Sonoma County’s spider population in high gear for October

With Halloween coming up, black plastic spiders enmeshed in synthetic webbing have crept into neighborhoods and grocery stores.

Yet the explosion of spiders this time of year is about much more than their association with the spooky holiday tradition. Fall is the main event for most spiders. This is the time when we see spider webs in nature sparkling with dew and laden with egg sacs. We see glimmers of gossamer silk on the breeze, carrying young spiders to new homes. We find congregations of cellar spiders in the corners of our showers, kitchens and living rooms. And, as those of us who weep at the end E. B. White’s classic Charlotte’s Web know all too well, fall is the end of life for many beloved spiders.

It is tempting to divide humans into two camps: those who hate spiders (squishers) and those who admire them (carrying them outside in a jar or paper towel). There also is a growing contingent of humans, personified my colleague and winner of Wildcare’s 2017 Terwilliger Environmental Award Gwen Heistand, who absolutely loves all things creepy and crawly. Gwen will adjust her own lifestyle to accommodate the spiders that show up on her window sills and doorways.

“I don’t open that door at all any more,” she explains, pointing to a door in her kitchen ensnared in a complex of spider webs and their egg sacs. What I have found, and what Gwen has taught me, is that with even just a little bit knowledge, most of us can become spider lovers.

Spiders are literally everywhere: on beaches, under rocks, in the soil, ballooning in the upper atmosphere, in the canopy of trees, and of course in our homes, especially, it seems, in our showers. While all spiders make silk, and all spiders are carnivores, not all spiders weave webs. The classic circular spider web is made by a group of spiders called orb weavers. Another group, called sheet web weavers build dense filmy structures sometimes shaped like funnels, domes, or even cups and saucers to trap their prey. Our common wolf spiders, on the other hand, chase down their prey on foot, using silk primarily to construct their protective egg sacks and attract a mate. Burrowing spiders like false tarantulas and turret spiders line their tunnels and towers in silk, with the dual purpose of providing stability and alerting the spider when prey or danger is near.

Depending on the species, a single spider can make up to seven different kinds of silk, each with its own purpose. Spider silk starts as a liquid protein produced by special glands and then extruded through tiny spigots in the spinnerets located on the underside of the spider’s abdomen. Dragline, or ampulate, silk is the strongest; only a few microns in diameter, it is stronger per unit weight than steel. Used as a tether, dragline silk allows spiders to rappel out of danger or just to get from one place to another. Orb weavers use this type of silk to frame their webs and then another stretchy spiral-capture silk to weave the net that snares unwary insects. Tough swathing silk is used to wrap struggling prey while a softer cocoon silk forms the cozy and protective egg sac.

Indeed, each of these of the unique materials are spectacular feats of engineering that humans are only now coming to understand. “Spiders have so much to teach us,” insists Heistand, who points out that for years, scientists have been trying to unravel the mysteries of spider silk to adapt to human uses. For example, orb weavers use silk that reflects ultraviolet light, in part to prevent birds from crashing into and destroying the web. Inspired by this idea, a company has recently incorporated an invisible (to humans) “web” of U.V. reflective film into glass. Just as spider silk warns birds away from webs, this new “bird-friendly” glass warns them away from windows. The hope is to reduce the hundreds of millions of birds killed by collisions with window glass every year. The properties of spider silk also are being studied for a range of mind-blowing applications in construction and medicine. Imagine flexible bridge suspension cables, super-strong bungee cords, or even delicate scaffolding for organ replacements.

Which spiders are here now?

Although they’ve actually been around since spring, large yellow and black garden spiders and silver-banded garden spiders seem to appear out of nowhere in fall. Fall is when the females become reproductively active, growing larger and constructing egg sacs. Classic orb weavers, our local garden spiders can be seen hanging head down in the middle of their large webs on top of a zig-zag of silk called a stabillimentum. Although once thought to provide stability to the web (hence the name), the stabillimentum may actually provide camouflage or reflect ultraviolet light, warning birds away.

Pumpkin spider

Also an orb weaver, the charismatic pumpkin spider is much more elusive than the garden spider. This rotund beauty builds a “retreat” at the edge of her web where she hides, keeping one leg on a signal line of silk leading to the center of the orb. The signal line alerts the pumpkin spider when prey or danger are near. To find the spider herself, follow the signal line from the center of the web to the retreat, which may look like a clump of leaves or grass.

Black widows

The black widow spider is one of only two spiders in California capable of harming humans (the other is the brown recluse). With the red hourglass tattoo on her tummy, the black widow is probably the most recognizable spider to most North Bay residents.

Black widows can be found both indoors and out in a messy tangle of web classically called a “cobweb.” Black widows are definitely venomous, but they are not aggressive; most bites delivered to humans are defensive. The neurotoxic venom of the black widow can cause mild to severe symptoms ranging from intense pain to muscle cramps and convulsions.

Fortunately, current anti-venom drugs are highly effective and death from a black widow bite is extremely rare. If you are bitten, seek medical attention immediately.

Silvery false tarantula

One of my favorite spiders is the beautiful silvery false tarantula. Alert hikers are much more likely to spot the false tarantula’s burrow than the nocturnal spider herself. Look for an almost perfectly round hole on a trail, about the size of a dime or nickel, rimmed with a collar of spider silk. In the fall, often after the first rains, false tarantulas will clean out their burrows, leaving a scattering of detritus around the burrow opening. If you are lucky, you may find a whole spider exoskeleton (last year’s molt) or a white spongy sphere (last year’s egg sack). Baby false tarantulas actually stay in the egg sac through their first molt. As a result, if you peek into last year’s egg sack you’ll likely see hundreds of tiny brownish exoskeletons.

Wolf spider

The wolf spider is one of those spiders that eschew the web in favor of hunting down their prey.

“These are the cheetahs of the spider world,” says Heistand, who notes one often sees wolf spiders running through the grass in moist areas and near ponds and streams. As hunters, wolf spiders see very well thanks to relatively huge eyes arrayed at multiple angles. Female wolf spiders are very good mothers, carrying their egg sac attached to their spinnerets until the eggs hatch. After that, the spiderlings climb onto her back for a protective maternal ride lasting 7 to 8 days.

Turret spider

No spider hunt is complete without finding the home of at least one turret spider. An architect extraordinaire, the turret spider uses its silk and other materials to construct a tower at the top of its burrow. The tower is reinforced with whatever natural materials the spider can find, especially fir needles, leaf litter, moss, and lichen. The turrets range in size; the largest are often several inches tall.

Once you find one turret, you are likely to discover more, arranged in a village-like grouping with the small towers of younger spiders surrounding the parental home. Like the false tarantula, the turret spider is nocturnal.

Curious hikers armed with red lights can see the spiders sitting at the tops of their turrets, waiting for prey to happen by.

Jeanne Wirka is the Director of Stewardship for Audubon Canyon Ranch. She lives in Sonoma.