34Q 



THE STUDY OF INSECTS 



Fig. 577. — Trtmex columba. 



longation. This is short and triangular in the males, and is a prolon- 

 gation of the last ventral segment; in the females it is long and often 



spear-shaped, and is a prolongation of the 



last dorsal segmenl . 



The body is cylindrical (Fig. 577); the 



head large ami widened behind the eyes; 



the pronotum is right-angled, so that it 

 presents both a strictly dorsal and a ceph- 

 alic aspect, the latter concave; vein Sci 

 of the front wing is absent; thepropodeum 

 is divided longitudinally; the anterior 

 tibia? each with only one apical spur; the 

 sheath of the ovipositor is very long and 

 exserted beyond the end of the abdomen; 

 the ovipositor is fitted for boring. 



The Siricida? is a small family; only 

 about fifty species representing five genera are known. 



The larvae bore in the trunks of trees; our best-known species is the 

 following one. 



The pigeon horn-tail, Trcmex columba. — The larva of this species 

 infests maple, elm, apple, pear, beech, oak, and sycamore. The female 

 (Fig. 577) in order to oviposit pierces the wood of a tree to the depth of 

 about \ of an inch; the eggs are laid singly; sometimes her ovipositor 

 gets wedged in the wood and holds her a prisoner until she dies. The 

 larva is cylindrical and attains a length of if inches. It transforms 

 within its burrow, in a cocoon made of silk and fine chips. 



The adults of this species vary in color and marking; based on these 

 variations, three fairly distinct races have been recognized, which to a 

 considerable extent are geographical, although their ranges overlap. In 

 the typical form, race columba, the abdomen is black, with ochre-yellow 

 bands and spots along the sides; this is the common form in Quebec, 

 Ontario, and the northeastern United States. In the race aureus, the 

 ground color of the abdomen is yellow and the markings black; this is 

 the common form in the Rocky Mountains and is found on the Pacific 

 Coast. In the race sericeus, the entire body is fulvous, the legs beyond 

 the femora yellow, and the wings dark reddish-brown; this race is found 

 in the southeastern United States and as far north as Pennsylvania and 

 West to Utah. 



Family Cephid^e 

 The Stem Saw flies 



The stem sawflies are so-called because the larvae bore into the stems 

 of plants or in the tender shoots of trees and shrubs. The adults are 

 slender, elongate insects of moderate size. The pronotum is more or less 

 quadrate and longer than is usual in the Hymenoptera. The anterior 

 tibiae are armed with one terminal spur. 



This family is of moderate size; less than a score of species have been 

 found in our fauna; but these represent nine genera. Some of the species 

 are of economic importance. Several species bore in the stems of grains 

 and grasses. The following species illustrate the habits of these. 



