A couple of years ago a budding young behavioral ecologist made an interesting discovery when she sat down to rest on a hike in Bridger-Teton National Forest. In some gravel near her boot toe was a spider actively building a mound of little rocks, a behavior not previously known.

Maggie Raboin had just discovered mason spiders (Castianeira teewinoticus), unique spiders that build mounds, not construct webs or burrows.

Maggie, a graduate student at the University of California, assumed everyone knew about mound-building spiders until she started asking her colleagues. When no one knew of such, it dawned on her that she had a new species. With a partial grant from the Meg and Bert Raynes Wildlife Fund, she spent a summer here investigating the unique behavior of this new species. She filmed 41 of 711 mounds being built, most actively from 7 a.m. to 2 p.m. in early August, only to see the mounds destroyed by an intense thunderstorm, which exposed the once-protected egg sacs. There goes research sometimes.

Her experience makes one wonder: How many of us have witnessed a new species or unique behavior assuming everyone knew about it already?

Here is an old observation of the more common behavior of spiders’ web making, pulled from my July 11, 1990, column in the Jackson Hole News.

See something, say something

Spiders. I cannot honestly say I’m fond of spiders, yet I do admire them. They’re successful little creatures, going diligently and patiently about their business.

Their presence, their abundance, their variety, usually get noticed most on early, humid mornings when their bedewed webs are displayed against the slanting sun. There are vertical webs, off-center webs, horizontal, ground-hugging ones. No doubt there are many, many more variations I’ve never noticed.

A few weeks ago I was sitting quietly, just sensing the pace of an early morning when a shaft of sunlight illuminated a spider’s web constructed to cover a burl in the trunk of a fir tree, over one of those wounds left when a lower limb falls. There was a struggling victim in it which the web’s owner was busily encasing. When the web was out of direct sun, I could not discern it.

At a distance I speculated about this spider stuff for a bit, thinking that it’s not Nature’s way that a successful family of animals, one with many varied members, would depend on its hunting on having prey simply blunder into its trap. That’s not an approach which makes a family succeed for it doesn’t reward skill or adaptation. Far too chancy.

Now comes an observation which helps me. Probably you know this, as all my faithful readers are knowledgeable, well-read and all-wise. But, in case you missed it, Catherine Craig and Gary Bernard, Yale University and University of Washington respectively, writing in Ecology, have shown that common garden spiders weave webs which look to an insect like flowers. These spiders use designs to lure insects. Why, certainly. Obvious, if you knew how to look.

Get this. Insects that feed on pollen and nectar are sensitive to ultraviolet light. Some spiders, Craig and Bernard found, weave webs from silk that reflects very little ultraviolet light — shortwave radiation which you and I cannot see — and then add designs to that basic structure with another, a different silk which does strongly reflect UV light. And these designs, — which you have already guessed, you smarties out there — are similar to patterns which are reflected — in UV light — from many flowers. Slick.

More than that. The bodies of these dang spiders reflect UV light, making an additional lure. (Is that why they hang out in different places in their webs?) These experimenters showed that “decorated” webs with the spiders present capture over 50 percent more insects than is the case with empty, undecorated webs.


Field notes: Neighbors along Wenzel Lane in Wilson reported various sightings this week.

Family groups of eight to 24 magpies gathered on wires and fence rails, sweeping into newly mowed fields, feasting on exposed rodents, snakes, insects. Geese appeared in numbers.

A thumbnail-sized chorus frog, found on a walkway after Tuesday’s hailstorm, quickly disappeared into a garden. A young weasel — long or short-tailed — was spied leap-running into ditch and along fences. An adult long-tailed weasel was seen two days later in another Wilson yard, and unfortunately two dead on Highway 22.

A family of flying squirrels was reported anonymously. A great horned owl got one. A Williamson’s sapsucker, male in molt, perched atop a dead aspen.

John Wilbrecht saw a dozen blue geese (a form of snow geese) fly in a long line heading south over the Stilson parking lot.

Standing by a side channel of the Snake River near the Bar-B-C, Mark Huffman was impressed by a flotilla of 14 juvenile mergansers escorted by a large female — a good mother!

Deb Patla reports tiger salamanders are doing well this year.

Dragonflies were seen in numbers up on top of Grayback Ridge above Hoback by Susan Marsh and Frances Clark. Many people have commented on recent increases in mosquitos, flies and butterflies. Earwigs, too. Do fly pollinators bite or biting flies pollinate? A question to research.

Farther afield in Yellowstone National Park, Bernie McHugh saw eight Western grebes, one eared grebe, and one red-throated grebe, among dozens of lesser scaup, 25 golden-eyes, eight ring-necked ducks, 10 adult and 25 juvenile buffleheads, and 10 white pelicans, all nonbreeders, at the outlet of Pelican Creek into Yellowstone Lake on July 17. He reports black rosey finches feeding on insects and possibly seeds amid abundant alpine wildflowers on the Beartooth Highway.

Bert Raynes writes weekly about whatever suits his fancy with a dash of news on nature. Contact him at columnists@jhnewsandguide.com.

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(1) comment

Rick Mulligan

Pretty neat stuff.

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