A bridge orb weaver (Larinioides sclopetarius) suns at the Unity park in November. Photo by Dana Wilde

A late September chill this year seemed to bring autumn back in line with its natural past, and the spiders that hang out on the storage garage at the Unity park disappeared into their cold-weather haunts.

Shreds and patches of old silk and insect body parts dangled and flapped in the eaves and nooks of the logs. Then, in mid-October, it got ridiculously warm again, as it has in every recent October, and some of the spiders returned to work, lingering right into November.

These are bridge spiders, scientifically known as Larinioides sclopetarius. They’re also called gray cross spiders because the leaflike marking on their backs resembles an ornate cross, when you look at it just right, similar to the cross on the back of the cross spider (Araneus diadematus), a fairly common garden spider hereabouts.

Bridge spiders and cross spiders are both orb weavers, meaning they spin those familiar spiral-shaped webs to capture their meals. While the cross spider’s web is seen in vegetation as often as buildings, bridge spiders get their name from their presence mainly on bridges or other structures overhanging water, where small gnats, a preferred food, mainly live.

The storage garage at the park is 40 or 50 yards from the Unity Pond shore, but close enough for there to be enough small aquatic-associated flying bugs to encourage scores of bridge spiders to set up webs in the eaves and nooks of the log building. The latter part of every summer, it’s a miniature setting for a Stephen King story. “Sclopetarians,” as I refer to them for my own science-fictional purposes, of all ages and sizes industriously spin and repair orb webs so crowded together they often connect to each other.

Most spiders are solitary and do not form groups, mainly because they’re apt to eat each other. But bridge spiders tend to live in these big “parasocial” colonies (known in my private lexicon as the sclopetariat), in which they cooperate to the extent that they leave each other alone while they work in close proximity. This kind of loose cooperation is in contrast to a few species of “social” spiders who actually join forces in foraging, sharing prey, taking care of webs, and in some cases even caring for babies. No full-on socialist spiders are known to live in Maine.

Two other species of Larinioides do live here and look a lot like L. sclopetarius — they are L. cornutus (furrow spider) and L. patagiatus (foliate or ornamental orb weaver). Both are less conspicuous than the sclopetarians. It’s hard to tell for sure, but L. patagiatus seems to live underneath a bench along the park walking track.

When I first noticed the spiders on the storage garage, I was unsure exactly who they were. Larinioides sclopetarius is probably not native to North America, and some guides and studies say it’s uncommon here. Most of the available studies on them were done in Europe, and practically every authority describes them as nocturnal. Many orb-weaving spiders build their webs in the evening, catch bugs all night, then take down 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 bright sunlight all day.

Natural historian Kenneth Frank noticed the same daytime behavior of the spiders on a bridge in Philadelphia. Puzzled about it, like me, he turned up similar observations at the same bridge by Henry C. McCook, an influential amateur arachnologist in the 19th century. McCook suggested bridge spiders are actually diurnal, synchronizing their activity to the prey’s activity. When the prey are near the bridge, the spiders set about to catch them, day or night. Frank also found studies documenting bridge spiders’ attraction to artificial light, no doubt because gnats fly near lights.

Well, city bridges have lights, and as it happens, so does the storage garage, with floodlights along the eaves that no doubt attract gnats and other flying bugs by the thousands. You can tell by the welter of webs there that no small flying or crawling thing is safe from the sclopetariat.

In early November, I noticed, on the end of a log overhang, a brand new little orb web maybe 4 inches across, glistening in the low-angled autumn sunlight. The web itself was practically perfect in symmetry and spacing, suggesting its owner was young. In some orb-weaving species, young spiders build the tidiest, most perfectly formed spirals. Older spiders learn to adapt their webs to conditions, and often spin less perfect-looking, but probably more effective, snares. Sure enough, the small young owner was sitting right in the middle of its new and perfect web, waiting for a bug to hit.

Bridge spiders are thought to live a year or two, and in Europe, at least, all ages of them are active through the winter. I’m not sure if that’s true here in Maine’s cold. I think they may overwinter in cracks and crannies, maybe in a hibernation-like state that allows them to perk up when they sense enough warmth. This is just a conjecture.

But it might explain why the sclopetarians disappeared in the September chill, then returned to their horror show in creepy warm October and November.

Dana Wilde lives in Troy. You can contact him at dwilde.naturalist@gmail.com. His book “A Backyard Book of Spiders in Maine” is available from North Country Press. Backyard Naturalist appears the second and fourth Thursdays each month.