Another hunting wasp, the Hairy Ammophila, subdues a large caterpillar
into a state of coma by pricking with its sting nine of the ventral
ganglia, while it spares the cervical ganglion, merely compressing
the latter with its mandibles, so as not to destroy life altogether.
This nice discrimination rules out Loeb’s hypothesis of a so-called
“chemotaxis.” As a result of this elaborate surgical operation, the
power of movement is suppressed in every segment, and the tiny larva
of the wasp emerging from the egg laid on the ventral surface of the
caterpillar can devour this huge living, but motionless, victim in
peace and safety. Dead meat would not agree with the larva, and any
movement of the caterpillar would be fatal to the delicate grub. To
eliminate these contingencies, the Wasp’s surgery must be perfect
from the very outset. “There is,” says Fabre, “no _via media_, no
half success. Either the caterpillar is treated according to rule and
the Wasp and its family is perpetuated; or else the victim is only
partially paralyzed and the Wasp’s offspring dies in the egg. Yielding
to the inexorable logic of things, we will have to admit that the
first Hairy Ammophila, after capturing a Grey Worm to feed her larva,
operated on the patient by the exact method in use today.” (“The
Hunting Wasps,” pp. 403, 404.)
Certain meticulous critics of our day cite the fact of the diffusion
of the poison as indicating that the surgery of the hunting wasps need
not be so perfectly accommodated to the nervous system of their prey,
and they attempt in this way to discredit Fabre as having failed to
take the occurrence of diffusion into account. A careful reading of
his works, however, will serve to vindicate him in this respect. In a
chapter on the poison of the bee, for instance, we read: “The local
effect is diffused. This diffusion, which might well take place in the
victims of the predatory insects, plays no part in the latter’s method
of operation. The egg, which will be laid immediately afterwards,
demands the complete inertia of the prey from the outset. Hence all the
nerve-centers that govern locomotion must be numbed instantaneously
by the virus.” (“Bramble Bees,” p. 347.) Bouvier, therefore, very
justly remarks: “After all, when Fabre’s work is examined there is no
trouble in seeing that none of these details escaped him. He never
disputed the paralytic action of the poison inoculated by the insect,
and the wonderful researches by the Peckhams on the Pompilids, which
hunt Lycosids, have clearly established the fact that the thrusts of
the sting given by the predatory insect produce two different kinds
of paralysis, one functional, and often temporary, resulting from the
action of the venom, the other structural and persistent, produced by
the dart which more or less injures the nervous centers.” (Smithson.
Inst. Rpt. for 1916, p. 594.)
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