Orb Weavers

Argiope aurantia, a large spider with black and yellow markings, is a common visitor to many gardens.  I watched one in our garden weave a new web.  The spider started by attaching a strand of silk to an anchor point about halfway up a sunflower stalk.  Then the spider dropped downward, releasing a strand of silk behind it until reaching a new level.  It attached the strand to a single point and doubled the strand back to the beginning point.  It repeated this process to several new points around the first anchor, eventually creating a pattern that looks like the spokes of a wheel.  Each strand is stretchy, and as soon as it leaves a strand, its weight having stretched it downwards, the strand snaps back to a taut line between its two end points.  The spider then starts to make a spiral from the center point working outward.

Spiders are classified by the type and shape of the web they weave.  Funnel weavers make a cone of dense silk walls that taper downward directing the prey to the bottom where the spider waits.  Others spin a variety of silk strands with no discernible pattern.  Orb-weavers, like the one described above,  construct a large circle with spokes radiating out from the center.  Hunting spiders do not weave webs at all, preferring to stalk and chase their prey. 

All spiders produce silk for use in reproduction, web-building, comfort, and moving around their habitat.   Spiders can produce two kinds of silk strands, ones that are dry and ones that are tacky.  After laying their eggs, females will use tacky silk to wrapped each egg into a silk sac for protection and warmth.  Burrowing spiders use strands to line the inside walls of underground dens.  Dry strands become draglines used to climb on or hang from when moving from one perch to another. 

The spokes of an orb-weavers web are made from dry silk strands.  The spiral wound from the center across all the spokes in several circles, each larger than the previous one, are made from tacky strands.  Insects encountering the web by crawling or flying into it get caught by the tacky strands and are trapped.  A single dry strand called a trip line runs from the center of the web to the spider sitting quietly underneath the web.  When the struggling insect vibrates the web, the trip line signals to the spider to come out, biting the insect to inject venom, and wrapping its prey in more silk.  The prey is left hanging in the web for a later meal.

Orb weavers and their webs are easy to find.  They eat many insects in our gardens and are a natural form of pest control.  They make great subjects to observe to learn many of their behaviors including building webs, catching prey and feeding.  In summertime, you may also observe courtship, mating, and egg-laying activities.  Watch for these easy to find and fascinating garden companions!