Rouge Valley Conservation Centre
Nature Notes
By Steve Gahbauer
September 2008
Spiders.
Spiders don't have very favourable press. Some people loathe them, some even fear them. And they are surrounded by myths and superstitions. That's sad and unfortunate, because spiders don't deserve a bad reputation. They are very useful species and play a vital role in ecosystems. They kill pests, aphids and other plant-sucking insects. They control flies, beetles and grasshoppers, but they leave alone pollinating insects, such as bees and wasps. As we shall see, they are also very interesting creatures that have a few neat tricks up their eight hairy legs.
Spiders are arachnids and there are 36,000 species world-wide, 1,500 in Ontario. The largest Ontario spider is the Dock Spider with a legspan of 13 cm. A group of spiders is called a smother. Spiders have eight legs and most species have eight eyes, but poor eyesight. They eat insects, other spiders, mites and tadpoles. The estimated mass of insects consumed annually by spiders in Canada is equal to the weight of the country's entire human population. Can you believe it?
Their predators include birds, toads, frogs, shrews, ants, wasps and centipedes. Most species live less than a year, lay anywhere from a few to thousands of eggs, and spin silk of different kinds, 1/100th the diameter of a human hair, but twice as strong as steel for its size, stretchable and elastic. Spider silk is also used by hummingbirds, vireos, flycatchers and some warblers for nest-building. All spiders are poisonous to varying degrees and all are coated with bactericides and fungicides to protect them from hungry organisms. Because of that, spiders are often used in some cultures as antibiotic dressings for wounds.
The most common spiders in our area are members of the large spider family known as orb-weavers. They construct ornate, expansive, vertical bug nets up to 75 cm wide and sit at the centre of these concentrically ringed webs in sunny but sheltered spots, waiting for their prey. They become more noticeable at this time of the year as they reach full size and build their webs higher up off the ground. Hikers will often curse their canny ability to string lines across paths just at eye level, especially early in the morning.
Most weavers rebuild their webs nightly, first gobbling up and recycling most of the old, tattered strands, which are protein, and then restringing them in as little as half an hour. With selective use and adjustment of each of their six back-end spinner valves they can vary the thickness, strength and elasticity of the silk they spin. Man-made extrusion machines don't come anywhere near this precision capability. To top it off, the centre of orb-weaver webs are threaded with spiraled rings of special sticky silk that catches flying insects.
So, how come spiders don't stick to their own webs when they walk on them? That's one of the neat tricks. A spider begins by attaching a single strand of silk horizontally between two supports. It then builds an outside rim, like a bicycle wheel, and then attaches spokes and a spiral from the centre to the outside of the web. These parts of the web are all composed of non-sticky silk. With this frame firmly in place, the spider adds the sticky strands, once again in a spiral pattern. He then connects this spiral to the non-sticky spokes. So when the spider runs across from the centre to grab a prey, it travels along the spokes, stepping on the bits that aren't sticky.
Another trick spiders have is their ability to survive cold winters. About 85% of them overwinter in soil, leaf litter and under barks. They can withstand temperatures of -20° C, even in unprotected areas, by reducing their metabolic rate. Something else may be responsible for this amazing feat, but scientists haven't figured it out yet.
The male mating instinct can even affect the quality of the web. Male orb-weaver spiders can build proper webs as juveniles, but as soon as they become adults, their attention is elsewhere. At that stage they make lousy webs, probably because they don't live very long, so they can't afford to waste time to go off and grab some dinner. Instead, they spend their time hanging around females waiting for a chance to mate – keeping, of course, to the non-sticky threads.
While all spiders are capable of of spinning silk, not all make webs. Dock Spiders, for instance, hide and run out to grab their prey instead of spinning a web to capture it. Some spiders in the Everglades even eat fish.
Most Ontario spiders mate in early summer and then wrap their eggs in yellowish cocoons. Dock Spiders tote their egg sacks around with them. Wolf Spiders even carry their hatchlings on their backs for up to 10 days.
Soon after hatching, the tiny spiderlings swarm to the tops of plants or shrubs and spin a thin strand of silk, which catches in the slightest breeze and lifts them up into the air. This is called “ballooning” and in Ontario it occurs in the autumn. This manoeuvre distributes them over wide distances and keeps the spider population from becoming too concentrated in one area. As night falls, the silk becomes moisture-laden and the tiny para-troopers drop back to the earth.
On your walks through the Rouge Park this fall, watch for those marvelous spider webs with dew drops attached to them, glistening in the morning sun, and instead of becoming annoyed at silk strands across the path, think about what smart, interesting and useful creatures spiders really are. Happy hiking!
Sources: Cameron Smith, Doug Bennet, Tim Tiner, University of Toronto, Bird Studies Canada.
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