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-grey colour, not unlike that of the House-fly. 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. So 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 grey 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 were slaughtered in passing through the entrance-hall or lower down, they would fall to the bottom of the burrow promiscuously with the other rubbish. Now in this charnel-pit, as I said, there are never any dead Volucellæ, never a Fly of any sort. The incomers, therefore, 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 larvæ of the Wasp, it is some time before they are suffocated by the petrol; and the great majority 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 infant grubs.