Ammophila hirsuta is not rare in the plain, but is always found singly on the edge of a road or on sandy slopes, now digging a well, now dragging a heavy prey. It is solitary, like Sphex occitanica, and I was greatly surprised by finding such a number gathered under one stone at the top of Mont Ventoux. Instead of my solitary acquaintance, here was a great assembly. Let us try to educe the probable causes of this agglomeration. By an exception very rare among mining Hymenoptera, Ammophila hirsuta builds in the first days of spring. Toward the end of March, if the season be mild, or at least in the first fortnight of April, when the grasshoppers take their adult form, and painfully cast off their first skin on their thresholds,—when Narcissus poeticus expands its first flowers, and the bunting utters its long-drawn note from the top of the poplars in the meadow,—Ammophila hirsuta sets to work to hollow and provision a home for her larvæ, whereas other species and the predatory Hymenoptera in general undertake this labour only in autumn, during September and October. This very early nidification, preceding by six months the date adopted by the immense majority, at once suggests certain considerations. One asks if those found burrowing so early in April are really insects of that year—i.e. whether these spring workers completed their metamorphosis and came out of their cocoons during the preceding three months. The general rule is that the Fossor becomes a perfect insect, leaves its burrow, and occupies itself with its larvæ all in one season. It is in June and July that the greater part of the hunting Hymenoptera come from the galleries where they lived as larvæ, and in August, September, and October they follow their occupations as burrowers and hunters. Does a similar law apply to Ammophila hirsuta? Does the same season witness the final transformation and the labours of the insect? It is very doubtful, for the Hymenoptera, occupied with mining at the end of March, would have to complete their metamorphosis and break forth from the cocoon in winter, or at latest in February. The severity of the climate at that date forbids any such conclusion. It is not when the bitter Mistral howls for a fortnight at a time and freezes the ground, nor when snow-storms follow its icy breath, that the delicate transformations of the nymph state can take place, and the perfect insect venture to quit the shelter of its cocoon. It needs the soft dampness of earth under a summer sun before it can leave its cell.