Sphex coeruleus is frequently stated to have the habit of provisioning its nests with both Orthoptera and Spiders; but Kohl considers with reason that this record is, as regards spiders, a mistake, arising probably from a confusion with some other Insect of similar appearance, such as Pelopaeus (Sceliphron) coeruleus. S. coeruleus is no doubt the same as S. (Chlorion) lobatus, which Rothney observed in East India, provisioning its nests with Orthoptera. He discovered a nest in process of construction, and during the absence of the mother-wasp abstracted from the burrow a large field-cricket that she had placed in it; he then deposited the Orthopteron near the cell; the parent Sphex on returning to work entered the tunnel and found the provision placed therein had disappeared; she came out in a state of excitement, looked for the missing cricket, soon discovered it, submitted it to the process of malaxation or kneading, and again placed it in the nest, after having cleared it from some ants that had commenced to infest it. She then disappeared, and Rothney repeated the experiment; in due course the same series of operations was performed, and were repeated many times, the Sphex evidently acting in each case as if either the cricket had disappeared owing to its being incompletely stunned, or to its having been stolen by ants. Finally, the observer placed the cricket at a greater distance from the nest, when it recovered from the ill-treatment it had received sufficiently to make its escape. The points of interest in this account are the fact that the cricket was only temporarily paralysed, and that the wasp was quite able to cope with the two special difficulties that must frequently occur to the species in its usual round of occupations.
The genus Ammophila is of wide distribution, and its species make vertical tunnels in the ground. The habits of some of the species found in France have been described by Fabre. The Insect does not inhabit the burrow while it is in process of formation, but quits it; and some of the species temporarily close the entry to the incomplete nest with a stone. The tunnel is a simple shaft with a single cell at its termination; this is stored with caterpillars, the different species of Ammophila selecting different grubs for the purpose. A. hirsuta hibernates in the perfect state, and carries on its work in the spring; it chooses a single larva of considerable size belonging to one of the nocturnal Lepidoptera, and this it paralyses by a series of about nine stings, of which one is implanted in each segment from the first thoracic ring backwards; it forms the burrow only after the food to be placed therein has been obtained. The caterpillar used is subterranean in habit, and the Ammophila detects the larva by some sense, the nature of which appears at present quite uncertain. A. holosericea chooses smaller larvae of the family Geometridae, and uses only one or two stingings to paralyse each larva; several caterpillars are used to provision a single cell, and they are often selected of different colours.
Marchal has also published an important account of the proceedings of A. affinis; he confirms Fabre's observations, and even adds to their interest by suggesting that the Ammophila administers special stings for the purpose of paralysing the mandibles of the caterpillar and depriving it of any power of afterwards injuring the larva that will feed on it. He thinks the mother-Ammophila herself profits by appropriating an exudation from the victim.
Some species of Sphegides have the curious habit of choosing the interiors of human habitations as the spots most suitable for the formation of their own domestic establishments. Fabre has given a charming account of the habits of Pelopaeus (Sceliphron) spirifex, a species that inhabits the South of Europe, and that forms its nests in the cottages of the peasants. The spot usually selected is a nook in the broad, open fireplace, out of reach of the flames, though not of the smoke; here the Pelopaeus forms a nest of earth, consisting of ten to fifty cells, the material being mud or clay brought in little balls by the aid of the Insect's mandibles; about twenty visits are required in order to complete one cell, so that for the construction of a large nest of fifty cells, about one thousand visits must be made by the Insect. It flies in and out of the house apparently not at all incommoded by the human habitants, or by the fact that the peasant's potage may be simmering on the fire quite close to where the fearless little creature is carrying on its architectural operations. The cells are stored with spiders, of which the wasp has to bring a plentiful supply, so that its operations extend over a considerable period. The prey is captured by the Pelopaeus whilst on the wing, and carried off at once, being probably stung by the wasp during the process of transit; apparently it is killed by the operation, not merely paralysed. Only small spiders are taken by this species, and the larva of the Pelopaeus consumes them in a short time, one by one, before the process of decomposition sets in; the egg, too, is laid on the first spider introduced, and this is of course at the bottom of the cell, so that the spiders are eaten by the wasp's larva in the order in which they were brought to the cell. The cell is sealed up when full, the number of spiders placed in it being on the average about eight. The larva completes its task of consuming the store in about ten days, and then forms a cocoon for its metamorphosis. Two or three generations are produced in a single year, the autumnal one passing eight or nine months in the clay cells, which are lodged in a nook of the peasant's hearth, and exposed to the smoke of his fire during all the months of winter. Pelopaeus (Sceliphron) is a genus including many species;[[51]] several of them are known to be specially attached to the habitations of human beings. Roth has given an account of the habits of P. (Sceliphron) laetus in Australia; he says that in some parts it is very difficult to keep these wasps out of the houses; the nest is formed of mud, and constructed on the furniture or in any part of a room that suits the fancy of the Insect. This it must be admitted is, according to human ideas, liable to the charge of being very capricious. Roth timed a wasp building its nest, and found that it brought a fresh load of mud every two or three minutes. If the wasp be allowed to complete the nest undisturbed, she does so by adding to the exterior diagonal streaks of mud, so giving to the nest the look of a small piece of the bark of a common acacia. The construction consists of from ten to twenty cells, and when completed is provisioned with spiders for the use of the young. This wasp is much pestered by parasites, some of which prevent the development of the larvae by consuming the spiders intended by the mother-wasp for its young. A fly, of the Order Diptera, is said to follow the wasp when carrying a spider, and to deposit also an egg on the food; as the Dipterous larvae have more rapid powers of assimilation, the Pelopaeus larvae are starved to death; and their mildewed remains may be found in the cell, after their enemies have become fully developed and have flown away. Another parasite is said to eat the wasp-larva, and attains this end by introducing an egg through the mud wall and the cocoon of the wasp—a habit that seems to indicate a Leucospid parasite. Tachytes australis, a wasp of the sub-family Larrides also dispossesses this Pelopaeus in a manner we shall subsequently describe. This fragment of natural history from Australia has a special interest, for we find repeated there similar complex biological relations to those existing in the case of the European congeners.
P. (Sceliphron) madraspatanus is common in the north-west provinces of Hindostan, and is called the "mud-dauber" by the European residents. According to Horne it constructs its cells in the oddest places, but chiefly about the inhabited apartments in houses. It is perfectly fearless when engaged in building: the cells are four to six in number, and are usually provisioned with spiders to the number of about twenty. On one occasion it was observed that green caterpillars were stored instead of spiders. The species is said to be protected by a peculiar odour as well as by its sting; it is also stated that it disguises its edifice when completed by making it look like a dab of mud, and on one occasion "rays of mud were observed round the nest, even more exactly imitating a lump of mud thrown with some force." P. (Sceliphron) bilineatus, formerly thought to be a variety of P. madraspatanus, builds its nests in hedges and trees.
Sub-Fam. 2. Ampulicides.—Prothorax long and narrow, forming a neck in front; clypeus beak-like; four submarginal cells, the outer one being complete; metathorax elongate, the posterior part of the metasternum deeply divided to allow a perfect inflection of the abdomen.
Fig. 44—Ampulex compressa. Male. East India.
This is one of the smallest of the divisions of the Sphegidae, but has a very wide distribution, being represented in both the Eastern and Western Hemispheres. It is allied to the Sphegides, but differs by the prolongation of the neck and of the head, and by the articulation between the petiole and thorax being placed on the under surface of the body; the wing-nervures are said to be of inferior importance owing to their frequently differing in individuals of the same species. These Insects appear to be rare in individuals, as well as few in species, and but little has been recorded as to their habits; but it is known that they live on cockroaches. Perkins has given a brief sketch of the habits of Ampulex sibirica that is of great interest, but requires confirmation. He says that this Insect, in West Africa, enters apartments where cockroaches abound, and attacking one, that may probably be four times its own size, succeeds, after a struggle, in stinging it; the cockroach instantly becomes quiet and submissive, and suffers itself to be led away and placed in confinement in some spot such as a keyhole, and in one case was apparently prevented from afterwards escaping, by the wasp carrying some heavy nails into the keyhole. The larva of the Ampulex may be presumed to live on the Blattid, as it is added that dead bodies of the cockroaches are frequently found with the empty cocoon protruding from them. This account, if correct, points to some features in the habits of this Insect that are unique. A remark made by Rothney in reference to the habits of A. (Rhinopsis) ruficornis seems to indicate some similar instinct on the part of that species; he says, "I also saw two or three of these wasps collar a peculiar cockroach by the antennae and lead it off into a crack in the bark, but as the cockroach reappeared smiling each time, I don't know what was up." The same observer records that this species associates with Sima rufonigra, an ant it greatly resembles in appearance, as well as with a spider that is also of similar appearance (Fig. 72). Schurr has given a brief account of the proceedings of Ampulex compressa, and his statements also tend to confirm the correctness of Perkins' report. The habits of a species of Ampulex were partially known to Réaumur, who described them on the authority of M. Cossigni. The species is believed to be A. compressa, which occurs not only in East India, but also in the island of Bourbon, the locality where M. Cossigni made his observation: his account is, like the others, a mere sketch of certain points observed, the most important of which is that when Ampulex cannot introduce the cockroach into a hole that it has selected as suitable, it bites off some portions of the body in order to reduce the poor Insect to the necessary extent.
From these fragmentary observations it would appear that the sting of the Ampulex has not so powerful a paralysing effect as that of most other Fossores; and that the Ampulex does not form any nest, but takes advantage of suitable holes and crevices to store the victim in; also that it displays considerable ingenuity in the selection of materials with which to block up the cavity in which it has placed the partially incapacitated creature.