Backyard Naturalist: The Tangled Webs of Bridge Spiders

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A bridge orbweaver (Larinioides sclopetarius) sunbathes in Unity Park in November. Photo by Dana Wilde

This year, a late September chill seemed to reconcile fall with its natural past, and the spiders loitering around Unity Park’s storage garage disappeared into their favorite cold-weather haunts.

Scraps and stains of old silk and body parts of insects dangled and fluttered in the eaves and corners of the logs. Then, in mid-October, it got ridiculously warm again, like every last Octoberand some of the spiders returned to work and stayed well into November.

These are bridge spiders, scientifically known as Larinioides sclopetarius. They’re also called gray garden spiders because, if you look closely, the leaf-like marking on their back resembles an ornate cross, similar to the cross on the back of the garden spider (Araneus diadematus), a fairly common garden spider here.

Bridge spiders and cross spiders are both orbweavers, meaning they spin those familiar spiraling webs to catch their meals. While the cross spider web can be seen in vegetation as often as buildings, bridge spiders get their name from their presence primarily on bridges or other structures hanging over water, where small midges live mostly, a preferred food.

The storage garage at the park is 40 or 50 yards from the shore of Unity Pond, but close enough to have enough small aquatic flying bugs to trick dozens of bridge spiders into webs in the eaves and corners of the log home. In the second half of each summer, it’s a miniature setting for a Stephen King story. “Sklopetarians,” as I call them for my own sci-fi purposes, diligently spin and repair webs of spheres of all ages and sizes, crowded so closely together that they often bind together.

Most spiders are solitary and do not form groups, mainly because they tend to eat each other. But bridge spiders tend to live in these large “parasocial” colonies (known as slopetariat in my private lexicon) where they cooperate to the extent that they leave each other alone while working in close proximity. This type of loose cooperation contrasts with some species of “social” spiders, which actually band together in foraging, sharing prey, tending webs, and in some cases even tending babies. No truly socialist spiders are known to live in Maine.

Two other species of Larinioides live here and look very similar to L. sclopetarius – they are L. cornutus (furrow spider) and L. patagiatus (leaf or ornamental orbweaver). Both are less conspicuous than the slopetarians. It’s hard to say, but L. patagiatus seems to live under a bench on the park’s walkway.

When I first noticed the spiders on the storage garage I wasn’t sure who they were. Larinioides sclopetarius is probably not native to North America, and some guides and studies say it’s uncommon here. Most available studies on them have been conducted in Europe, and virtually every authority describes them as nocturnal. Many orbweaving spiders build their webs in the evening, catch bugs all night, then detach the web in the morning by eating it and recycling the silk proteins in their system for the next night’s web.

But the Unity Bridge spiders are conspicuously busy spinning and repairing in the bright sunlight all day.

Natural historian Kenneth Frank noted this the same daytime behavior of spiders on a bridge in Philadelphia. Puzzled, as I was, he came across similar observations at the same bridge by Henry C. McCook, an influential nineteenth-century amateur arachnologist. McCook suggested that the bridge spiders are in fact diurnal and synchronize their activity with that of prey. When the prey is near the bridge, the spiders set about catching it, day or night. Frank also found studies documenting bridge spiders’ attraction to artificial lights, no doubt because mosquitoes fly near lights.

Well, city bridges have lights, and coincidentally, the storage garage does too, with floodlights along the eaves, no doubt attracting mosquitoes and other flying bugs by the thousands. You can tell by the tangle of webs that no small thing, flying or crawling, is safe from the slopetariat.

In early November, I noticed a brand-new little spider web, maybe 4 inches across, at the end of a log overhang, glistening in the flat autumn sunlight. The web itself was virtually perfect in symmetry and spacing, suggesting that its owner was young. In some orb-weaving species, young spiders build the neatest, most perfectly formed spirals; older spiders learn to adapt their webs to the conditions, often spinning less-than-perfect-looking but likely more effective traps. In fact, the little young owner sat in the middle of his new and perfect web, waiting for a bug to strike.

Bridge spiders are thought to live to be one or two years old, and in Europe at least, they are active throughout the winter at all ages. I’m not sure if this is correct in Maine’s cold; I think they hibernate in nooks and crannies, perhaps in a hibernation-like state that allows them to perk up if they feel enough warmth. This is just a guess.

But it might explain why the Slopetarians disappeared into the cold of September and then returned to their horror show in the creepily warm October and November.

Dana Wilde lives in Troy. You can reach him at [email protected] His book “A Backyard Book of Maine Spiders” is available from North Country Press. Backyard Naturalist is published every second and fourth Thursday of the month.


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