Tetragnatha | spiderbytes

This post features photographs by Sean McCann. For more beautiful photography and natural history of arthropods and other wildlife, check out his blog, Ibycter.com.

As a sequel to our recent encounter with some long jawed orb-weavers in the genus Tetragnatha (the tiny and cryptic Tetragnatha caudata), this week on an evening walk at Iona Beach, Sean and I observed some neat predation and mating behaviour in another species, most likely Tetragnatha laboriosa.

We made our first observation just as the sun was beginning to set, the beginning of the most active hunting hours for Tetragnatha laboriosa. This female had just captured her first meal of the evening, a bug in the family Miridae.

After biting it, she began wrapping it with silk, which she pulled out of her spinnerets with her last pair of legs (you can see her caught in the act below).

After wrapping the bug lightly with silk, she carried it back to the hub of her orb web and settled down to dine.

Unfortunately for the spider, dinner was interrupted by Sean’s efforts to get a good photograph. The disturbance prompted her to drop her meal and retreat to the vegetation at the edge of her web. Isn’t she just gorgeous?!

After a minute or so, she went back for her abandoned prey.

She then carried it off the web to resume her meal in peace. You can see from this image how the lovely coloration of these spiders allows them to blend in with plant stems when they adopt their cryptic stick-like posture.

Later, when the sun had all but set and we were just about to head home, Sean spotted a pair of spiders (probably the same species, T. laboriosa) mating in a female’s web.

Mating involves a fair bit of contortion for long jawed orb-weavers. Below you can see the male’s extremely long pedipalp (one of a pair of appendages modified for transferring sperm) engaged with the female’s epigyne (genital opening). The male’s short third pair of legs is used to position his partner’s abdomen. Throughout copulation he maintains a firm grip on the female’s jaws with his own.

Here is a closer look at the mating position, where if you look closely you can see one of the female’s fangs interlocking with the special tooth on the male’s corresponding chelicera.

Here is a drawing by B. J. Kaston of what the cheliceral embrace looks like close-up. The male, with larger jaws, is below, and the female above.

Fig. 876 from Kaston 1948. Interlocking jaws of Tetragnatha pallescens (which looks very similar to T. laboriosa) during mating.

The female’s fangs get locked in underneath the special large tooth that protrudes from each of the male’s chelicerae.

As if we hadn’t had enough excitement already with the chance to closely witness such an intimate encounter, moments later we spotted two additional males waiting in the periphery of the female’s web. We were in for quite a show!

Here is one of the males that was waiting in the wings, posing elegantly and displaying his long jaws and even longer pedipalps. We’ll call him bachelor #2.

Not long after we spotted them, one of the lurking males made his move, lunging at the mating pair with his jaws held wide.

A bit of a tussle ensued, after which the mating spiders disengaged. The attacking male pursued the mated male off the web and all the way to the substrate below. The female, apparently rather perturbed by this rude interruption, also left the web. One of the two rival males, apparently dominant, soon ascended back toward the web via his dragline.

Just as the winner of the first brief battle returned to the web, the third male entered the ring, and a second chase ensued. This cycle repeated a couple of times, until at last only one male returned victorious to the periphery of the web.

Bachelor # 2 (or was it #3?) settled down to wait at the edge of the web, while the female made her way back to the hub.

It turns out that female T. laboriosa only mate once as a rule, and if copulation is interrupted as we observed, it’s a toss-up whether or not she will be willing to pick up where she left off (LeSar & Unzicker 1978). We couldn’t stay to see if our champion was able to successfully mate, but we wished him the best of luck!

Iona beach, near the Vancouver International Airport in Richmond, BC, is fantastic place to go looking for spiders and other arthropods, and there always seems to be something new to discover on the dunes. So it was an unusual situation when last Friday evening, just before the park gates were about to close, Sean was lamenting not having found anything very interesting to photograph. We decided to spend our last minutes on the beach in an effort to turn up some sleeping hymenopterans in the vegetation bordering a walking path. After closely inspecting a couple of plants, instead of a sleeping bee or wasp, I found what at first glance looked like a tiny twig hanging in the middle of a spider’s orb web. Meet Tetragnatha caudata, the longest, most cryptic orb-weaver I have ever met!

This slender female was not easy to spot among the grasses, even though she was hanging right in the middle of her web. Her body is only about 1cm long from tip to tail.

Tetragnathidae is the family of the longjawed orb-weavers. You can see where the name comes from in the photo of a male below. During mating, the male and female interlock their large chelicerae in toothy embrace. This is where the male’s exceptionally long pedipalps come in handy, allowing him to reach the female’s epigynum while maintaining his hold on his partner’s fangs.

You can see this male’s large, powerful jaws sticking out to the sides underneath his very long, slender pedipalps.

Spiders in the genus Tetragnatha are sometimes called ‘stretch spiders’ because of their elongated bodies. They often rest with their first two pairs of legs stretched out in front. They can be very cryptic in this posture, especially if they cling to twigs or stems that are similar in colour to their bodies. Although they normally use their webs for hunting, sometime Tetragnatha will also snap up unsuspecting prey when lying low like this on vegetation.

A male Tetragnatha in camouflage mode. This works better on dry grasses or twigs, I would think. But still pretty stealthy here.

Most species in the genus Tetragnatha are difficult to tell apart, but I got lucky with this one (it keys out in the second couplet of the key to the Canadian species in this genus). Tetragnatha caudata is so named because of its strange looking abdomen (caudata means ‘tailed’ in Latin). While I would expect the spinnerets to sit at the tip of a spider’s abdomen, in this species there is a slight kink where the spinnerets sit on the underside of the abdomen, and a pointy tail sticks out behind them.

If you look closely you can see a strand of silk coming out of this female’s spinnerets, located on the underside of her abdomen just before it bends into a pointy tail.

The orb webs of Tetragnatha are usually horizontal or angled (unlike the vertical webs of spiders in the more familiar orbweaver family Araneidae) and have a hole in the centre where the spider sits waiting for prey.

We found several of these tiny Tetragnatha caudata among tall grasses, but larger members of the genus typically build their horizontal orbwebs over water, allowing them to capture insects such as mosquitoes as they emerge.

So let this be a lesson: next time you’re out looking for wildlife, stop and take a careful look in some seemingly boring vegetation! You never know what wonders you might turn up.

Thanks to Sean, as usual, for the great photos!

References:
Adams, R.J. (2014) Field Guide to the Spiders of California and the Pacific Coast States. University of California Press, Berkeley and Los Angeles.

Bradley, R. (2013) Common Spiders of North America. University of California Press, University of California Press, Berkeley and Los Angeles.

Dondale, C. D., Redner, J. H., Paquin, P., & Levi, H. W. (2003). The Insects and Arachnids of Canada. Part 23. The Orb-weaving Spiders of Canada and Alaska (Araneae: Uloboridae, Tetragnathidae, Araneidae, Theridiosomatidae). Ottawa, NRC Research Press.

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Long, cryptic spiders