Tetragnatha revisited: dinner and romance at sunset

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.IMG_1953

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). IMG_1956

After wrapping the bug lightly with silk, she carried it back to the hub of her orb web and settled down to dine.IMG_1962

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?!
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After a minute or so, she went back for her abandoned prey.
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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.
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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.
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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.  IMG_2106

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.jaws_clasping

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.

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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.  tooth_landscape

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. IMG_2120

Not long after we spotted them, one of the lurking males made his move, lunging at the mating pair with his jaws held wide.  IMG_2108

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. IMG_2112

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.IMG_2129

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.     IMG_2140

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!IMG_2138

The mystery of the burrow-dwelling sand dune spider

On a walk at Iona Beach a couple of weeks ago with Sean (who kindly provided all the photos that follow) I came upon a small hole in the sand, and after poking at it a bit, realized it was a silk-lined burrow with what looked like a trap door. We tried to figure out who lived there, but didn’t find anyone inside.

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The mystery burrow where this natural history adventure all began!

I went home puzzling about the mysterious burrow-dweller, and emailed our local spider expert Robb Bennett to see if he had any idea what kind of spider the owner might be. His response that it was probably a wolf spider burrow came as a surprise to me. I don’t know a lot about wolf spiders (family Lycosidae), and although I have occasionally seen them hunkered down in shallow depressions under stones and logs, I wasn’t aware that many species build quite elaborate silk-lined burrows. As it turns out, some lycosids overwinter or oviposit in burrows, or hunt by waiting just inside the burrow entrance for prey. One genus, Geolycosa, spends almost its entire life underground, in burrows up to 17cm deep (Dondale & Redner 1990)!

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Before this mystery began, I had only seen lycosids associated with shallow burrows, like this one we found on Mt. Tolmie.

A few days later, we returned to the beach to look for more spiders and other arthropods. We encountered several jumping spiders, including this one.

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 A Sitticus male?

After a while, Sean spotted this beautiful and well-camouflaged male wolf spider.

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After being disturbed, this spider alternated between lightning-fast sprints and freezing with its legs splayed out against the sand. It takes full advantage of its banded legs and mottled body coloration, which allow it to all but disappear against the background!

Next we encountered two females of the same species carrying their spiderlings on their abdomens. Lycosid females have special abdominal hairs onto which the inner layer of spiderlings cling (Rovner et al. 1973).

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The second female we found had a smaller brood of larger spiderlings hanging on mainly to the underside of her abdomen.

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Here’s a portrait of the same female as the previous photo, this time showing the characteristic lycosid eye arrangement.

A little while later, much to my excitement, I came across another silk-lined burrow!

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Another mystery burrow, very similar to the original!

Using a bit of dry grass to scratch at the sand-covered silk surrounding the burrow entrance, I was able to entice the resident spider towards the opening. And just like that, the mystery was solved! The burrow belonged to a female of the same wolf spider species we had been running into all evening as we explored the beach.

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The spider soon approached the entrance of her burrow to investigate the source of the disturbance.

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After some more serious disturbance resulting in the opening of the burrow now looking a lot more like the (also disturbed) entrance of the original mystery burrow, the spider was persuaded to come out entirely.

After a successful evening of sleuthing, we went home and identified our cryptic burrow-dwelling spider as Arctosa perita. This species is typically found on sand dunes or sandy heathland, and only the females construct silk-lined burrows (Dondale & Redner 1990). It is introduced to North America, and is apparently only present in certain areas of southern British Columbia. The similarly coloured beach wolf spider Arctosa littoralis (beautifully photographed by Ted MacRae here) is native to North America.

The burrow entrance can be cinched up and made effectively invisible to humans, but this does not prevent some predators from detecting the spiders inside. In Britain, Arctosa perita is the preferred prey of the spider wasp Pompilus plumbeus, which uses a combination of smell and touch to locate the spiders within their burrows (Bristowe 1948). This spider (and other lycosids) can detect polarized light, and this species is somewhat famous for being able to navigate using the sun or the moon (references in Dondale & Redner 1983).

Arctosa perita doesn’t seem to have a well established common name, but I found it referred to as the ‘sand bear-spider’ by Steven Falk on Flickr (check out his lovely photo set), which I quite like. The genus name Arctosa is based on the Greek word for bear, ἄρκτος (arctos). The species name ‘perita‘ means ‘mountain dweller’ in Greek which doesn’t make a whole lot of sense unless you consider the sand dunes that are apparently the preferred habitat of this species to be very small mountains. I will now always think of it as the mysterious burrow-dwelling tiny sandy mountain bear-spider! Catchy, right?

Bonus fun fact about wolf spider names:

The type genus is Lycosa, which of course means ‘wolf’. Several other genera were subsequently named to rhyme with Lycosa, with the names based on other carnivorous animals: Alopecosa (fox), Crocodilosa, Dingosa, Hyaenosa, Lynxosa, Mustelicosa (weasel), and Pardosa (leopard).

References:

Bristowe, W. S. (1948). NOTES ON THE HABITS AND PREY OF TWENTY SPECIES OF BRITISH HUNTING WASPS. Proceedings of the Linnean Society of London, 160: 12–37. doi: 10.1111/j.1095-8312.1948.tb00502.x

Dondale, C. D., & Redner, J. H. (1983). Revision of the wolf spiders of the genus Arctosa CL Koch in North and Central America (Araneae: Lycosidae)Journal of Arachnology, 11: 130.

Dondale, C. D., & Redner, J. H. (1990). The insects and arachnids of Canada. Part 17. The wolf spiders, nurseryweb spiders, and lynx spiders of Canada and Alaska. Araneae: Lycosidae, Pisauridae, and Oxyopidae. Publication-Agriculture Canada (English ; 1856).

Rovner, J. S., Higashi, G. A., & Foelix, R. F. (1973). Maternal behavior in wolf spiders: the role of abdominal hairs. Science, 182: 11531155. doi: 10.1126/science.182.4117.1153