Some people duck and walk sideways to squeeze past them. Others flail their arms to slap them away. But almost everybody who lives in the leafy parts of Eugene steps outside on summer mornings to see them glistening in the sun: freshly spun spider webs.
What kind of spiders spin these webs? Why are there so many of them this time of year? And why do they keep building webs where we walk, no matter how many times we knock them down?
Itís easy to tell which spider family they belong to from the web they weave. Not all spiders spin webs, and many make sloppy diffuse webs. The Eugene spiders that spin the classic spiral web are members of the Araneidae family, commonly known as orb weavers.
All orb weavers have three claws, eight eyes and eight legs. According to the website bugguide.net, identifying the exact species of an individual spider requires special equipment and uncommon expertise: "For most orb weavers, the ability to classify a specimen to species level often requires a microscopic inspection of the genitalia. "
But anybody can identify a female orb weaver. Females are the only ones to build orb webs, and they do so for female reasons: every summer they lay an egg sac. During winter, spiders are inactive, close to the ground and out of sight. Spring heats up their metabolism, which makes the females hungry because laying eggs requires lots of nutrients. Come summer, females build webs higher off the ground to fatten on flying insects.
The reason we see so many webs this time of year is because flying insect airspace is roughly human face level.
These spider girls repeatedly build in places where we walk because their sense of time is pretty rudimentary. At 4 a.m., several hours have passed since anybody has walked down your front steps. So a spider concludes that your front steps must be the ideal secluded spot to catch insects.
She weaves in the dark, by feel. First, she establishes a bridge line, the horizontal strand that holds up the web. She does this by spinning out a line that floats away in midair until she feels it stick to an anchor point in the distance. She then pulls the line taught and runs back and forth to reinforce it with multiple stands.
Under the bridge line, she constructs the webís frame out of foundation lines anchored to two or three other points. She then fills in the frame with lines that radiate from the center like spokes on a bicycle wheel. Finally, she circles outwards from the center to lay down the "capture spiral. " She returns to the bullseye at the center of the capture spiral and waits upside down, pulling lines with her claws to detect the vibrations of a struggling insect.
Fast-flying insects with good eyesight are hard to catch. But an orb web is equipped with special features that encourage bugs to blunder into the snare. Sunlight reflecting off the web causes the strands to glimmer. These shiny strands attract flying insects to buzz in for a closer look.
By contrast, parts of the web in shade are invisible, which a zooming insect perceives as an escape route. When the bug cuts to escape, it crashes into the capture spiral.
To withstand the crash force, the web has to be strong enough not to break, but soft enough not to bounce the insect away like a kid rebounding off a trampoline.
Orb webs can do this because they are constructed out of two distinct types of line, a combination that gives orb webs that mysterious quality of appearing both sturdy and flimsy at the same time. The bridge line, frame lines and spokes are made of strong dry silk. But the capture spiral is made of flexible, elastic silk which is coated with beads of sticky glue.
You might notice this difference the next time you walk into a web. The strong dry silk pulls against your skin, then snaps. The stretchy sticky silk tangles in your hair and clings to your forehead.
At this point, most nature articles would extol the spiderís contribution to our ecosystem, as if that could make people accept the creepy experience of catching a web in the face. But Melissa Scherr, executive director of the Northwest Entomological Research Center, says nothing will make people more patient with webs.
Walking unexpectedly into a spider web triggers a temporary but primordial arm-flailing panic that Scherr believes no one is immune to.
Despite her Ph.D. in entomology, she admits: "Even I get the heebie jeebies when it happens to me. "