Certain of the nesting habits of the wasp, Sphex xanthopterus (Cam.), have been observed at and near Los Angeles, California. The insect nests for the most part in the moist or wet, sandy soil of the river bed. It digs a short tunnel and enlarges it into a cell at the end. Into this is stored a stung lepidopterous larva, often the young of the moth, Zale lunata (Drury) and its varieties, to the side of which is fastened the egg of the wasp. The entrance to the tunnel and nest is then closed and in due time, if all goes well the egg hatches, the larva devours the prey, spins its cocoon, pupates, and later emerges an adult wasp. A more detailed account of some of the facts in its nesting habits and life history is given below.