Sheetweb Spider - Drapetisca alteranda [1]
Family Linyphiinae - 2nd largest family of spiders after Salticidae
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Live adult sheetweb spiders photographed at northern Illinois

Sheetweb Spider - Drapetisca alteranda

Linyphiidae is the second largest family of spiders after Salticidae.  Comprised of 4,300 described species in 578 genera, this family is poorly known because of their small size.  Commonly called sheetweb spiders (subfamily Linyphiinae) and dwarf spiders (subfamily Erigoninae).

Sheetweb spiderwebs can be flat, convex or concave, or can simply hug the substrate contours, as this spider demonstrates. She has constructed her web on a fallen log, drenched in condensation on the forest floor - an environment not particularly conducive to the rapid movement she needs to capture prey. So instead of mucking about in the moss and lichens and liquid, this spider is supported on silken strands she grips with claws at the tips of her legs. This gives her the advantage of speed, and also imparts a network whereby prey movements are communicated almost instantly to her vibration-sensing equipment. I see orb-weavers remain hidden while surreptitiously holding a thread integrated into the orb; it works just like a child's tin-cans-and-string telephone. (Tin-can telephones really do work, in case you've never tried it, soup manufacturers' TV ads notwithstanding; the key being the string must be stretched taut in a straight line between the cans, thereby very effectively transmitting the sound of a human voice through the serial connection of fiber.)

Other types of spiders do construct sheet-like webs to facilitate personal transport; the funnel-weaver spiders, with their characteristic conspicuous sheet-and-funnel, some jumping spiders use parts of their shelter web to move into and out of their hunting grounds; some orb-weavers use web scaffolding to move among and between plants over great distances. Even some wolf spiders, often thought of as free-ranging hunters, use web scaffolding to extend their range.  These webs are usually nearly invisible and escape our notice - it is only via photography that I have become aware of the vast number of common spiders that use their silk in this manner.

Sheetweb Spider
Spider's freshly spun silk
Sheetweb Spider
Exquisitely camouflaged, this spider is suspended on her sheet web. Perspective may be gained by observing the water droplet above her.
References
1. Bugguide.net, Drapetisca alteranda
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Class Arachnida / Order Araneae: Spiders are the largest group of arachnids.  They are easily recognized by their eight legs. The vast majority of spiders are completely harmless and offer beneficial services, chief of which is keeping the burgeoning insect population in check. All spiders are predacious and carnivorous. They subsist on the bodily fluids and chewed up live insects they have paralyzed with their venom.
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