Sunday, January 17, 2016

Triangle spider wields web as a sneaky snare

A tiny triangle spider holds its web


January 17, 2016

Jim McCormac

I hate to break it to you, arachnophobes, but spiders are everywhere, even when snow flies and the air is super-chilled. The ones in your house (and there are many) have it easy. Not so with the spiders that remain feral and outdoors, where most people wish they would stay.

Huge numbers of spiders spend winter in leaf litter, in tree bark, and on twigs and branches. On wintry days when the temperatures rise above freezing, some become active and go on the hunt.

Dec. 12 was relatively balmy, with afternoon temperatures reaching almost 50 degrees. I met naturalists David and Laura Hughes at Clear Creek Metro Park on the north edge of the Hocking Hills for photography and exploration. Clear Creek is a biological hot spot and always produces interesting sightings.

We hadn’t gone far down a trail when Laura spotted a tiny web, over which an even tinier spider stood vigil. She had found the amazing triangle spider (Hyptiotes cavatus).

The triangle spider constructs a perfect vertical wedge of a web; sort of a silken pie slice of doom. This web is far easier to spot than the 3-millimeter spider that tends the trap.

As the spider completes the web’s construction, it ratchets the small end taut via an anchor line. It pulls this line ever tighter, until the spider is holding the web under great tension, like an archer who has drawn a bowstring to full tautness.

When prey — usually a tiny insect — hits the web, the spider releases the anchor line. The web goes slack and engulfs the victim in a sheet of silk. Sometimes the spider gives the web a few hard jerks to further ensure that the prey is entangled.

The triangle spider belongs to the Uloboridae family, which is mostly tropical — only 16 species occur north of Mexico. While most spiders produce sticky silk, these spiders create nonsticky silk via a specialized organ called the cribellum. Such silk is soft and puffy, and when employed as a quick-release snare is quite effective at snagging victims.

Another noteworthy oddity of Uloboridean spiders is that they are nonvenomous. All other North American spiders possess potent venom. When a victim is snared, the triangle spider rushes out and deftly enshrouds it with dense wrappings of silk, like a mummy embalmed by an overzealous undertaker.

When the wrapping is complete, the spider bites the thoroughly immobilized prey through the silk. The bite releases potent digestive enzymes, which serve to rapidly liquefy the victim’s innards. As noted by Dr. Richard Bradley, author of Common Spiders of North America, “The extensive wrappings of silk may assist in holding the gushy mass together during feeding.”

After consuming its meal, the little spider fastidiously reorganizes its web, tightens the drawstring and awaits another victim.

Naturalist Jim McCormac writes a column for The Dispatch on the first, third and fifth Sundays of the month. He also writes about nature at www.jim

No comments: