Part 5

There really seems to be scarcely any genus of insect that is not seized upon by one or other of these burrowers, and packed away in a half living state to form food for their young. There is one of these solitary burrowing wasps called the Astata boops, deriving its specific name from its large round eyes, which in the male completely unite at the back of the head. The abdomen is shaped something like a boy's peg-top, or a symmetrical turnip, the peg of the top, or the point of the turnip, corresponding to the top of the abdomen. Its length is about half an inch, and its colour is black, with a rust-red patch on the end of the abdomen.

There is a remarkably pretty, and very variable, sand-wasp, which is plentiful in most parts of the country. The colour is black, and the abdomen is banded by four yellow bars. Its feet are also yellow. Mr. Smith has written a very interesting account of the proceedings of this insect.

"Having frequently observed the habits of the type of this genus, Mellinus arvensis, and reared it from the larva state, a few observations are here recorded. When the parent insect has formed a burrow of the required length, and enlarged the extremity into a chamber of proper dimensions, she issues forth in search of the proper nutriment for her young; this consists of various dipterous insects: species of various genera are equally adapted to her purpose--Muscidæ, Syrphidæ, &c., are captured.

"It is amusing to see four or five females lie in wait upon a patch of cow-dung until some luckless fly settles on it. When this happens, a cunning and gradual approach is made; a sudden attempt would not succeed. The fly is the insect of quickest flight, therefore a degree of intrigue is necessary. This is managed by running past the victim slowly, and apparently in an unconcerned manner, until the poor fly is caught unawares, and carried off by the Mellinus to its burrow. The first fly being deposited, an egg is laid. The necessary number of flies are soon secured, and her task is completed. Sometimes she is interrupted by rainy weather, and it is some days ere she can store up the quantity required.

"A larva found feeding became full-fed in ten days. Six flies were devoured, the heads, harder parts of the throat, portions of the abdomen, and the legs, being left untouched. The larva spins a tough, thin, brown silken cocoon, passes the winter and spring in the larva state, changes to the nymph on the approach of summer, and appears about the beginning of autumn in the perfect state."

There is a genus of hymenopterous insects known by the name of Scolia, which are remarkable for their fossorial powers. The species represented in the engraving is called Scolia Xantiana, and is a native of California.

When the female Scolia is about to fulfil the great object for which she came into the world, she looks about for a suitable spot, where the ground is not too hard, and digs a perpendicular burrow of some depth, enlarging it at the bottom, and digging horizontally, so that the general shape of the burrow somewhat resembles that of a boot. When the burrow is completed, the insect flies off in search of food for its young, and presently returns, bearing with her a grub, which she clasps tightly under her chest, so that her wings may be at liberty. She then takes the grub to the bottom of the tunnel, deposits an egg upon it, and if the grub be a small one, goes off to fetch another. When a sufficiency of food has been obtained, she covers up the grub and egg and leaves the latter to its fate. In due time it is hatched, and begins straightway to feed upon its unfortunate fellow-prisoner. When all the food is gone, it is old enough to assume the perfect form, and when it finally becomes a perfect insect, it makes its way into the open air, and straightway looks out for a mate.

An European species of this genus, which is called Scolia flavifrons, is remarkable for the four large, round spots on the upper surface of the abdomen. This species always feeds its young on the grub of a beetle, one of the lamellicorn group, and in this case the grub is so large that one is sufficient.

In the illustration, the left hand figure shows a section of the burrow of Scolia Xantiana, and exhibits the enlarged portion of the tunnel in which are placed the young Scolia and the unfortunate grub which has to serve it for food. The insect itself is seen in the centre.

For figures 3 and 4 the reader is referred to the heading "Spiders."

There is another British insect which feeds its young with flies, and which catches them in a manner somewhat similar to that which has recently been narrated when treating of the Mellinus. The insect in question is called Oxybelus unuglumis, and is a very pretty species. Its length is seldom much more than a quarter of an inch, and its colour is black, with some silvery hair about the face, and with some spots and bands of white, more or less yellowish, upon the pointed abdomen. The male is usually smaller than the female, but compensates for this want of size by his more brilliant colouring.

Mr. F. Smith has described to me the method employed by this insect in catching flies. In the air it would not have a chance of success, and so it proceeds after a fashion very much like that which is adopted by the hunting-spider. Choosing some spot where flies are likely to settle, such as a bare, sunny bank, the Oxybelus alights upon it and begins to run about without any apparent motive. At first the flies are rather alarmed, but after a while they become accustomed to the rapid movements of their foe, and allow it to come nearer and nearer the cause of its perambulations. As soon as it has succeeded in drawing within a few inches of a fly, the Oxybelus leaps upon it, just like the hunting spider on its prey, and flies off before the victim knows that an attack is even meditated.

The burrow of this species is made in hard white sand.

Several species of the genus Cerceris are noted, not only as burrowers, but for the exceeding variety of the food which they store in their dwellings. The most common species, Cerceris arenaria, makes its tunnel in hard, sandy spots, and is usually to be found about the middle of July and August. The length of this insect rather exceeds half an inch, and its colour is black, profusely spotted and barred with yellow. It is rather slenderly made, and gives little external indications of the great strength which it possesses.

This insect prefers to stock its nest with weevils of different kinds--a most singular choice, when the hardness of the exterior is taken into consideration. The well-known nut-weevil (Balaninus nucum), with its hard, round body, and long mouth, is frequently taken by this species of Cerceris, and Mr. Smith further mentions that he has captured it in the act of taking the weevil called Otiorhynchus sulcatus to its nest.

This beetle is among the most noxious of our garden foes, and the more so because its ravages are unseen. In its larval state it infests the roots of many of our succulent plants and flowers, and has a habit of eating away the plant just at the junction of the root and stem. Even flowers in pots are apt to be infested by this insect, and often die without the cause of their death being discovered. It is about half an inch in length, white, and is destitute of feet, their office being performed by bundles of stiff hairs, which are dispersed round the body.

In its perfect state it is about the third of an inch in length, the colour is black, covered with a coating of very fine and short grey hairs, and along its back are a number of short longitudinal grooves. From this latter circumstance it derives its name of "sulcatus," or grooved.

The exterior of this beetle is extremely hard, even exceptionally so among the hard-bodied weevils. It is extremely difficult to get a pin through the body, and the entomologist is often obliged to bore a hole with a stout needle before the pin can be inserted. Yet, the Cerceris uses this insect as the food of its young, and stores them away in its burrow. That the young should eat them seems as impossible as if a lobster or a box-tortoise had been inserted in their place. It is, however, thought by most practical entomologists that the shell of the weevil is softened by lying in the damp ground, and that as the young is not hatched for several days after the burrow is sealed up, the hard wing cases have time to soften.

Another species of the same genus, Cerceris interrupta, has the curious habit of making its burrow in the hardest ground which it can penetrate, and is generally to be found in well used footpaths. This species also uses weevils for the food of its young, but prefers those small weevils which are classed under the genus Apion, and which are readily known by their pear-shaped bodies and rather elongated heads. [There are about seventy species of Apion, so that the Cerceris has plenty of choice.]

Mason-Bees.

It would not be easy to find a more simple, and, at the same time, ingenious specimen of insect architecture than the nests of those species of solitary bees which have been justly called mason-bees (Megachile, Latreille). Réaumur, who was struck by the analogies between the proceedings of insects and human arts, first gave to bees, wasps, and caterpillars those names which indicate the character of their labours; and which, though they may be considered a little fanciful, are at least calculated to arrest the attention. The nests of mason-bees are constructed of various materials; some with sand, some with earth mixed with chalk, and some with a mixture of earthy substances and wood.

On the north-east wall of Greenwich Park, facing the road, and about four feet from the ground, we discovered (J. R.), December 10th, 1828, the nest of a mason-bee, formed in the perpendicular line of cement between two bricks. Externally there was an irregular cake of dry mud, precisely as if a handful of wet road-stuff had been taken from a cart-rut and thrown against the wall; though, upon closer inspection, the cake contained more small stones than usually occur in the mud of the adjacent cart-ruts. We should in fact have passed it by without notice had there not been a circular hole on one side of it, indicating the perforation of some insect. This hole was found to be the orifice of a cell about an inch deep, exactly of the form and size of a lady's thimble, finely polished, and of the colour of plaster-of-paris, but stained in various places with yellow.

This cell was empty; but, upon removing the cake of mud, we discovered another cell, separated from the former by a partition about a quarter of an inch thick, and in it a living bee, from which the preceding figure was drawn, and which, as we supposed, had just changed from the pupa to the winged state, in consequence of the uncommon mildness of the weather. The one which had occupied the adjacent cell had no doubt already dug its way out of its prison, and would probably fall a victim to the first frost.

Our nest contained only two cells--perhaps from there not being room between the bricks for more.

This species is notable for the many parasites who infect the habitation and destroy the inmates. Perhaps the very worst and most destructive of these parasites is the common earwig, which wreaks wholesale desolation in the nest. It creeps into the burrow, and if it finds a store of pollen laid up for the young, it will eat the pollen. But if the young grub be hatched it will eat the grub. If the inmate be in the pupal state, or even if it be ready to emerge in its perfect condition, the earwig will eat it.

There are two bees which are parasitic upon this unfortunate insect, both belonging the genus Melecta.

But the most destructive of these parasites appears to be an insect which belongs to the great family of Chalcididæ. These insects are of the hymenopterous order, are of very minute dimensions, and of the most brilliant colours. Indeed, if they were an inch or two in length, instead of the eighth or twelfth of an inch, they would not suffer in comparison with the most gorgeous inhabitants of tropical countries.

Their forms are most eccentric, some species having the abdomen small and round and set on a long footstalk, while others have that portion of the body placed so closely against the thorax, that the short footstalk is scarcely visible. Others have certain joints of the legs so large that a single joint equals the entire abdomen. Some have the ovipositor projecting boldly from the body, while others have it tucked up underneath, and others again have it quite short. But there is one point which distinguishes them all, namely, the almost veinless character of the wings.