But in spite of all her caution one danger remains. It sometimes happens, while the Wasp is building, that the approach to the half-built dwelling is barred to her for a time, or even for the whole day, by a curtain of steam or smoke. Washing-days are most risky. From morning till night the housewife keeps the huge cauldron boiling. The smoke from the hearth, the steam from the cauldron and the wash-tub, form a dense mist in front of the fireplace. It is told of the Water-Ouzel that, to get back to his nest, he will fly through the cataract under a mill-weir. This Wasp is even more daring: with her pellet of mud in her teeth she crosses the cloud of smoke and disappears behind it, where she becomes invisible, so thick is the screen. An irregular chirring sound, the song she sings at her work, alone betrays her presence. The building goes on mysteriously behind the cloud. The song ceases, and the Wasp flies back through the steam, quite unharmed. She will face this danger repeatedly all day, until the cell is built, stored with food, and closed. Once and once only I was able to observe a Pelopæus at my own fireside; and, as it happened, it was a washing-day. I had not long been appointed to the Avignon grammar-school. It was close upon two o’clock, and in a few minutes the roll of the drum would summon me to give a scientific lecture to an audience of wool-gatherers. Suddenly I saw a strange, agile insect dart through the steam that rose from the wash-tub. The front part of its body was very thin, and the back part was very plump, and the two parts were joined together by a long thread. It was the Pelopæus, the first I had seen with observant eyes. Being very anxious to become better acquainted with my visitor, I fervently entreated the household not to disturb her in my absence. Things went better than I dared hope. On my return she was still carrying on her mason’s work behind the steam. Being eager to see the building of the cells, the nature of the provisions, and the evolution of the young Wasps, I raked the fire so as to decrease the volume of smoke, and for a good two hours I watched the mother Wasp diving through the cloud. Never again, in the forty years that followed, was my fireplace honoured with such a visit. All the further information I have gathered was gleaned on the hearths of my neighbours. The Pelopæus, it appears, is of a solitary and vagrant disposition. She nearly always builds a lonely nest, and unlike many Wasps and Bees, she seldom founds her family at the spot where she was reared herself. She is often found in our southern towns, but on the whole she prefers the peasant’s smoky house to the townsman’s white villa. Nowhere have I seen her so plentiful as in my village, with its tumble-down cottages burnt yellow by the sun.