HYMENOPTERA . 
6 i S 
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 antennas 
are rust-red, with broad black FlG - 744 -— Tremex columba. 
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 Sirex (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 
