Web-based hunters
The simple suspended sheet web of a primitive Tasmanian spider (Hickmania troglodytes). This web may resemble those made by the original cribellate spiders. Photo: © R Morrison.
The sheet web of the Black House Spider (Badumna insignis). Photo: M Gray © Australian Museum.
Orb web. Photo: © J Frazier.
The ancestors of today's araneomorph spiders used cribellate (wool-like) catching silk, probably in some form of a simple sheet web, to capture their prey. These webs are still common today. They are made by primitive cribellate spiders like the Tasmanian Cave Spider, Hickmania troglodytes and many modern spiders like the striped sheet web spiders (Therlinya spp). make such webs. The common Black House (Window) Spiders progressively thicken their sheet webs with several silk layers - the shawl-like webs. Most of these webs are built out from a crevice retreat in a soil bank or tree trunk. By contrast, Hammock web spiders sit on the rock or wood substrate shielded by their hammock-like sheet web. These webs are effective for capturing walking and jumping prey but will also entangle flying prey like moths and flies.
Insects provide the vast majority of spiders' food and many web-based prey catching strategies evolved in response to this plentitude. These included 'space webs', 3-D webs with a maze of threads that delay the prey long enough for the spider to enswathe it in silk or bite it; knockdown webs combining a maze of lines above with a silk sheet below - the maze of 'knockdown' threads stop flying or jumping prey which fall onto the sheet below and also help keep the sheet clear of debris; orb webs, with large, planar catching surfaces that are sticky, strong and stretchy and virtually invisible to flying insects; sticky 'gum-footed' webs like that of the Redback Spider that catch walking prey; and many others. Many of these web builders use silk enswathing and wrapping to subdue and 'package' their meal for immediate or later consumption
Despite its great success as an insect trap, the orb web has undergone some interesting specialisations. For example, moths are a very abundant food source. The body and wings of moths are covered in scale-like hairs that can be easily shed, and this often allows them to struggle free of a silk trap. However, some orb web weavers have evolved long, ladder-like orb webs. In such elongate webs, moths lose so many scale hairs while struggling to get free that they become stuck before they can roll out of the web.
Even more specialised prey capture strategies have evolved in other descendants of orb weaver lineages. These involve simplification and modification of the orb web and highly specialised web handling behaviour. Two notable examples are the Bolas Spiders (Ordgarius), another moth specialist, and Net -casting Spiders (Deinopis).
Find out more
- Types of spider webs
http://www.amonline.net.au/spiders/life/prey/web_types.htm
