Web structure of Latrodectus hesperus and Tegenaria agrestis . Schematic drawing illustrating (a) the tangle web of Latrodectus hesperus and (b) the sheet web of Tegenaria agrestis. L. hesperus webs consist of a dense three-dimensional tangle of threads. Glue-coated capture threads extend from the tangle to the ground. T. agrestis webs consist of a two-dimensional sheet of silk with a funnel at one end serving as a retreat. We recorded vibrations on empty webs at the active hunting location of the spider (marked by ★). The spiders indicate the position of the female’s retreat. L. hesperus web illustration modified from Blackledge et al. 2005.