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Southwest Colorado has its cast of spiders; some are spooky, most are harmless

Warm homes are tantalizing to certain arachnids with winter on the way
Black widow spiders are misunderstood animals. While female widows pack a venomous bite and are potentially harmful to humans, they have a passive demeanor and prefer to stay out of the way of humans. They feed on bothersome insects such as flies and mosquitoes, lay their eggs in sacs along their webs and might venture into homes as fall arrives and temperatures drop, according to the CSU Extension Office. (Jerry McBride/Durango Herald)

Although store-bought decorative cobwebs are aplenty outside homes across Durango with Halloween less than two weeks away, the real deals might be waiting in a dark corner near you.

Southwest Colorado is home to a diverse cast of spiders and arachnids, including several iconic species such as tarantulas, the notorious black widow and bizarre-looking wind scorpions. Some species, such as funnel weavers, yellow sacs and even black widows are prone to navigating indoors when autumn arrives with cooler temperatures, according to the CSU Extension Office.

But that’s no reason to fret – most spiders in the Centennial State are harmless, said Ryan Schwarz, associate biology professor at Fort Lewis College. Even the western black widow, the most dangerous spider native to Colorado because of its potent latrotoxin (a neurotoxin used to paralyze prey), is a passive species unlikely to bite a human unless it is suddenly disturbed.

Instead of fearing spiders, Schwarz hopes people might take time to observe them and appreciate their beauty, like he did as an undergraduate at the University of Arizona.

A colorful goldenrod spider climbs around a plant in La Plata County. Southwest Colorado is home to a diverse array of spider species, nearly all of which are completely harmless, according to Ryan Schwarz, associate professor of biology at Fort Lewis College. (Jerry McBride/Durango Herald)
Ryan Schwarz, associate biology professor at Fort Lewis College, has studied long-jaw orb weavers for years. The spiders are common across the United States and make web nests in riparian areas near streams, rivers and other bodies of water such as Lake Nighthorse, he said. (Courtesy of Wiki Commons)

Schwarz hadn’t given spiders much thought. But when he had the chance to study a species known as the long-jawed orb weaver spider on the islands of Oahu, Maui and Hawai’i, his interest in the eight-legged animal sparked.

He remembered hiking through a Hawaiian forest at night to find and study the orb weavers. Rummaging through the brush in the dark of night for something less than an inch large might not sound like a fruitful activity, but it was the easiest way to find the them, Schwarz said.

“They have this eye shine, so if you are out at night with a flashlight and you shine it around, especially at the ground, you’ll see these sort of blue-green glimmerings sometimes. And those are spider eyes looking back at you,” he said.

Spider webs also glint in the dark when struck by light, which makes them fairly easy to locate, he said.

Schwarz would place the orb weavers under a microscope to observe their biology up close. That’s when he truly became fascinated with them, he said. The spiders were “beautiful”; their abdomens would gently expand and retract as they breathed.

“They have these specialized types of lungs called book lungs that they use for gas exchange,” he said. “So a really unique anatomy. Something you just don’t appreciate unless you get to look at them up close and personal like that.”

Long-jawed orb weavers belong to a family of spiders called Tetragnathidae that is widespread across the United States. They typically live along the edges of water in riparian environments and build their webs partway over the water’s surface. Orb weaver webs can be found among the rocks and shrubs at Lake Nighthorse and near creeks in the San Juan National Forest, Schwarz said.

They build their nests near water because that is where they will find their prey, mayflies and like insects that thrive near the water, he said.

“They’re very long,” he said. “When they get startled they stretch out their legs – half their legs forward and half their legs backward – so that they end up looking like a stick.”

Although the long-jawed orb weaver is “completely harmless” to humans, it might make a sore impression because of its long jaws and ferocious-looking fangs. But the long-jawed orb weaver is incapable of piercing human skin. While its jaws might look menacing, they are too thin and fragile to be a threat to humans, he said.

‘Bioblitzing’ for spiders

Schwarz has students perform what he calls a “bioblitz” for the conservation biology course he teaches at Fort Lewis College. The course is designed to introduce students to the biodiversity in and around Durango.

He tasks his students with searching out plants, insects and arachnids – often overlooked living things, he said.

The most common arachnid Schwarz’s students find is the tarantula, he said. In the fall, males become active in search of a mate. Females also become more active when they are hunting for prey; otherwise they remain with their burrows.

A tarantula crawls along the ground south of Durango. Tarantulas, while large, are docile toward humans. Males become active in the fall as they search for mates. They are among the most common creatures identified by Fort Lewis College biology professor Ryan Schwarz’s students during periodic ‘bioblitzes’ where they seek out wildlife native to Durango, he said. (Jerry McBride/Durango Herald)

He said Durango is the highest elevation he has personally observed tarantulas at and many more species live in tropical areas versus Colorado’s more temperate climate.

Tarantulas are gentle giants, he said. Although he doesn’t recommend that anyone pick up a tarantula they find in the wilderness – for the spider’s safety – doing so wouldn’t result in a bite.

“People see this big spider and think it’s going to attack them,” he said. “But they really have no interest at all in people and they’re happy to just go about their business. ... They just will meander right on by you. If you put your hand down by them they will stop and go around it.”

Tarantulas are by far the largest species of spider native to Colorado, but of all the native species that thrive in forests, outcroppings, gardens and kitchen room corners, jumping spiders are uncontestedly the cutest. At least, that’s what Schwarz has found.

Jumping spiders native to Colorado have two large forward-facing eyes surrounded by many tinier eyes in addition to small white hairs that make it appear as if the spider has a mustache, he said.

“They are really charismatic critters,” he said. “This is a spider that will look at you, they will see you. But they will not try and attack you.”

Jumping spiders have “incredibly” good vision and they utilize it to their best. They can perceive humans within about 6 inches away and will follow one’s finger if he or she dangles it before them.

“You can get them to track your finger movement. They’re very aware of you and very aware of your presence and the way you are moving,” he said.

Jumping spiders, while not rare to the Durango area, are a fun species for students to observe because they are small enough to avoid attention under most circumstances, he said.

Living with spiders

The western black widow, Latrodectus hersperus, is one of three North American widow species infamous for its orange to red markings that often take the shape of an hourglass on the underside of its abdomen. In humans, its venom causes severe pain at the bite wound and can lead to muscle cramps, abdominal pain, back pain and high blood pressure, according to a report published by The Permanente Journal, a peer-reviewed medical and social science journal.

A black widow climbs on its web Wednesday in Durango. (Jerry McBride/Durango Herald)

Schwarz said only female black widows, which dwarf their male counterparts, are potentially harmful to humans, and as with many spider species, he considers them more beneficial than threatening because they feast on mosquitoes, flies and other bothersome insects.

“I have quite a few spiderwebs in my house,” he said. “I’m just happy to check on them and see how they’re doing because they will catch those stray moths or flies.”

Black widows are easy to appreciate because of their jet black bodies juxtaposed with their bold red patterning, but other species also boast beautiful patterns and coloring, he said.

Diverse structure is one curious feature spiders possess, he said.

“Their eyes are very different from spider to spider. So the arrangement of the eyes can be really fascinating to look at. And the amount of hairs on their body will vary. Some will be very hairy like the tarantula, others will be less hairy and more sleek looking,” he said.

Sun spiders, also known as wind scorpions for their quick movement and active hunting style, are common to the Durango area and Southwest Colorado, Fort Lewis College professor Ryan Schwarz said. (Courtesy CSU Extension Office)

Colorado spiders present themselves in many colors and sizes with mixed hunting styles and habitats. The aptly named ground spider prefers to hide out in webbing under logs and stones and only comes out to hunt; wolf spiders forego webs and actively chase down their prey, similar to sun spiders or wind scorpions, which are non-spider arachnids with swift feet and strong jaws that they use to capture and kill large prey like beetles and spiders.

Schwarz said he wishes more students took an interest in studying spiders; arachnids, much like insects and other buggy creatures, are understudied when it comes to researching how life on Earth developed and how the impacts of climate change can change life’s course.

He said people should consider inspecting the next spider they come across with a magnifying glass.

“Just take a minute and appreciate them. Lots of people like to bird watch, and birds are beautiful, granted, but they’re also a lot easier to see,” he said. “But if (someone) was willing to stop, kneel down and take a look at spiders, they’d see as much beauty if not more in those little critters.”

cburney@durangoherald.com

An earlier version of this story misspelled Ryan Schwarz’s last name.

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