XXXVII.—Insect Architecture, or notes on the habits of the Black Spider-wasp, of New Zealand.
[Read before the Wellington Philosophical Society, 11th November, 1876.]
Among the Hymenoptera in New Zealand, the Pompilidæ are represented by two recorded species—Pompilus fugax and P. monarchus; but, as the descriptions are not at present accessible here, I cannot say with any certainty to which of these species (if either) the specimen which I exhibit this evening is referable. My. object, however, in bringing the subject under the notice of this meeting, is not so much the identification of the species, which will follow in due course, but rather to call attention to some very interesting facts in the natural history of this Native Wasp, and more particularly as bearing on the study of insect architecture.
In his remarks on the Hymenoptera, Kirby says: “The functions which are given in charge to the several members of this Order are various. Some, like the predaceous and carnivorous tribes of the Diptera, appear engaged in perpetual warfare with other insects; thus the wasps and hornets seize flies of every kind that come in their way, and will even attack the meat in the shambles; the Caterpillar-wasp (Ammophila) walks off with caterpillars, the Spider-wasp (Pompilus) with spiders, and the Flywasp (Bembex) with flies. But the motive that influences them will furnish an excuse for their predatory habits. They do not commit these acts of violence to gratify their own thirst for blood, like many of the flies, but to furnish their young with food suited to their natures. The wasp carries the pieces of flesh she steals from the butcher to the young grubs in the cells of her paper mansion. The other wasps. I have mentioned each commit their eggs to the animal they are taught to select, and then bury it; so that the young grub, when hatched, may revel in plenty.”*
The family Pompilidœ, or Spider-wasps, of which about 700 species are known, have a wide geographical range, extending from the temperate regions to the tropics, the genus Pompilus alone containing some 500 recorded forms. The whole group, it would appear, are parasitic in their habits, and, in depositing their eggs in their skilfully-constructed cells, they take care to lay up a store of spiders' bodies by way of provision for a future family. The manner of doing this will be presently described.
[Footnote] * “History, Habits, and Instincts of Animals,” p.241.
The Black Spider-wasp of New Zealand, like many of its congeners, is an accomplished builder in clay. On this account it is generally known as the “Mason Bee;” but this name is wrongly applied, inasmuch as the Mason Bees (Osmia) form a very distinct section of themselves. They also construct clay houses with much skill and ingenuity, or form tunnels and burrows underground, but, like true and orthodox bees, they lay up a supply of pollen or honey in their cells for the nourishment of their larvæ.
The nest which I have now the honor to place before the Society, and a vertical section of which is shown in the accompanying sketch (Fig. 1, Plate III), is a fair sample of the way in which the Black Spider-wasp constructs a habitation for her family. The masonry is firm and compact, the walls as well as the interior partitions, dividing one cell from another, being formed of yellow clay, which hardens by exposure to the atmosphere. The exterior surface is finely corrugated, or covered with minute striæ, presenting a vermiculated appearance; and the whole structure, before being closed up and hermetically sealed, is very neatly finished. On opening the nest by making a longitudinal cutting, it is found that each cell, which is complstely shut off from the adjoining ones, contains one or more spiders, not lifeless but apparently in a state of unconscious torpor, and performing their last offices in the economy of insect-life, which is patiently to await the hatching of the parsitic grub, and then to supply the larder with their own bodies. I have not been able to watch the hatching operations of this insect; but, judging from what we know of its allies, we may, I think, conclude that the Spider-wasp deposits its egg in or upon the body of its victim; that the larva hatches out in due time, and then feeds on the spider till it has attained its full size, when it spins itself a thin integument, or cocoon, and remains in an inactive state until the following Spring, when it completes its transformations.
In the specimen of the nest now exhibited, the cocoon stage has been reached, and of the original spider-stores nothing is left but the shrivelled remains. This nest was taken on the last day of October, from the outer wall of a house on Wellington Terrace. It was found, among many others, in the wall-chinks, behind a verandah-panel, the situation having become exposed in the course of necessary repairs to the building. The cocoons are sometimes oval, sometimes elliptical in form, and of a yellowish-brown colour.
The spiders captured and stored in the manner mentioned are not killed, but are rendered insensible by the injection of some occult poison from the body of the Wasp. The sting of the insect appears to penetrate the nervous centres, and to paralyze the victim without depriving it of life, so that it may exist in a comatose or torpid state for many weeks, or till required to
furnish living food for the future grub. Caterpillars, after being stung by the Caterpillar-wasp (Ammophila)〉, will transform into chrysalids, though too weak to change into moths. A writer in South Africa, Mr. Gueinzins, observes that “large spiders and caterpillars become immediately motionless on being stung; and I cannot help thinking that the poisonous acid of Hymenoptera has an antiseptic and preserving property; for caterpillars and locusts retain their colours weeks after being stung, and this, too, in a moist situation under a burning sun.” So potent is this animal poison, that it enables another member of the same group, Pompilus formosus, which inhabits Texas, to paralyze with a single sting that immense Tarantula, the Mygale hentzii, known as the Bird-killer. Having inserted its egg in the body of this hugo spider, it proceeds to bury it in a nest dug out of the ground to the depth of five or six inches. There is a tropical species belonging to the genus Ampulex, which inhabits Zanzibar, and oviposits in the body of the cockroach; and the dead bodies of the cockroaches are often found with the empty cocoon of the Wasp occupying the cavity of the abdomen. An observer, who has watched the attacks of this Wasp, writes:—“The cockroach, as if cowed at its presence, immediately yields without a struggle. The Ampulex stings and paralyzes its victim, and then flies away with it.”
Like many of the allied species, our Black Spider-wasp, whilst engaged in nest-building, and likewise when manipulating the spiders, emits a continuous buzzing sound, similar to that of a large house-fly entangled in a web. In its other habits, I am not aware that it differs in any respect from its congeners, Like the Pompilus formosus, or Tarantula-killer, just mentioned, it appears to feed upon the honey and pollen of native flowers, and its favourite nourishment is taken from the fragrant blossoms of the Kahikatoa (Leptospermum scoparium), or tea-tree scrub of the colonists.
The following communication, under the head of “Notes on the Mason Bee,” was made to the Auckland Institute, by Major Mair, R.M., on the 14th June, 1875, and I have obtained his permission to embody it here. I ought to add, however, that Major Mair expressed a doubt as to whether he was right in designating the insect a Mason Bee:—
“The accompanying account, clipped from a newspaper, agrees to some extent with my own experience of the habits of this insect, but here they confine their nests to wood-work. I first observed them building in my verandah in December last, and now (April 17th) they are still at work. Numbers of nests have been made in the crevices between the shingles and under the edges of the weather-boarding. In two instances, auger-holes in the wall-plates have been utilized. The latter have been broken and rescaled several times. I have seen nests four inches long, with a diameter of three-
quarters of an inch, containing six cells in a single row; but they are seldom found in places from which they can be easily removed, and are so fragile, that, after many attempts, I have only succeeded in getting one nest in anything like good preservation. I have not seen any with the cells in pairs. Upon opening a nest, the grub (one in each cell) may be found half coiled round the body of a spider which it is devouring. These spiders, though apparently lifeless, are not dead. The old nests contain the heads and legs of spiders, but in no instance have I met with any other insect in them. I can hardly believe that this remarkably fly is indigenous, though it may be closely allied to the one that captures small insects promiscuously and buries them in the ground, I suppose for the same purpose:—
“Last summer, a correspondent at Marton drew attention to a fly which attacked, and apparently killed spiders; and another, who seemed to know the insect, stated it to be an Ichneumon fly. This year they are not so numerous; but ample opportunities have been afforded for observing their habits, and it appears that they have also the character of Mason Bees, or Wasps. They construct nests consisting of a double row of cells, each of which is about a quarter of an inch in diameter, and half an inch deep. These cells are composed of clay, which the fly collects; and while forming them it emits a shrill sound like that of a blowfly entangled in a spider's web. As soon as a couple of cells are completed, the fly crams each of them full of spiders, alive, but apparently paralysed, and along with them, or in one of them, deposits an egg, which in a short time becomes a grub, resembling a bee or wasp grub, that devours the spiders. As the cells are filled, they are closed with clay, which forms the bottom of a second pair, and so the process goes on till a nest several inches long is formed and stocked with its living inmates. The nests are built against the angles of ceilings, rafters of verandahs, and other sheltered places, and a favourite situation seems to be the folds of a cloth, or other similar articles. In some houses as many as a dozen or more such nests have been destroyed this summer; and a survey-party working a few miles inland, have been quite annoyed by the insects, three or four nests per day having been built in the spare garments of the party, or in the folds of the bag which held their bedding and provisions. The fly is of a dark grey colour, almost black, and about the size of an ordinary bee, but rather longer and thinner. The walls of the cells are about a sixteenth of an inch thick, so that the insect, which, after devouring its stock of food, no doubt changes from a grub into a chrysalis, and thence into a perfect fly, will have no difficulty in breaking out of its prison. The fly is indigenous, but from some cause evidently on the increase, and seems quite harmless to anything but spiders.”
On the same subject, Captain Gilbert Mair has lately furnished me with the following notes:—
“In January, of the present year, a Mason-wasp commenced building its nest inside a small hut at Tauranga. It plastered it obliquely on the inner partition above a bedstead. When the door was closed, the Wasp made its ingress through a small hole in the window every few minutes, loaded with a little ball of damp mud which it carried in its feelers, all the time making a loud buzzing noise. It continued its building operations till the end of March, when the nest, which consisted of a single row of cells, had reached a length of sixteen inches. It was round on the outer surface, three-quarters of an inch in diameter, and marked with longitudinal stripes. It contained twenty separate cells, in each of which were a number of small brown spiders in a torpid state, and one or more of the Wasp's eggs. Upon the completion of each cell, the Wasp flew to a paling-fence, over which it hovered in search of a victim, on capturing which it immediately pierced it in the back. It might then be seen proceeding, tail-first, in the direction of the house, tugging lustily a spider more than its own weight, which it would drag along the ground, up the side of the house, and through the aperture to its nest, in spite of every obstacle. Unfortunately, the nest was knocked down and broken into many pieces. The spiders were still alive, though they had been imprisoned for several months. I believe this insect to be indigenous to New Zealand, for I observed some capturing spiders in a similar manner in 1857, but they appeared larger, and were of a more brilliant black than the attenuated specimens now in the Museum.”
I feel no doubt myself that the species is indigenous, being quite familiar with it in this district, and having, I believe, met with it in the North more than twenty years ago. But, for some unexplained reason, it makes a sudden appearance in great numbers at one season, and becomes scarce in the next, as though its occurrence were determined by fitful or irregular migrations from one part of the country to another. Major Mair, in writing to me only a few weeks ago, says he does not remember seeing many of them last summer, although they were so very abundant the year before. This summer, again, they are as numerous as ever in the Waikato.
Fig. 2, Plate III., in the accompanying sketch, represents the outer surface of the Spider-wasp's clay nest.