Your face is not what Micrathena gracilis wants to eat. It prefers flies. But hikers, mountain bikers, and trail runners in St. Louis know what awaits them in August and September: an endless series of sticky webs strewn across local trails, at face level, prompting sour tffffft expressions and the inquiry: Is there a spider on me right now?
Don’t fret, says David Bruns, educator at the Missouri Department of Conservation. This spiny orbweaver, which authors a great many of these webs, is “harmless to humans.”
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True, Bruns points out, it’s not the only spider on local trails; there’s also the arrowhead orbweaver (Verrucosa arenata), which has a white triangle on its abdomen. But M. gracilis is the most common. And you might even show it some mercy, given that it eats things humans find annoying (flies and mosquitoes).
Here are four things to know about M. gracilis.
1. They eat their own webs every day
The males are reclusive; females are the ones you see. They’re the web spinners.
After establishing a reusable outer frame connected to trees or bushes, they erect a new adhesive spiral each morning. By day, they hang out near the middle and wait for their prey. At dusk, they eat that spiral, then retreat to a hard surface for the night.
2. Why webs proliferate around St. Louis in August and September
M. gracilis only lives for a year, so by mid-summer, they’ve reached maturity and are building their biggest webs. Sure, the sticky spiral part is on average no bigger than your hand (3 to 7.5 inches in diameter)—and, alas, often at face height. But the outer frames can span almost 10 feet, which explains why the spiders are finally ready to build webs across hiking trails.
The purpose of the web, obviously, is to ensnare prey. If the web vibrates with a particularly big catch (i.e., bigger than 3 millimeters), M. gracilis proceeds with what’s considered a primitive method for spiders, evolutionarily speaking: It bites the prey first and only then wraps it in silk.
3. Trails where M. gracilis proliferates—and where it doesn’t
A trail’s web density in August and September will depend on hiker foot traffic and width/openness.
More webs:
- Rockywood Trail (Washington State Park)
- Whispering Pines Trail South Loop (Hawn State Park)
- Lewis Trail (Weldon Spring Conservation Area)
Fewer webs:
- Chouteau Island Levee Trail (Madison County, Illinois)
- River Scene Trail (Castlewood State Park)
- Chubb Trail (West Tyson County Park)
4. How to handle webs
If you’re hiking and blunder into their webs, the creatures will probably be OK, Bruns says. But hikers approach the webs in all kinds of ways. Here are three, from the least to most disruptive:
- Watch out and duck under. Sometimes the morning dew or angle of sun make the webs visible, and therefore, avoidable. You can also keep an eye out for the spiders themselves, which tend to rest in the middle of their webs from mid-morning to dusk, though spotting them can be difficult: Their black-and-white mottled abdomens blend in with the background.
- Follow the early-bird trailgoers. Usually by midday, someone has already moved through the space and taken one (or maybe several) for the team.
- Use the stick/branch method. Choose one shaped like a wide letter Y and hold it so the two tongs are out in front of your face.
Bruns says that he himself tries to leave them undisturbed whenever possible because of their ecological value: They themselves are eaten by bats and birds, and they keep fly and mosquito populations in check.“They’re the guardians of our landscape because they eat insects,” Bruns says. “If those spiders weren’t out there, we wouldn’t have forests.”
