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retreat either retains its primitive simplicity in association with a new structure, the snare or net, or is entirely superseded by the latter.
Perhaps the most rudimentary form of snare arose from the spinning of threads round the mouth of the tube to hold it in place.
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.
Snares of another type consisting of a tangled mass of threads amongst which the spiders pick their way with ease, but which are impassable to insects, are spun by members of the Theridiidae and Pholcidae; but by common consent the so-called orbicular web, so characteristic of the Argyopidae but by no means confined to them, is regarded as manifesting the greatest perfection of instinct in snare-spinning.
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.
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.
Spiders which spin no snare are dependent for capturing prey for the most part upon their quickness or powers of lying concealed.
The tarantula, like all its allies, spins no web as a snare but catches its prey by activity and speed of foot.