pompilidae, especially of the latter, many species of which systematically ransack the country for spiders wherewith to feed their young in the breeding season.
It lives in the grub of a gall-midge and it ultimately becomes changed into the usual white and fleshy hymenopterous larva.
Among the numerous insects parasitic on the inhabitants of galls are hymenopterous flies of the family Proctotrypidae, and of the family Chalcididae, e.g.
Hartig, Die Familien der Blattwespen and Holzwespen (Berlin, 1860); Walsh, " On the Insects, Coleopterous, Hymenopterous and Dipterous, inhabiting the Galls of certain species of Willow," Proc. Ent.