JUDY JESSOP: Fall Brings the Amazing Art of Spiders Building Webs
At this time of year you can feel the whisper of change.
The night steals minutes of light from each day, yet there is still the intensity of a burning summer sun.
Spider silk is adrift, wafting with the breeze, bending sun rays to dance their shimmering length. Within the next month or so, many fall-hatching spiderlings will climb to as high a perch as they can muster. For some this precipice is the top of a blade of grass, for others the eaves of an old barn.
Once at their personal summit, they will release a long line of silk and disperse to parts unknown.
Amazingly, these minute spiderlings may drift (called ballooning) hundreds or thousands of miles. This dispersing behavior is why spiders are found worldwide, even on lonely islands and vast deserts. The only places that lack spiders are the highest snow-covered mountain peaks or permanently frozen regions of our planet.
Spider silk reaches out from wooded walks, hangs from doorways, shrouds windows, and binds stacked flowerpots. The feverish pace of web building is most evident in early morning -- neighbor's lawns are dotted with sheet webs, each bejeweled with dew diamonds winking in the early sun. Web making seems almost frantic as daylight hours shorten.
Many spiders are very large now and spinning ever-larger webs. They seem to know their time is short -- that fall is pushing forward. The spider's insect victims are now even more important as spiders mate and must expend additional energy to produce the next generation.
Amazing Spider Silk
Spider silk is a most extraordinary substance. It can be stronger than steel of the same thickness, yet so elastic that it stretches to twice its length before breaking.
The ways spiders use silk varies extensively -- there are sheet webs, orb-webs, funnel webs, tangle-webs (the common house spider) and tubular webs that run up tree trunks.
There are also net-casting spiders that carry their webs with them as they wander and trapdoor spiders that use silk to build burrows underground with a silk door they pop open to grab insects heard walking on the soil surface.
So far scientists have discovered seven different types of silk glands, each producing a different kind of silk. How many different types of silk a spider is capable of producing varies with the species. The glands are equipped with spinnerets, which can be extended or contracted and are used much like our fingers.
The spinnerets have "faucets" and "spools" and are connected to the glands by tiny tubes. Each gland produces a different type of silk in liquid form. Spiders mix and match the different types as they spin their webs.
While the spider spins, her silk hardens as it is exposed to air. Spiders often use several different kinds of silk in their web, and this, too, varies with different spiders and the strategy used to ensnare a victim.
Take an orb weaver, such as the common black and yellow garden spider, for instance. These beautiful spiders build a large circular web. Orb webs look much like a wagon wheel with spokes radiating out from the center and spirals that circle round and round from center to rim.
These spiders use a combination of very strong and elastic silk to form the "spokes" of the web, and soft sticky silk for the "spirals." It is the sticky spirals of an orb web that will ensnare the victim. Spiders that use sticky silk must be very careful to step only on the non-sticky strands of their webs or they too can become entangled.
If you have access to the Internet, this site demonstrates how an orb-weaving spider goes about the complicated process of spinning her web -- be sure to watch the videos too: http://www.conservation.unibas.ch/team/zschokke/movie.html).
Webs allow spiders to catch insects without having to use much energy to run the prey down, but web building also expends energy since spiders use a large amount of protein to produce the silk. They are able to recoup much of this protein when rebuilding, however, because they eat the old web, essentially recycling it before beginning again.
Orb weavers have poor vision so they locate prey by feeling vibration and tension on the threads of the web. The garden spider will often straddle the center of her web resting each one of her eight feet on a different spoke of the web, to feel for the vibration of a victim. Sometimes she hides off to the side under cover.
If she does, however, she is still connected to the center of the web by a non-sticky and taut signal line of silk. It transmits any vibration -- a wake-up call that her next meal has just arrived. She zips out and quickly wraps the victim, putting it out of its misery with a bite. Then the tidy bundle is hauled to a favorite spot to eat.
Most often spiders are not bright and colorful like the black and yellow garden spider. Instead, many spiders utilize strategies to look inedible or unappetizing to protect themselves from birds and other predators.
Just last summer, I encountered such a strategy, which made quite an impression on me. While working in our garden, under some pines, I sat back on my heels, and wishing for my hat, pulled off gloves and ran my fingers through tangled hair.
My rough finger comb dislodged what appeared to be a piece of bark. It looked and felt like pine bark with beautiful white lichen on one side, in a triangular shape.
My husband was also intrigued with the pattern of the lichen, and we decided to save it. I took it inside and laid it on a kitchen towel while washing my hands. As I reached for the towel, imagine my surprise to find that my pretty piece of bark had sprouted eight legs and a spider now perched in the folds.
This spider's clever defense was a trick so effective that even close examination did not give her away. If she had been perched in the center of her web, any bird in search of food would surely ignore a piece of bark caught in a spider web. I recaptured my piece of bark turned spider, placing her back where I found her in the garden.
Spiders mate in late summer.
Like many species of spiders, when a male black and yellow garden spider goes courting he does a bit of preparation first.
The sperm is produced in the abdomen but the male spider must build a special small "sperm web," put his sperm in it and then carry the package in his palps (small leg-like appendages between the mouth and first legs). Once properly equipped, he goes off in search of a mate.
Because of poor vision, the male announces his presence by plucking the strands of a female's web to signal his approach. The male is much smaller than the female and will often camp out nearby, spinning a small web at the edge of his intended's web, until she is ready to mate.
Once she accepts him, he then transfers the sperm to her abdomen where they are stored until she produces her eggs.
A week or so after mating, a female spider deposits her eggs in a silken case. Much of her energy, in these final days of summer, is expended on her descendants. Depending on the type of spider, the eggs will hatch within a few weeks and either disperse or remain in the silken nest until the following spring.
Black and yellow garden spiderlings hatch in the fall, but over-winter in egg cases, dispersing in spring. The cocoon-like case is suspended from the web for protection. Eventually, however, birds damage webs and there are a number of insects that take advantage of the garden spider's egg case for their own purposes. One study of egg cases of these garden spiders found that when spring came, in addition to garden spiderlings, there were 19 species of insects and eleven species of spiders that emerged from garden spider cases.
Whether spiders disperse in fall or over-winter in their egg cases, the art of web building must wait -- after months of winter chill the whispers of change will return -- this time daylight will push back the darkness and spring's gentle breath will awaken the landscape. It will not be long before we once again see spider webs cradling dewdrops that wink in an early morning sun.
Judy Jessop can be reached at email@example.com.
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