In parks and gardens around most North American cities, fall means spider webs. Lots of them. They festoon rosebushes and porch swings. They collect dew and attract photographers.
Not Just in Fall
At no time of year are spiders more conspicuous than early fall. But that doesn’t mean there’s some kind of population explosion. The orb-weaving spiders that produce these webs have been around since they emerged from their egg sacs in spring. In Europe, Asia, southern Canada, and the northeast and northwest United States, it's often Araneus diadematus, the European garden spider.
“They’re pretty much there all growing season long,” says Todd Murray, an educator in horticulture and agriculture with Washington State University Cooperative Extension.
In fact, orb weaving spider’s fall numbers are a tiny fraction of the spring population.
But in spring, the spiders are harder to spot.
Spring
They stay in the pouch-like egg sac with about 500 of their brothers and sisters until the temperature is warm enough, says Rod Crawford, Curator of Arachnids at the Burke Museum of Natural History and Culture in Seattle. When they crawl out they look like a pile of grain with many tiny legs.
Sometimes, the little spiders will shoot a line of silk into the air to catch the wind, then drift where the wind goes.
Summer
The ones that survive over the summer will swell as they eat insects. How big they become depends on their food and water supply, Crawford says.
The weather is also a factor. Because they are cold-blooded creatures, spiders depend on good temperatures to be able to metabolize food and grow, Murray says.
Predators eat most of the spiders. Of the hundreds of females that scrambled out of the pouch in the spring, on average one will survive to make an egg sac of her own, Crawford says.
Fall
Mating marks the end of the spiders’ lives. Once males start mating they stop building webs, Crawford says. They use all their energy going from web to web, wooing females, getting by on whatever insects they find on the way. They don't last long.
The females spin their egg sac and lay their eggs, and stay, guarding the egg sac until they die days or weeks later, Crawford says.
Feeding
The look of a spider’s web depends on a spider’s species. The orb weaver’s wheel-shaped web is covered in sticky thread, placed to catch flying insects. When a large enough insect gets stuck in the web, the spider bites it and wraps it up. Once the insect is dead, the spider can begin the messy business of eating it.
We digest our food inside our bodies. Spiders do it out on the web. They vomit their digestive enzymes onto the insect. When the spider chews up all those enzymes can yield, it'll vomit more until it can chew up all the insect but its hardest parts.
The spider leaves the smallest insects alone until it is time to eat up the web, Crawford says. Then the little bugs amount for extra nutrition when the spider stuffs the silk in its mouth.
Web Walking
Orb weaving spiders don’t get caught in their own webs because they have special claws on the ends of their feet. The notion that they have oil on their feet to keep them from getting entangled is one of several myths about spiders, Crawford says.
