Introducing the Slingshot Spider

(YouTube link)

Jeff Cremer of the Tambopata Research Center in Peru (the folks who found the tower-building spiders) sends us this video of a peculiar spider doing something very strange. It's using its web as a slingshot! This aggressive behavior enables the spider to capture insects, like mosquitos, that have developed strategies for not getting caught in a web. The spider belongs to the family Theridiosomatidae, commonly known as ray spiders. This particular spider may be the species Naatlo splendida, or else a new undescribed species.

Want to see the spider up close? Continue reading for photographs and some FAQs from the crew that found and photographed it.

(Image credit: Lary Reeves)

When and where did you discover this?

University of Florida entomologist Lary Reeves: One muggy night in May 2013 at the Los Amigos biological station, I was slogging through a swamp with Geoff Gallice and Lindsay Whelan trying to get my hands on a couple of juvenile spectacled caiman, and dodging bullet ants on the foliage. I think I was watching for bullet ants when I noticed a web that was pulled back from the center, making a cone, and a spider in the web, holding the web in a tensed position along an anchor line. I looked at it a little closer, called everyone else over, and presumed that the spider released the tension in the web to capture prey. As soon as the words left my mouth, a mosquito flew by and the spider slingshotted towards it.
Biologist Phil Torres: This population of spiders we filmed was first found by graduate student Troy Alexander several months ago. This behavior is not very well known or documented, so we set out to try and capture photos and video for follow up research on the subject.
Who discovered them?

Torres: These types of spiders were originally described about 80 years ago. They are an obscure group, very tiny, not very well known, and there are likely a lot of new species out there that have not yet been named. This particular spider appears to be a good match for the species Naatlo splendida, but we would have to collect it to be sure.
How exactly does it work? How does it get such force?

Reeves: The web is similar in design to other orb webs - the two dimensional webs you might find in your garden, or built at night on the eaves of houses to capture flying insects. The big difference is that the center of the web is anchored to the surrounding vegetation by a line that extends from the central hub to the anchor point. The spider, like the orb weavers most people are familiar with, sits in the center (the hub) of the web. From there, it stretches the web towards the anchor point by crawling towards it and holding the bundled up slack in it's legs. It's possible that the hairs on the spiders body are sensory, and tuned the the frequency of a fly's wingbeats. Regardless, it somehow senses that a fly has come within reach of the web and releases the tension on the anchorline, propelling the web and the spider towards the prey. If the spider misses, it seems to be able to reset the web/trap fairly flawlessly and with great ease.

Torres: The spider builds a fairly normal web, but it has a sort of draw string attached from the middle of it to a nearby solid surface. It is able to very quickly pull on that string and bundle it up, which ends up pulling the entire center of the web off to the side. This action builds up a tremendous amount of tension from the web stretching into a cone like that, so when the spider is triggered by something landing in or right near its web it quickly releases and the web goes flying into the prey, making it much more likely to get tangled.

(Image credit: Jeff Cremer)

Is this the first time you've ever seen a spider behave like this?

Reeves: Yes - but I've seen enough spiders employing complex web designs and other unexpectedly clever prey capture techniques to not be terribly surprised by this. I think without knowing of spiders like the ogre face/net casting spider, bolas spider, decoy spider, etc, I wouldn't have thought twice about this web.
Torres: This was a first for me. My colleague Lary Reeves who was with me on this expedition had seen it once before and he too was curious to document it further. Spiders do so many odd behaviors, so this was one of many amazing things we were able to document.
How is it better or worse than a normal web? Is it a more effective way of catching prey?

Reeves: I don't think that it's necessarily better or worse than any other web - I think it's just specialized. All the examples of this that I've seen so far have been in vegetation directly above standing water, or in close proximity to it. It seems to me, that these spiders are specializing in capturing freshly emerged flying insects, likely flies or small mayflies, as they emerge from the water to disperse. Assuming they are specialists on flies that use water as a larval habitat, it makes sense that they would use this technique if it is superior to having a less dynamic web for catching these prey items.

Torres: Other spider webs may be more limited in how they entangle their prey- they are reliant on how sticky their web is, combined with the flight of the prey impacting the web. This method of flinging the web appears to make it much more likely that the prey will get tangled, as they seem to be getting slammed into sticky web regardless of the prey's original flight speed. Imagine the difference between bumping into a sticky trap and having a sticky trap flung at you.

(Image credit: Jeff Cremer)

How was the picture taken?

Photographer Jeff Cremer: I used a Canon 6D and 7D with couple of different macro lenses to get the shot. I used a Canon 100mm macro as well as a special Canon MP-E 65mm lens.

It was a fairly difficult shot to get. We were in the middle of the amazon jungle, in the middle of the night and standing in about 50cm of water with mosquitos flying.

I have big Gitzo tripod that I use for my 600mm f/4 lens.  It has a big tripod foot that I am able to slide back and forth so I used that as a makeshift focusing rail to help me find the spider and focus on it.
Once I found the spider and focused on it I locked everything down, set the ISO to about as high as it would go and started filming at 60 frames per second.  We used only a flashlight to light the subject.

An article at Wired describes an outing to find the spiders.

Tinier than your pinky fingernail, they spin a web that’s only about three inches across, and is usually tucked beneath some leaves or nestled near a tree trunk. The spiders then stretch the web into a narrow cone shape by crawling down a dragline near the web’s center. As they crawl, they reel in the dragline silk, ending up with a clumpy, bunched-up thread clutched between their four front legs. When the spiders sense the vibrations caused by insects, they release the dragline and in a microsecond send themselves – and the web – catapulting toward their prey.

-Thanks, Jeff!

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Intriguing. Could be a thesis for someone who had years to lug audio equipment and a magnifying glass around the Peruvian jungle. And who doesn't mind spiders. And could get the funding.
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The spider is situated 'backwards' on the web, which makes re-setting the slingshot easier. I' imagine that the spider uses sympathetic vibrations of the web itself to detect the sound coming from the insect's wings.
It would be interesting to see if the construction of the web, perhaps the length of the strands or their tension, are attuned to the particular range of sound coming from prey insect wing beats. If there were more spiders of this sort, with special preferences for certain insects, I'd predict that their webs would reflect these preferences by being constructed to better detect sounds of the preferred frequencies.
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