214. DISEASES OF INSECTS. 
furnished with a footstalk terminating in a bulb’, which 
is so deeply and firmly fixed that it is nnpossible to ex- 
tract it without detaching a portion of the animal with 
it, and even when the caterpillar changes its skin it is not 
displaced. After it is hatched, the grub, while feeding, 
keeps its posterior extremity in the egg-shell, to which 
it adheres so pertinaciously, that it is scarcely possible 
to disengage it without crushing it. It fixes itself by its 
mandibles to the skin of the caterpillar, and keeps con- 
stantly sucking the contents of its body till it dies: some- 
times nine or ten of these larvee inhabit a single caterpil- 
lar>. Reaumur has given an accountof other external Ich- 
neumons. Upon one caterpillar that he examined, they 
were so numerous as to render the poor animal quite a 
spectacle, and they underwent their metamorphosis at- 
tached toit*. One species of this description avenges the 
cause of insects upon their most pitiless foes, the all-de- 
vouring spider—for in the midst of her toils and lines of 
circumvallation it makes her its prey. De Geer, meeting 
one day with a young spider of a common kind, observed 
with surprise, engaged in sucking it, a small white grub, 
which was firmly attached to the abdomen near the trunk. 
Putting it by im a glass, after some days he examined it 
again; when he observed that it had spun the outline of 
a vertical web, had stretched threads from the top to the 
bottom of the glass and from one side to the other, and 
had also spun the radii that meet in the centre, and this 
was all ;—but what was remarkable, the larva that had 
fed upon it was suspended in the centre of this web, 
where it was engaged in spinning its own cocoon, while 
* Pirate XX. Fie. 22, a, > De Geer ii. 850—.— 
© Reaum. i. 444— 
