my immediate concern. The bumblebee fly did not appear. The
period for her visits had doubtless passed; for I found plenty of her
grubs when the nest was dug up.

Other flies rewarded me for my assiduity. I saw some--at a respectful
distance, I need hardly say--entering the burrow. They were
insignificant in size and of a dark gray color, not unlike that of the
housefly. They had not a patch of yellow about them and certainly had no
claim to protective mimicry. Nevertheless, they went in and out as they
pleased, calmly, as though they were at home. As long as there was not
too great a number at the door, the wasps left them alone. When there
was anything of a crowd, the gray visitors waited near the threshold for
a less busy moment. No harm came to them.

Inside the establishment, the same peaceful relations prevail. In
this respect I have the evidence of my excavations. In the underground
charnel house, so rich in Fly grubs, I find no corpses of adult flies.
If the strangers had been slaughtered in passing through the entrance
hall, or lower down, they would fall to the bottom of the burrow anyhow,
with the other rubbish. Now in this charnel house, as I said, there are
never any dead bumblebee flies, never a fly of any sort. The incomers
are respected. Having done their business, they go out unscathed.

This tolerance on the part of the wasps is surprising. And a suspicion
comes to one's mind: can it be that the Volucella and the rest are
not what the accepted theories of natural history call them, namely,
enemies, grub killers sacking the wasps' nest? We will look into this
by examining them when they are hatched. Nothing is easier, in September
and October, than to collect the Volucella's eggs in such numbers as we
please. They abound on the outer surface of the wasps' nest. Moreover,
as with the larvae of the wasp, it is some time before they are
suffocated by the petroleum fumes; and so most of them are sure to
hatch. I take my scissors, cut the most densely populated bits from the
paper wall of the nest and fill a jar with them. This is the warehouse
from which I shall daily, for the best part of the next two months, draw
my supply of nascent grubs.

The Volucella's egg remains where it is, with its white color always
strongly marked against the brown of the background. The shell wrinkles
and collapses; and the fore end tears open. From it there issues a
pretty little white grub, thin in front, swelling slight