Passing back from the centre of the web to the underside of an adjoining leaf or some other sheltered spot runs a single thread, the trap line affording passage to the spider to and from the sheltered spot and the snare itself.
Be that as it may, the snare in many instances, as in that of the Agalenidae (Tegenaria, Agalena), a family closely allied to the Lycosidae, is a horizontal sheet of webbing, upon which the spider runs, continuous with the lower half of the aperture of the tube, of which it is simply an extension.
Again some species of Dictyna, belonging to the Amaurobiidae, also have a tubular retreat opening on to the surface of a snare in which a crude attempt at a radial and concentric arrangement of the threads is perceptible.
In constructing, therefore, a snare of radiating and concentric lines, it seems that a spider economizes both time and silk and in addition renders the web as strong and as serviceable and yet as delicate and invisible as possible.
But he was also conscious that his exquisite devotion to mere lucidity and beauty might be a snare to him, and a happy instinct was always tlriving him to a study of mankind as well as of inanimate nature.
To the web is attached a trap-line which when drawn taut holds the snare stretched and tight, and when relaxed loosens the whole structure so that the threads fall together.
But those wild eyes met his, as the bloodshot eyes of the prairie wolves meet the eye of their leader, ere he rushes on at their head in the trail of the bison; but, alas! only to fall into the hidden snare of the Indian.
Spiders which spin no snare are dependent for capturing prey for the most part upon their quickness or powers of lying concealed.
Along one line there was a gradual elaboration of the tube until it culminated, so far as structural complexity is concerned, in the so-called trapdoor nests or burrows of various families; along the other line the tubular retreat either retains its primitive simplicity in association with a new structure, the snare or net, or is entirely superseded by the latter.
The tarantula, like all its allies, spins no web as a snare but catches its prey by activity and speed of foot.