The paper relates to the development of one of the most singular and interesting of North American insects–the largest of the Order Neuroptera. In its perfect state this insect is a great, clumsy, nocturnal fly, popularly called Hellgrammite, and charecterized by the jaws of the male being converted into a pair of long, curved, cylindrical and tapering prehensile organs, like the finger of a grain-cradle. In the larva state it is aquatic and much esteemed as fish-bait by fishermen, who call it a “crawler,” “dobson,” etc. Indeed, one of the most popular artificial fish-baits is a patent india-rubber imitation of it.