Spiders produce different types of silk for different purposes, including draglines, egg sacs, ballooning, building a web and wrapping prey. Much of the silk spiders use to spin webs has a sticky consistency, in order to catch flying insects. It turns out that sticky silk isn’t the only reason spider webs are such efficient insect catchers.
According to scientists at Oxford University, not only is much of a spider’s web silk sticky, but it is coated with a glue that is electrically conductive. This glue causes spider webs to reach out and grab all charged particles that fly into it, from pollen to grasshoppers. Physics accounts for the web moving toward all airborne objects, whether they are positively or negatively charged.
According to Prof. Vollrath of Oxford University, electrical attraction also drags airborne pollutants (aerosols, pesticides, etc.) to the web. For this reason, it’s been suggested that webs could be a valuable resource for environmental monitoring. (Thanks to Elizabeth Walker and Linda Fuerst for introducing me to this phenomenon.)
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If there is a fairly large spider spinning orb webs in a corner of your shed or barn and it has striped gray, brown and white legs, chances are great that it is a Barn Spider, Araneus cavaticus. These spiders are nocturnal, so it’s often the early-rising/late-to-bed folks that observe these arachnids. During the day, Barn Spiders hide in a nearby crevice where birds and other predators cannot easily find them. Webs are freshly constructed every night (or every few nights) and the remains of the old web are eaten in order to conserve the valuable silk. During the night Barn Spiders can be found hanging in the center of their web, awaiting prey.
Male Barn Spiders reach between ¼” and ½” in size and adult females typically are around ¾”. Most males spin webs less frequently and spend much of their lives wandering, attempting to find a female to mate with. Thus, most Barns Spiders you see in webs tend to be females.
The spider in E. B. White’s Charlotte’s Web was based on a Barn Spider. In his inimitable way, White named her Charlotte A. Cavatica, a reference to the Barn Spider’s scientific name. One of Charlotte’s daughters, after asking what her mother’s middle initial was, names herself Aranea.
Naturally Curious is supported by donations. If you choose to contribute, you may go to http://www.naturallycuriouswithmaryholland.wordpress.com and click on the yellow “donate” button.