BOLAS SPIDERS

I'M CHARLES E. HUTCHINSON'S biggest fan. Now, I never met the guy, nor know anything about him. But he was the first to see, describe, and understand something that no one else had: the hunting behavior of a female bolas spider.

A Little Background: The decades surrounding 1900 mark the Golden Age of Nature Study, when sophisticated folks pursued the honorable past-time of observing and recording the natural wonders around them. So Mr. Hutchinson sat outside for days, notebook and sketchpad in hand, carefully watching an odd-looking female spider and noting every nuance of her behavior. She obviously belonged to the orb weaver family-a group well known for its fancy webbery-yet she constructed no web at all. And during daylight hours she simply didn't move, resting openly on the top side of a leaf, cleverly (and safely) disguised as a fat glob of bird poop.

Now the Good Stuff: At nightfall, his subject got incredibly busy. First, just like Walt Whitman's noiseless, patient spider, she launched forth filaments out of herself, "ever tirelessly speeding them" to form a sturdy line, a few inches across, between two branches. Shifting to the middle of her "trapeze," she then created another thread, this time adding what Hutchinson called "a very small quantity of viscid matter," working and reworking it with her spindly legs until it resembled a sticky ball or pendulum, which she dropped into the free space below. To complete the circus motif, she finished her act by hanging sideways, grasping the horizontal line with two of her left legs, the weighted vertical line looped between her mouth and right foreleg.

Continuing with Hutchinson's elegant and precise prose, recorded in a 1903 article ("A Bolas-Throwing Spider") in Scientific American:

If the writer's description is clear, the reader now perceives the spider holding in its hand, as it were, a line to the lower end of which is attached a globule, the whole forming a most singular and ingenious contrivance designed for a useful purpose. . . . If now the observer is to be rewarded, he will see, by the light of the moon, a large moth approaching, flying slowly along as though searching for something. . . . As the insect comes within [a] carefully measured limit, the spider draws back the bolas-supporting leg and, with a pendulum-like movement, swings it rapidly forward in the direction of the moth. The bait is directed with almost unerring aim and finds lodgment on some portion of the victim. In nearly every instance, it strikes a wing, a part to which it is probably particularly directed. . . . The moth, finding itself fast, flutters violently in an attempt to free itself, but the assailant drops quickly down from its trapeze and sinks its fangs into a vital part. . . . By reason of the poison injected, the moth is soon paralyzed, after which it is carefully enswathed in bands of silk.

Wow! A spider hanging by two legs, swinging a sticky weight or "bolas" like an Argentine cowboy, ensnaring, paralyzing, and then trussing up her victim (to be eaten later) in a silk straitjacket. There in his own backyard, Hutchinson struck the mother lode of Nature Study. His meticulous, painstaking work and vivid descriptions were commemorated fifty years later by the naming of a newly discovered bolas spider, Mastophora hutchinsoni. (Less seriously, a sports-nut-turned-arachnologist called another species M. dizzydeani: "Since the spider's livelihood depends on throwing a ball fast and accurately, it seems appropriate to name it in honor of one of the greatest baseball pitchers of all time.")

But Here s What I Love Most: After accurately describing what he had seen, Hutchinson pondered The Why of it all, and then predicted exactly what later researchers would discover. Why, for example, would any reasonably intelligent, self-respecting moth be attracted to a dangling medallion of doom? Hutchinson concluded his paper by stating that "in view of the limited number of moths ordinarily about . . . and the almost unfailing success of the spider in making a capture during the night," a scentless (to us humans) but "agreeable" odor must attract the prey.

The Prediction Fulfilled: Hutchinson's hypothesis hung in limbo until 1977, when another keen observer added this to the puzzle: Only male moths zero in on the bolas, and only from downwind. Then ten years later, biochemists proved that bolas spiders produce compounds identical to lepidopteran sex pheromones. That's right! Females practice the most dastardly deception ever devised, tricking innocent male moths-just out cruising for a good time and minding their own business-by mimicking the scentless scents that they seek. Spiders swallow and reform the bolas frequently during the night (another of Hutchinson's original observations), thus renewing its viscidity. Why not also change its "flavor" to better fit expected prey species-like, "early" pheromones for dusk-flying types, and "late" ones for the midnight crowd? And why not make seasonal changes as well, to catch bigger critters as you grow bigger? Such utter evil! (At least from a fellow male's perspective . . . .)

So I salute you, Mr. Hutchinson. You were the first to see it, and the first to make sense of it, and then you correctly predicted what other scientists would conclude about it. Good work, sir!

Larry Davenport teaches biology at Samford University.

Copyright University of Alabama Press Winter 2004
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