Bait scent, fishing-line device allow spider to reel in moths

A toadlike bolas spider holds her silken weapon: a sticky ball she dangles and flings at approaching moths.

Columbus Dispatch

October 2, 2016

NATURE

Jim McCormac

A gaucho is a cowboy of the South American pampas. Gauchos are skilled horsemen and effective wielders of an odd weapon known as a bolas. The bolas is a stout cord to which they affix a heavy ball or balls. When hurled accurately, the bolas ensnares the legs of quarry and trips it up.

A group of spiders has been flinging bolas lines far longer than the gauchos.

The bolas spiders comprise a group of about 50 species, all of which occur in the Americas. Thirteen species are found north of Mexico, and four occur in Ohio.

Finding a bolas spider is always a big deal. They’re rare and easily overlooked. It wasn’t until Sept. 3 that I finally clapped eyes on one of these bizarre spiders.

I and others were conducting nocturnal field work in The Nature Conservancy’s sprawling Edge of Appalachia Preserve in Adams County. Suddenly, a roar went up from David Hughes, who is a firefighter and expert photographer. He had found a toadlike bolas spider, Mastophora phrynosoma.

During the day, the toadlike bolas spider rests atop a leaf, looking like an amorphous glob of fungus or gooey bird dropping. From certain angles, it looks rather toadlike. Presumably, would-be predators ignore such an unpalatable-looking mass.

Come dusk, the spider spins a few silken guy wires under leaves and prepares to hunt. She hangs from her support lines and crafts her sophisticated weapon. By rubbing a silken line against sticky secretions generated by her spinnerets, the spider forms a gluey ball.

When all is ready, she suspends the sticky bolas from a silken strand and holds the line with one of her forelegs. The look is much like a fisherman holding a baited rod.

She then emits a fragrance that mirrors pheromones secreted by a certain group of female moths. Eventually a male moth will detect this pseudopheromone and fly in to investigate.

As soon as the amorous moth comes within striking range, the spider flings the bolas and snares the moth. The duped victim is reeled in, dispatched and eaten.

The much-smaller male spiders and young females do not hunt with a bolas. Remarkably, they produce a scent that attracts tiny moth flies, which are seized and eaten.

Lots of weird things transpire under cover of darkness.

Naturalist Jim McCormac writes a column for The Dispatch on the first, third and fifth Sundays of the month. He also writes about nature at www.jimmccormac.blogspot.com.

Two supremely cool spiders: Arachnids one seldom sees

Ohio Brush Creek, as seen early on a misty morning, last Sunday, September 4. This stream is the epicenter of the sprawling Edge of Appalachia Preserve, owned and managed by the Ohio Chapter of The Nature Conservancy, in partnership with the Cincinnati Museum Center. The preserve's 16,000+ acres in Adams County contain some of the richest biodiversity in the Midwestern United States.

Last Saturday, I joined spider expert Richard Bradley, along with John Howard and Laura and David Hughes, for an epic natural history excursion. We were after a rare beetle (got it, check), and a couple of rare spiders. Along the way, we found scads of interesting flora and fauna, but I will confine this post to two supremely cool spiders, both of which were brand new to me.

Shortly after we entered a sun-baked prairie opening, sharp-eyed Laura Hughes spotted this barely discernable aberration in the soil. It's the circular cap in the exact center of this image, sort of like an earthen manhole cover. Even though we knew what to look for, it was an amazing spot, as the lid blends with its surroundings almost to perfection.

We carefully opened the lid, which is held in place with a silken hinge. The little stick on the right props it open, and reveals the smooth hole below, which is a few inches deep.

And here is the occupant, a rarely seen Trapdoor Spider, Ummidia adouini. Rich had received a report and photo of one of these some time back, from this general area. Given that actually finding the burrow is a bit like finding a needle in a haystack, we felt good about locating this, and rather quickly, too.

The spider returns to the depths of its lair. We teased it out with a pipe cleaner in order to admire the animal and make some photos. It's a decent-sized spider, but not overly big - it would probably mostly cover a nickel.

The hunting technique of a Trapdoor Spider is beyond awesome. At night, it comes to the summit of the burrow, and pushes the trapdoor open ever so slightly. When prey wanders near - small insects mostly - the spider erupts  from its burrow with blinding speed, and pounces. The victim is blanketed by the spider's large forelegs, and quickly pulled back into the burrow where it will be eaten. If all goes smoothly, the entire attack sequence, from trapdoor popping open to spider bursting forth to prey disappearing back into the burrow, takes just a second or so.

Here's a great video of a Trapdoor Spider in action: CLICK HERE.

The next cool spider was an unexpected bonus. We were searching for various nocturnal creatures about 1 am on Sunday morning, and were making a last round of a very interesting area before packing it in. Suddenly a shout went up from Dave - he had found an amazing spider that we had long wanted to see. In this distant photo, it looks just like a bird dropping on one of the leaves of this redbud. I made this image later that morning, after the sun had risen and the spider went into resting mode for the day.

And here she is, the Toadlike Bolas Spider, Mastophora phrynosoma. Strange indeed. This shot is of her at rest, head on. Her head is interesting, with its bidentate "horns", and she tucks her forelegs neatly around her face. In real life, the effect is quite remarkable and it takes a while to realize what one is looking at, and which end is which. The spider really looks like an amorphous glob of something decidedly unpleasant.

The real magic of this amazing spider takes place at night. This is her, shortly after Dave discovered it. The bolas spider runs a few silken struts from the leaves of her host tree, and dangles from those. She then releases a "bolas" line (a bolas is a weapon of South American origin; a strong line with a ball or balls attached. It is thrown at an enemy and entangles their limbs). The liquid droplet at the end of the bolas is very sticky, and most amazing secretes a fragrance that is a near exact match for the pheromones of a few species of moths.

When one of these moths flutters in to investigate the source of the pseudo-pheromone, the spider deftly swings the bolas and snares it. The moth is then reeled in and eaten. I would love to be able to stake one of these spider out long enough to observe - and hopefully photograph - a kill.