HYMENOPTERA. 



615 



FlG. 744. — Tremex columba. 



typical species is The Pigeon Horn-tail, Tremex columba 

 (Tre'mex co-lum'ba). The body of this insect is cylindri- 

 cal, as large around as a me- 

 dium-sized lead-pencil, and 

 at least an inch and a half 

 long (Fig. 744). The thorax 

 and head are rust-red and 

 black. The abdomen is black, 

 with ochre-yellow bands and 

 spots along the sides; the 

 horn at the hind end of the 

 body is yellow; the antennae 

 are rust-red, with broad black 

 rings at the middle. The wings are smoky color and trans- 

 parent ; the legs are dull yellow. The female pierces the 

 wood of a tree to the depth of half an inch, where she de- 

 posits her eggs ; sometimes her ovipositor gets wedged in 

 the wood and holds her there a prisoner until she dies. 

 The grub is cylindrical and whitish, and attains the length 

 of an inch and a half ; it does great injury by perforating 

 trees, especially elms. It transforms within a cocoon made of 

 silk and fine chips. When the fly emerges it breaks through 

 the cocoon, creeps to the mouth of the burrow, gnaws 

 through the bark, and flies off. 



The preceding is the only species of Tremex that occurs 

 in our fauna. In this genus there is a single closed marginal 

 and two closed submarginal cells. The Horn-tails of the 

 genus 5z7r.*r (Si'rex), of which we have many species, closely 

 resemble Tremex in form, but differ in having two marginal 

 and three submarginal cells. 



Family Cynipid^e (Cy-nip'i-dae). 



The Gall-flies. 



These insects are termed gall-flies because the majority of 

 the species live within galls ; but it should be remembered 



