188 TRANSFORMATIONS OF INSECTS. 
office of the parasitic //ymenoptera becomes most evident, and they 
evidently render us most important services, for they check the 
ravages of the larve which destroy cereals, vines, and vegetables 
of all kinds. The balance of life between the vegetables, the 
caterpillars, and the parasites is most extraordinary. A few cater- 
pillars come from the egg of one butterfly, perhaps in a newly 
cultivated district, and they are not noticed. The next year hun- 
dreds of caterpillars are found devouring everything, and then 
one or two stray /chneumons come upon the scene. They are so 
clever that they never miss their aim, and they lay thousands of 
eggs in as many caterpillars. The year following there are fewer 
caterpillars, and a great host of /chneumons, that riddle every 
insect that comes in their way. Spring comes round again, and 
there are no caterpillars, vegetation flourishes, and then comes the 
turn of the parasites. Their office is completed, and they pass 
away. It is thus that armies of caterpillars suddenly appear and 
disappear. 
There is some difficulty in applying the word parasite to all 
insects that live in intimate relation with others. The parasite just 
noticed lives at the expense of the vital juices of its victim or host. 
It does not devour the body, and then remain glutted. But many 
insects, like human parasites, only eat the provisions which others 
have laid up in store for the rainy day, or for their offspring, and 
these, of course, should be called the true parasites. Others live 
with their strange companions, and look out for scraps, and what 
happens to come in their way, these are comrades, and are very 
common in many families of the Articulata. 
The /chneumonide have, as a rule, long thin bodies, slender 
legs, very large wings, which are much veined, and long, slender, 
vibrating, thread-shaped antenne. Agility is written in every 
structure of the /chneumons ; the jaws have long palps; and the 
slender body, large wings, and the legs, which can be used for run- 
ning, indicate unusual locomotive powers. The lively appearance 
of the insects is heightened by their projecting eyes and the long 
and restless antenne. They are not to be caught readily, but 
rush off with wonderful rapidity out of the way of danger, and 
if a female is seized she endeavours to stick her ovipositor into 
the fingers of her captor. 
