There are many animals which either habitually or occasionally feed upon spiders. They are the staple food of some hummingbirds, and many other birds appear to find in them a pleasing variation on their customary insect diet. These creatures, moreover, are destructive to spiders in another way, by stealing the material of their webs, and especially the more closely textured silk of their egg-cocoons, to aid in the construction of their nests. M‘Cook has observed this habit in the case of Vireo noveborocensis, and he states, on the authority of others, that the “Plover” and the “Wren” are addicted to it. The smaller species of monkeys are extremely fond of spiders, and devour large numbers of them. They are said, moreover, to take a mischievous delight in pulling them in pieces. Armadillos, ant-eaters, snakes, lizards, and indeed all animals of insectivorous habit, draw no distinction between Insecta and Arachnida, but feed upon both indiscriminately. The army ants, so destructive to insect life in tropical countries, include spiders among their victims. These formidable insects march along in vast hordes, swarming over and tearing in pieces any small animal which lies in their path. They climb over intervening obstacles, searching every cranny, and stripping them bare of animal life. Insects which attempt to save themselves by flight are preyed upon by the birds, which are always to be seen hovering above the advancing army. The spider’s only resource is to hang from its thread in mid-air beneath the branch over which the ants are swarming, for the spider line is impracticable to the ant. Belt[[294]] has observed a spider escape the general destruction by this means.
Protective Coloration.—Examples are numerous in which the spider relies upon the inconspicuousness not of its nest, but of itself, to escape its natural foes. Its general hues and markings are either such as to render it not readily distinguishable among its ordinary surroundings, or the principle has been carried still further, and a special object has been “mimicked” with more or less fidelity.
This country is not rich in the more striking mimetic forms, but the observer cannot fail to notice a very general correspondence in hue between the spiders of various habits of life and their environment. Those which run on the ground are usually dull-coloured; tree-living species affect grey and green tints, and those which hunt their food amongst sand and stones are frequently so mottled with yellow, red, and grey, that they can scarcely be recognised except when in motion.
A few of our indigenous species may be mentioned as especially protected by their colour and conformation. Tibellus oblongus is a straw-coloured spider with an elongated body, which lives among dry grass and rushes. When alarmed it clings closely to a dry stem, remains motionless, and escapes observation by its peculiarity of colour and shape. Misumena vatia, another of the Thomisidae or Crab-spiders, approximates in colour to the flowers in which it is accustomed to lurk on the watch for prey. It is of a variable hue, generally yellow or pink, and some observers believe that they have seen it gently waving its anterior legs in a way which made them easily mistaken for the stamens of the flower stirred by the breeze. Its purpose appears to be to deceive, not its enemies, but its victims. It seems to be partial to the blooms of the great mullein (Verbascum thapsus), and Pickard-Cambridge has more than once seen it seize and overcome a bee which had visited the flower in search of honey. He has also observed it in the blossoms of rose and furze bushes.[[295]]
An Epeirid (Tetragnatha extensa) resembles Tibellus in its method of concealing itself when alarmed. It also possesses an elongated abdomen, of a grey-green tint, which it closely applies to one of the twigs among which it has stretched its net, at the same time extending its four long anterior legs straight before it, and in this position it lies perdu, and is very easily overlooked. Another Orb-weaver, Epeira cucurbitina, is of an apple-green colour, which is admirably calculated to conceal it among the leaves which surround its snare.
Most of our English Attidae, or Jumping-spiders, imitate closely the prevailing tone of the surfaces on which they are accustomed to hunt. This will be recognised in the familiar striped Wall-spider, Salticus scenicus, and we may also mention the grey Attus pubescens, which affects stone walls, and the speckled Attus saltator, which is hardly distinguishable from the sand which it searches for food.
Examples may also be found among the Lycosidae or Wolf-spiders. Of the prettily variegated Lycosa picta, Pickard-Cambridge says: “Much variation exists in the extent of the different portions of the pattern and in their depth of colouring, these often taking their prevailing tint from the colour of the soil in which the spider is found. The best marked, richest coloured, and largest examples are found on sandy and gravelly heaths, where there is considerable depth and variety of colouring.... But on the uniformly tinted greyish-yellow sandhills between Poole and Christchurch I have found a dwarf, pale yellow-brown variety, with scarcely any dark markings on it at all, the legs being of a uniform hue, and wholly destitute of dark annuli.”[[296]]
Mimicry.—In the island of Portland, a locality remarkable for the number of species peculiar to itself, there is found a spider, Micaria scintillans, very closely resembling a large blackish ant which frequents the same neighbourhood. Its movements, moreover, are exceedingly ant-like, as it hurries along in a zigzag course, frequently running up and down grass stems after the manner of those insects. It is a great lover of sunshine, and disappears as soon as the sun is obscured by a passing cloud.
Such resemblances, obvious enough in nature, and heightened by the behaviour of the mimetic form, are often by no means striking in the cabinet. In some American species of spiders, however, imitation of the ant has passed beyond the stage of a general resemblance as regards size and colour and method of progression. The head of the ant is well marked off from the body, and the thorax is frequently divided into distinct regions. These peculiarities are imitated by constrictions in the cephalothorax of mimetic spiders. The resemblance, moreover, is much increased by their habit of using but six legs for locomotion, and carrying the second pair as ants do their antennae. The best known examples of these spiders are Synageles picata and Synemosyna formica (see Fig. [215], C, p. 420), and even more striking resemblances have been observed among some undescribed South American species.
The object of such mimicry seems to vary in different cases. Sometimes the spider preys upon the ant which it resembles. Sometimes, again, by its disguise, it escapes the notice of the ant which would otherwise feed upon it. More often spider and ant are neutral as regards each other, but, under cover of its resemblance, the Arachnid is enabled to approach an unsuspecting victim to which the ant is not a terror. Again, the unpleasantly acid taste of ants is unpalatable to most birds, though not to all, and the increased danger from specially ant-eating birds may be more than counterbalanced by the immunity they acquire from other birds.