Page images
PDF
EPUB

against the upper side of the flower. First a stamen on one side opens its anthers and exposes its pollen. The humble-bee, as it bustles in and out, brushes this off. Then another stamen exposes its pollen on the other side, then another and another; but not till all the pollen has been brushed off does the cleft-end of the pistil open, and expose its viscid stigma. The humblebee brushes off the pollen unto its hairy coat from the upper flowers of one raceme and carries it direct to the lowest flowers of another, where the viscid stigmas are open and ready to receive it. If the humble-bee went first to the upper flowers of the spike and proceeded downwards, the whole economy of this plant to procure cross fertilisation would be npset.* The open flower of the foxglove hangs downwards. The lower part, or dilated opening of the tube, is turned outwards, and has scattered stiff hairs distributed over its inner surface

e ; above these the inside of the flower hangs almost perpendicularly, and is smooth and pearly. The large humblebee bustles in with the greatest ease, and uses these hairs as footholds whilst he is sucking the honey; but the smaller honey-bees are impeded by them, and when, having at last struggled through them, they reach the pearly, slippery precipice above, they are completely baffled. I passed the autumn of 1857 in North Wales, where the foxglove was very abundant, and watched the flowers throughout the season, but only once saw

* Darwin mentions having seen humble-bees visiting the flowering spikes of the Spiranthes autumnalis (ladies' tresses), and notices that they always commenced with the bottom flowers, and crawling spirally up sucked one flower after the other, and shows how this proceeding ensures the cross fertilisation of different plants.—“Fertilisation of Orchids,” p. 127.

Ch. VIII.)

SPIDERS THE PREY OF WASPS.

133

a small bee reach the nectary, though many were seen trying in vain to do so.

Great attention has of late years been paid by naturalists to the wonderful contrivances amongst flowers to secure cross fertilisation; but the structure of many cannot, I believe, be understood, unless we take into consideration not only the beautiful adaptations for securing the services of the proper insect or bird, but also the contrivances for preventing insects that would not be useful, from obtaining access to the nectar. Thus the immense length of the nectary of the Angræcum sesquipedale of Madagascar might, perhaps, have been completely explained by Mr. Wallace, if this important purpose

had been taken into account.*

The tramway in some parts was on raised ground, in others excavated in the bank side. In the cuttings the nearly perpendicular clay slopes were frequented by many kinds of wasps that excavated round holes of the diameter of their own bodies, and stored them with sting-paralysed spiders, grasshoppers, or horse - flies. Amongst these they lay their eggs, and the white grubs that issue therefrom feed on the poor prisoners. I one day saw a small black and yellow banded wasp (Pompilus polistoides) hunting for spiders; it approached a web where a spider was stationed in the centre, made a dart towards it—apparently a feint to frighten the spider clear of its web; at any rate it had that effect, for it fell to the ground, and was immediately seized by the wasp, who stung it, then ran quickly backwards, dragging the spider after it, up a branch reaching to the

* “Natural Selection,” by A. R. Wallace, p. 272.

in

ground, until it got high enough, when it flew heavily off with it. It was so small, and the spider so heavy, that it probably could not have raised it from the ground by flight. All over the world there are wasps that store their nests with the bodies of spiders for their young to feed on. In Australia, I often witnessed a wasp combating with a large flat spider that is found on the bark of trees. It would fall to the ground, and lie on its back, so as to be able to grapple with its opponent; but the wasp was always the victor in the encounters I saw, although it was not always allowed to carry its prey off

peace. One day, sitting on the sand-banks on the coast of Hobson's Bay, I saw one dragging along a large spider. Three or four inches above it hovered two minute flies, keeping a little behind, and advancing with it. The wasp seemed much disturbed by the presence of the tiny flies, and twice left its prey to fly up towards them, but they darted away immediately, As soon as the wasp returned to the spider, there they were hovering over and following it again. At last, unable to drive away its small tormentors, the wasp reached its burrow and took down the spider, and the two flies stationed themselves one on each side the entrance, and would, doubtless, when the wasp went away to seek another victim, descend and lay their own eggs in the nest.

The variety of wasps, as of all other insects, was very great around Santo Domingo. Many made papery nests, hanging from the undersides of large leaves. Others hung their open cells underneath verandahs and eaves of houses. One large black one was particularly abundant about houses, and many people got stung by

Ch. VIII.]

INSTINCT AT FAULT.

135

them. They also build their pendent nests in the orange and lime trees, and it is not always safe to gather the fruit. Fortunately they are heavy flyers, and can often be struck down or evaded in their attacks. They do good where there are gardens, as they feed their young on caterpillars, and are continually hunting for them. Another species, banded brown and yellow (Polistes carnifex), has similar habits, but is not

Bates, in his account of the habits of the sand-wasps at Santarem, on the Amazon, gives an interesting account of the way in which they took a few turns in the air around the hole they had made in the sand, before leaving to seek for flies in the forest, apparently to mark well the position of the burrow, so that on their return they might find it without difficulty. He remarks that this precaution would be said to be instinctive, but that the instinct is no mysterious and unintelligible agent, but a mental process in each individnal differing from the same in man only by its unerring certainty.* I had an opportunity of confirming his account of the proceedings of wasps when quitting a locality to which they wished to return, in all but their unerring certainty. I could not help noting how similar they were to the way in which a man would act who wished to return to some spot not easily found out, and with which he was not previously acquainted. A specimen of the Polistes carnifex was hunting about for caterpillars in my garden. I found one about an inch long, and held it out towards the wasp on the point of a stick. The wasp seized the caterpillar immediately, and commenced biting it from head to tail, soon reducing the soft body to a mass of pulp. Then rolling up about one-half of the pulp into a ball, it carried it off. Being at the time amidst a thick mass of a fine-leaved climbing plant, it proceeded, before flying away, to take note of the place where the other half was left. To do this, it hovered in front for a few seconds, then took small circles in front, then larger ones round the whole plant. I thought it had gone, but it returned again, and had another look at the opening in the dense foliage down which the other half of the caterpillar lay. It then flew away, but must bave left its burden for distribution with its comrades at the nest, for it returned in less than two minutes, and making one circle around the bush, descended to the opening, alighted on a leaf, and ran inside. The green remnant of the caterpillar was lying on another leaf inside, but not connected with the one on which the wasp alighted, so that in running in it missed the object and soon got hopelessly lost in the thick foliage. Coming out, it took another circle, and pounced down on the same spot again, as soon as it came opposite to it. Three small seed - pods, which here grew close together, formed the marks that I had myself taken to note the place, and these the wasp seemed also to have taken as its guide, for it flew directly down to them, and ran inside ; but the small leaf on which the fragment of caterpillar lay, not being directly connected with any on the outside, it again missed it, and again got far away from the object of its search. It then thew out again, and the same process was repeated again and again. Always when in circling round it came in sight of the seed-pods down it pounced, alighted near them, and recommenced its quest on foot. I was surprised at

So common.

* “Naturalist on the Amazon,” p. 222.

« EelmineJätka »