The Purse-web spider spins an 'atypical' web.
The purse-web is a long silken tube with two functional parts, one above ground and the other below.
Information presented here is based on observations of Atypus karschi* in Delaware County, Pennsylvania.
The Upper Web is a tubular silk trap that can be up to 10" (25cm) long. The top is tapered to a chimney with a vent that the spider uses to exit and reenter, eject waste and prey remains, and discard dug-up soil. The chimney is the main point of upper web attachment, with silk straps and tensioning lines. The upper web is camouflaged with bits of dirt, bark and plant debris, and usually blends into its surroundings very well. Sometimes when a spider molts the shed skin (exuvia) can be found near the top of the web, having gotten stuck there when discarded.
For Atypus karschi* the upper web orientation is variable. Their webs are vertical when attached to the base of trees and shrubs, horizontal low to the ground in grassy areas and thatch, and diagonal or in discrete segments in complex vegetation. The web is held in place by a minimum of attachment threads to maintain tension and the loose tubular shape, even when the web turns a corner.
From left to right, a pair of vertical webs, a horizontal web and a 'diagonal' web stretching up into the vegetation (some grasses have been clipped away in the center and right images). All photos are from the same site at Tyler Arboretum.
The spiders spend most of their time underground in the Lower Web, rising to the upper web to catch prey and for maintenance. The lower web hangs mostly free within the burrow dug by the spider and is a compressible tube like the upper web. It ends in an expanded bulb and even underground is camouflaged with dirt stuck to the outer silk wall. The lower web breaks easily, making it difficult to find the rest of the web when excavating a spider.
The spider's burrow will curve around small obstructions like roots and stones, and living rootlets can be incorporated into the lower web silk. Sometimes tiny mounds of freshly excavated dirt are seen around the burrow entrance, and a slight funnel depression in the soil where the web enters the ground may serve to direct prey such as millipedes into the lower trap.
In winter the upper web can be destroyed by weather, soil freeze/thaw and collapsing vegetation, but the lower web remains intact. In spring it is common to see a new chimney near the ground where an old upper web is broken - and being traded in for a newer model the spider is about to build.
The Map The Spider project asks if you can find any purse-webs.
Purse-web spiders live a long time and presumably stay in the same tube for many years. The webs are visible, durable, and can be found at any time of the year. Their camouflage is quite excellent and the first time you find one it's like discovering a secret.
Can you find a purse-web in your neighborhood? at your favorite park? on your next hiking trip?
* Note: Recent DNA evidence indicates that Atypus snetsingeri is actually an introduced naturalized population of Atypus karschi from east Asia. The name 'snetsingeri' will still be used here until the official synonomy is declared in the World Spider Catalog.