42 NORTH AMERICAN DIPTERA. 



resemblance to certain hymenopterous insects. Species of 

 Rhachicerus form a connecting link with the Nematocera, and 

 are apt to be confounded with the Khyphidae, but the presence 

 of the pulvilli will distinguish them. The larvae are found 

 in decaying wood or under the bark of trees and are carnivor- 

 ous and predaceous, feeding upon the larvae of beetles and 

 other wood insects. The skin is parchment-like, the body 

 cylindrical. The mouth-parts and antennae are very small, 

 the maxillae short and hook-like. The first or the first three 

 segments back of the head are chitinized above ; the last seg- 

 ment above with a chitiuized plate terminating posteriorly in 

 two hooks. The fourth to the ninth segments have bristly 

 pseudopods below. The pupae are free. 



The Leptiriae comprise something over two hundred known 

 species. They are usually of moderate size and not very active 

 in their habits. The larger species are commonly found in 

 meadows and woodlands, resting upon stems or trunks of trees 

 with their head downward. They are sometimes predaceous 

 upon other insects and the species of Symphoromyia have a 

 habit of sucking blood as do the horseflies. The larvae are 

 predaceous, living in the earth, in decaying wood or in pas- 

 sages made by woodboring beetles. Others live in moss, in 

 sand or in water. The eggs of Atherix are deposited in dense 

 masses attached to dry branches overhanging water. Not only 

 do numerous females contribute to the formation of these 

 masses, but they remain there themselves and die. The larvae 

 hatching, escape into the water. The flies of species of Ver- 

 mileo deposit their eggs in sand, and the larvae form conical 

 pitfalls in which to ensnare small insects. The tenth seg- 

 ment of these larvae bears above at its tip a transverse row of 

 long booklets directed backward, but with the hooks bent 

 forward; the eleventh segment has a similar row directed 

 forward, the hooks of which are turned backward. On the 

 fifth segment below there is a simple unpaired grasping foot 

 which is capable of being protruded forward and downward ; 



