The larvæ of those moths, such as the Sphinges, or Hawk moths, which spin no cocoon, descend deep into the earth, where they transform into chrysalids and lie in deep earthen cocoons.
The wild bees may now be found frequenting flowers in considerable numbers. Both sexes of the Humble bee, the Leaf-cutter bee, and other smaller genera abound during the warm days.
One's attention during an unusually warm and pleasant day in this month is attracted by clouds of insects filling the air, especially towards sunset, when the slanting rays of the sun shine through the winged hosts. On careful investigation these insects will prove to be nearly all ants, and, perhaps, to belong to a single species. Looking about on the ground, an unusual activity will be noticed in the ant-hills. This is the swarming of the ants. The autumnal brood of females has appeared, and this is their marriage day.
The history of a formicarium, or ant's nest, is as follows: The workers, only, hibernate, and are found early in the spring, taking care of the eggs and larvæ produced by the autumnal brood of females. In the course of the summer these eggs and larvaæ arrive at maturity, and swarm on a hot sultry day, usually early in September. The females, after their marriage flight, for the small diminutive males seek their company at this time, descend and enter the ground to lay their eggs for new colonies, or, as Westwood states, they are often seized by the workers and retained in the old colonies. Having no more inclination to fly, they pluck off their wings and may be seen running about wingless.
Dr. C. C. Abbot gives us the following account of the swarming of a species in New Jersey: "On the afternoon of Oct. 6th, at about 4 P. M., we were attracted to a part of the large yard surrounding our home, by a multitude of large sized insects that filled the air, and appeared to be of some unusual form of insect life, judging of them from a distance. On closer inspection these creatures proved to be a brood of red ants (Formica) that had just emerged from their underground home and were now for the first time using their delicate wings. The sky, at the time, was wholly overcast; the wind strong, southeast; thermometer 66º Fahr. Taking a favorable position near the mass, as they slowly crawled from the ground, up the blades of grass and stems of clover and small weeds, we noted, first, that they seemed dazed, without any method in their movements, save an ill-defined impression that they must go somewhere. Again, they were pushed forward, usually by those coming after them, which seemed to add to their confusion. As a brood or colony of insects, their every movement indicated that they were wholly ill at ease.
"Once at the end of a blade of grass, they seemed even more puzzled as to what to do. If not followed by a fellow ant, as was usually the case, they would invariably fall down again to the earth, and sometimes repeat this movement until a new comer joined in the ascent, when the uncertain individual would be forced to use his wings. This flight would be inaugurated by a very rapid buzzing of the wings, as though to dry them, or prove their owner's power over them, but which it is difficult to say. After a short rest, the violent movement of the wings would recommence, and finally losing fear, as it were, the ant would let go his hold upon the blade of grass and rise slowly upwards. It could, in fact, scarcely be called flight. The steady vibration of the wings simply bore them upwards, ten, twenty or thirty feet, until they were caught by a breeze, or by the steadier wind that was moving at an elevation equal to the height of the surrounding pine and spruce trees. So far as we were able to discover, their wings were of the same use to them, in transporting them from their former home, that the 'wings' of many seeds are, in scattering them; both are wholly at the mercy of the winds.
"Mr. Bates, in describing the habits of the Saüba ants (Œcodoma cephalotes) says,[33] 'The successful début of the winged males and females depends likewise on the workers. It is amusing to see the activity and excitement which reign in an ant's nest when the exodus of the winged individuals is taking place. The workers clear the roads of exit, and show the most lively interest in their departure, although it is highly improbable that any of them will return to the same colony. The swarming or exodus of the winged males and females of the Saüba ant takes place in January and February, that is, at the commencement of the rainy season. They come out in the evening in vast numbers, causing quite a commotion in the streets and lanes.' We have quoted this passage from Mr. Bates' fascinating book, because of the great similarity and dissimilarity in the movements of the two species at this period of their existence. Remembering, at the time the above remarks concerning the South American species, we looked carefully for the workers, in this instance, and failed to discover above half a dozen wingless ants above ground, and these were plodding about, very indifferent, as it appeared to us, to the fate or welfare of their winged brothers. And on digging down a few inches, we could find but comparatively few individuals in the nest, and could detect no movements on their parts that referred to the exodus of winged individuals, then going on.
"On the other hand, the time of day agrees with the remarks of Mr. Bates. When we first noticed them, about 4 P. M., they had probably just commenced their flight. It continued until nearly 7 P. M., or a considerable time after sundown. The next morning, there was not an individual, winged or wingless, to be seen above ground; the nest itself was comparatively empty; and what few occupants there were seemed to be in a semi-torpid condition. Were they simply resting after the fatigue and excitement of yesterday?
"It was not possible for us to calculate what proportion of these winged ants were carried by the wind too far to return to their old home; but certainly a large proportion were caught by the surrounding trees; and we found, on search, some of these crawling down the trunks of the trees, with their wings in a damaged condition. How near the trees must be for them to reach their old home, we should like to learn; and what tells them, 'which road to take?' Dr. Duncan states,[34] 'It was formerly supposed that the females which alighted at a great distance from their old nests returned again, but Huber, having great doubts upon this subject, found that some of them, after having left the males, fell on to the ground in out-of-the-way places, whence they could not possibly return to the original nest!' We unfortunately did not note the sex of those individuals that we intercepted in their return (?) trip; but we can not help expressing our belief that, at least in this case, there was scarcely an appreciable amount of 'returning' on the part of those whose exodus we have just described; although so many were caught by the nearer trees and shrubbery. Is it probable that these insects could find their way to a small underground nest, where there was no 'travel' in the vicinity, other than the steady departure of individuals, who, like themselves, were terribly bothered with the wings they were carrying about with them?" (American Naturalist.)
We have noticed that those females that do not return to the old nest found new ones. In Maine and Massachusetts we have for several successive years noticed the swarming of certain species of ants during an unusually warm and sultry day early in September.