Female adult giant ichneumon wasp (Megarhyssa spp.) on a dead American elm tree (Ulmus americana), showing its entire egg-laying ovipositor and looking to lay its eggs in the tree. Ichneumon wasps range throughout the world and United States, except the plains, deserts and lower southwest. In the spring the adult emerges from decaying logs, dead or dying broad-leafed trees, and forest canopies to begin looking for a mate. After mating (rarely observed and believed to last 10-20 seconds) the wasp looks for a suitable dead tree (usually an elm tree), where it tries to locate a horntail fly larvae inside the dead tree. After locating the horntail larvae, the wasp then drives its ovipositor into the wood and deposits an egg in the horntail's larvae tunnel. As the ichneumon deposits its egg, the overpositor is withdrawn from the wood into an expandable sac at the end of its tail. The egg then developes into a larva as it consumes the horntail's larva. Throughout the summer and winter, the larva pupates into an adult where it bores its way out of the tree trunk the following spring as an adult. Summer, Ludlow, MA, USA.