Wild Ideas: Tiny aeronauts and gossamer bridges at dawn

Spiders build webs between trees, often yards apart, by jumping into the wind, attached by a single, strong filament of silk from their starting point. Pam Owen | Rappahannock News
Spiders build webs between trees, often yards apart, by jumping into the wind, attached by a single, strong filament of silk from their starting point.

This time of year I enjoy having my morning coffee out on my deck, which overlooks a small copse of trees.

I often start when light has yet to reach this side of the hollow, and before me is a subtle sea of green. I see some birds flitting around in the trees, but virtually no insects. But, on a sunny day, as soon as the sun crests the mountain on the other side of the hollow, it reveals thousands, of tiny, fairy-like creatures floating and flying in the air among a latticework of silken bridges — all backlit by the rising sun. In this ethereal light, I get an entirely different view of the natural world unfolding before me.

Some of the tiny aeronauts I see before me are mere bits of fluff riding the breeze, resembling seeds from an ash or cottonwood tree. But their insect biology is revealed as they change course, flying against the wind. Others larger, stronger insects with pronounced wings mover more assertively through the air — perhaps predators ending or just starting their daily hunting. With the light behind them, it’s hard to tell.

Two harvestmen meet at dawn.Pam Owen | Rappahannock News
Two harvestmen meet at dawn.

While the numbers of insects in the air is stunning, the most astonishing thing is the amount of silk filaments that create a latticework throughout the forest, bridging one tree or branch to another. The early morning dew magnifies each strand and makes it glisten. These bridges are the work of spiders, who jump into the wind to sail through the gaps, anchored by a thread of silk they attach to a tree or branch. Many times on a forest trail I’ve been startled by these bungee jumpers when they land on me from out of the sky.

In a Q&A in the science section of the New York Times a few years ago, science writer C. Claiborne Ray explained how spiders accomplish this amazing feat. Spiders that build orb-shaped webs usually start with a single “superstrength” strand, known as a “bridge thread” or “bridge line,” he writes. Spider silk is five times stronger than steel, and the strength of this line is believed to come from its telescoping protein structure. Ray describes how the spider stretches this thread from one point to another:

“First, the material for the bridge thread emerges from one of the spider’s specialized silk glands and is formed into a strand by its spinnerets. The loose end is drawn out by gravity or the breeze and allowed to blow in the prevailing wind, a process called kiting or ballooning. If the strand does not make contact with something and attach to it, the spider may gobble up the strand and recycle its proteins, then try again. If the gap is bridged, the spider reinforces the strand and uses it to start the web. A single bridge thread may be left in place overnight to mark a spider’s territory and a desirable starting spot for building a web the next day.”

The dawn light captures a web about 20 feet off the ground that a spider has anchored to two trees that are several yards apart. Pam Owen | Rappahannock News
The dawn light captures a web about 20 feet off the ground that a spider has anchored to two trees that are several yards apart.

One Madagascar arachnid, Darwin’s bark spider (Caerostris darwini), regularly bridges rivers through kiting. And kiting is not just used for bridging gaps when spiders construct webs. Spiderlings (the young) of some species also use this method to disperse from the nest. The thin strand of silk they spin to do this is usually referred to as “gossamer.” By literally casting their fate to the wind, they’ve been able to populate remote locations, even islands in the oceans.

Charles Darwin noted in his journal that the HMS Beagle, the ship he traveled on in his exploration of the fauna of the Pacific, intercepted clouds of spiders several times while in the bay of the Rio de la Plata. The ship was covered with gossamer, Darwin wrote, with the spiders lowering themselves from the rigging to the deck on the strands.

As I’m writing this, nature seems to be trying to bring the lesson home. A tiny spiderling just rappelled down from the roof eave above me on its own silk thread, passing within an inch of me and landing on the deck. It ran up the leg of the chair I’m sitting in, apparently thought better of it, and doubled back, disappearing under the deck.

The back lighting at dawn also also distorts the forms of creatures walking along tree limbs, making them seem larger and stranger. On a couple of mornings, what seemed like a huge spider with thin legs was ambling along a tuliptree limb not far from where I was sitting. Its manner of walking — slowly extending one leg after another in a lumbering grace that reeked of the primeval —  reminded me of the tarantulas that I’ve seen moving across the Mojave Desert. The invertebrate near my deck was not nearly so bulky and hairy but just as ancient. With light behind it and the moisture in the air, its size could be deceptive.

In revisiting the deck this morning, the same limb was host to a meeting of other smaller leggy arachnids, this time two harvestmen (in the order Opiliones, also known as “daddy longlegs”). Their meeting was brief, with each touching each other’s feelers before continuing on their respective journeys.

I usually revisit the deck in the evening and, while pleasant in the shade and with the evening bird song this time of year, I see no sign of the ethereal fairy world of dawn. The insects that emerged then are now seeking shelter for the night. And sunlight no longer illuminates what’s left of the spiders’ latticework, which they will reweave again after the sun goes down.

© 2015 Pam Owen


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