The majority of them are very small, more or less black, Theridiid spiders, the “micros” of the tribe, and their proper home is among the roots of grass and herbage. Many of these are interesting objects for the microscope—especially if males—because of the remarkable protuberances or turrets which rise from their heads and bear their eyes as on a watch tower.
These spiders are clearly not “out” for food; they have left their ordinary beat for quite another purpose, and we shall probably not have to wait long before discovering it. Some one of the group ceases its apparently purposeless wandering, and, turning its head in the direction of what slight wind there is, raises its fore-body to the full extent of its straightened legs, and elevates its abdomen to the utmost. Now watch closely—using a handglass if you have one—and you will see streamers of silk proceeding from its spinnerets. They are shot out for a short distance and then the air current draws them out further till they often extend for several feet, though their extreme fineness makes it almost impossible to form an accurate judgment of their length. Meanwhile the spider has not merely been standing on its “toes,”—it has been firmly gripping the silken lines on the railings with its claws. Soon it feels the pull of the streaming threads, and when the tension is sufficient it lets go with all its claws simultaneously, vaults into the air and sails away. Sometimes a start is made prematurely and the insufficient buoyancy of the streamers causes the spider to descend almost at once, and a new start is made.
Fig. 4. Young spider preparing for an aerial voyage.
This, then, is the habitual method by which new broods of spiders distribute themselves, especially the sedentary kinds which would otherwise soon become over crowded in the neighbourhood of the parent nest. And we really need not have sought out a railing at all except for its very great convenience of observation. The same thing is going on everywhere. It largely accounts for the astonishing carpet of silk that the dew reveals to us on lawns and meadows at such times of the year. Young spiders have been busy from early dawn crawling over the grass, climbing the higher blades, and setting sail, and the whole field is covered with their lines. Railings come in handy as furnishing an elevated starting point, but any shrub or bush will do, and young spiders have been seen setting sail from the parent web itself.
McCook has given some interesting notes of his own observations on aeronautic spiders. He followed an Attid spider fifty feet till it was carried upward out of sight in a current of air. A Lycosid disappeared in the same way after being followed—at a run—for a hundred feet. The largest Epeirid he ever saw taking flight was “the size of a marrowfat pea, say one-fourth of an inch long. After having floated over a field and above a hedge-row, it crossed a road and anchored upon the top of a young tree.” But perhaps his most interesting observation was on the ability of spiders to control in some measure the duration of their flight by reefing their sails if they wish to descend, for he saw a ballooning spider collecting some of the streamers into a ball of silk which accumulated near its mouth as it gradually sank to earth.
The phenomenon known as “gossamer” has puzzled people for centuries, and English poetical literature is full of allusions to it. Chaucer classes it with “ebbe and floud” as an unsolved riddle, and Spenser, Quarles and Thomson all make mention of it, generally embodying the popular belief that it somehow had its origin in dew. “Scorchèd deaw” Spenser calls it, while Thomson’s expression is “dew evaporate.” The phenomenon in question is the occasional appearance of vast numbers of silken flakes which fill the air, and which in some recorded instances extend over many square miles and to a height of several hundred feet. Our observations will have given a clue to its origin which is entirely attributable to spiders, and in large measure to their ballooning habit, though no doubt reinforced by a large quantity of silk spun for other purposes and caught up into the air by the breeze. For a vivid account of such a shower the reader is referred to Letter LXV of White’s Natural History of Selborne, and Darwin in his Naturalist’s Voyage (Chap. VIII) records a case of the “gossamer spider” descending in multitudes on the “Beagle” when sixty miles from land.
In the ballooning habit we have the probable explanation of the wide distribution of certain species of spiders which seem at first exceedingly ill adapted for covering large distances. The Huntsman Spider, Heteropoda venatorius, is practically cosmopolitan in tropical and sub-tropical regions and the usual view has been that ships have conveyed it from port to port. McCook, however, gives several reasons for believing that the trade winds have much more to do with the matter, and this may well be the case, though both agencies have doubtless been at work.