Rhomphaea: ridiculously long theridiids

RhomphaeaFictilium2

Male Rhomphaea fictilium – a theridiid with a ridiculously long abdomen and pedipalps! Photo: Al Denesbeck (used with permission).

I’ve written about long spiders before: the “stretch spiders” in the family Tetragnathidae (long-jawed orb-weavers) are notable for their elongated bodies as well as their long jaws. When I first spotted Rhomphaea, I thought it might be a tetragnathid, before taking a closer look and realizing it must be something else entirely. As it turns out, Rhomphaea is a very odd-looking member of the family Theridiidae, or comb-footed spiders, which includes the black widows!

081015IMG_6437

Rhomphaea fictilium from my field site at Island View Beach on Vancouver Island, BC. This spider does not show much resemblance to its relatives the black widows, who are found nearby! Photo: Sean McCann (used with permission).

Rhomphaea is a Latin word of Thracian origin that literally means long spear or javelin. The long, straight abdomen of the male in the photo below helps explain the name.

Rhomphaea_male_KyronBasu

Male Rhomphaea fictilium with long, “spear-like” abdomen and extremely long pedipalps. Photo: Kyron Basu, licensed under CC BY-ND-NC 1.0.

Below is a female Rhomphaea projiciens with her egg sac. Note that the spider has a tiny spine on the end of her abdomen, making it more literally spear-like!

P0L090R0G0CRZQNRYKNRLQNRLQURG0CQ20Q0SQCR0QR07Q00IQVRMQOR203RIQZ0P0Q020Q0SQJRP0Z00QZ00QUR3K

Rhomphaea prociciens female with egg sac. Photo: Jon Hart (used with permission).

My first encounter with this genus was observing Rhomphaea fictilium. Fictilis means “clay” in Latin, and the Latin-derived English adjective fictile “means capable of being molded.” The abdomens of Rhomphaea fictilium are worm-like and flexible, allowing the spider to change its shape. This ability may help Rhomphaea to camouflage itself in different contexts – the shortened abdomen of the little one in the photo above helps it to blend in with the seed heads it rests on. When their abdomens are held out long and straight, these spiders can look like very convincing sticks. The incredible photo below shows an individual that looks like it has the tail of a (very tiny) dragon!

Rhomphaea_fictilium_Gergin_Blagoev

Rhomphaea fictilium with extended abdomen (dragon’s tail?). Photo: Gergin Blagoev, licensed under CC BY 3.0.

As well as having wonderfully strange morphology, Rhomphaea have rather unusual habits. Most spiders are generalist predators, and spiders in the family Theridiidae typically build tangle webs that they use to catch crawling insects and other arthropods, including other spiders. Rhomphaea, unlike most of their relatives, specialize on hunting other spiders. They do sometimes build their own rudimentary webs from just a few silk lines, but they also enter the webs of other spiders and use aggressive mimicry to hunt their owners. Rhomphaea will pluck the web and produce vibrations that lure the resident spider out to investigate what they perceive to be prey caught in the web. The web-building hunter then becomes the hunted, tricked into the approaching the dangerous intruder. Rhomphaea fictilium have been reported to prey on other theridiids, orb-weavers (araneids), sheet-weavers (linyphiids) and others.

Rhomphaea_Al_Denelsbeck

Rhomphaea fictilium with its unfortunate prey. Note that the spider is covered with silk – theridiids comb sticky silk out of their spinnerets with their fourth legs and throw it over their victims to subdue then before biting. Photo: Al Denesdbeck (used with permission).

These tiny, cryptic spiders are rare and difficult to spot, but keep your eyes out for them in low tree branches, grasses, and bushes – or in the webs of other spiders!

References & further reading

Bradley, R. A. (2012). Common Spiders of North America. Univ of California Press.

Exline, H., & Levi, H. W. (1962). American spiders of the genus Argyrodes (Araneae, Theridiidae). Arañas americanas del género Argyrodes (Araneae, Theridiidae). Bulletin of the Museum of Comparative Zoology., 127(2), 75-202. Full text at BHL

Paquin, P., & Dupérré, N. (2001). On the distribution and phenology of Argyrodes fictilium (Araneae, Theridiidae) at its northern limit of North America. Journal of Arachnology, 29(2), 238-243. PDF

 

Spiders of Lost Lagoon

This weekend, I was lucky to spend a rare rain-free November morning in Vancouver’s famous Stanley Park with Sean McCann, who kindly provided all the photos for this post. Despite the late season and cool weather, it turned out to be a very spidrous (a term coined by Sean) day indeed! We must remember that the end of Arachtober does not necessarily mean the end of spider season, as Eric Eaton pointed out in a recent Spider Sunday post.

Our first spider-observation stop was outside the Lost Lagoon Nature House. What at first glance looked like a dirty and unremarkable garage door turned out, upon closer inspection, to be a veritable spider heaven!

IMG_3131

Here I am making notes on an impressive aggregation of spiders.

Although not quite on the massive scale of the aggregation of thousands of orbweavers inside a wastewater treatment plant that Gwen Pearson wrote about recently, I estimate that the area around this single garage door is home to several hundred spiders all living in extremely close proximity. In this case, the aggregated webs are just a couple metres away from the edge of Lost Lagoon, a freshwater habitat that produces large numbers of chironomid midges as well as larger aquatic insects. Lights attract these insects, making this the perfect hunting ground at night, when the spiders are most active.

IMG_3133

It’s hard to see individual spiders at this scale, but looking closer, they are everywhere!

Here’s a closer look  at one small area of the door (zooming in on the upper right corner of the photo above). Two large females rest in the open while a third hides away in a silken retreat next to a cluster of 3 egg sacs.

IMG_3121

Almost all the spiders in this aggregation were members of a single species, the bridge orbweaver Larinioides sclopetarius (family Araneidae). Here are some closer shots of a male and female:

IMG_3076

Male Lariniodes sclopetarius against the blue backdrop of the building.

IMG_3104

Female Lariniodes sclopetarius posing on some nearby vegetation.

We did find a few spiders other than bridge orbweavers on the building. A female L. sclopetarius and what’s most likely a juvenile Eratigena (formerly Tegenaria) appeared to be sharing the same retreat in a cement pillar.

IMG_3172

Moments before this photo was taken, these two were hunkered down close together in the pit in the cement, apparently  oblivious to one another.

Right on the other side of the same pillar, this male longjawed orbweaver Tetragnatha elongata was hanging out.

IMG_3180

It turns out that Lariniodes and Tetrgnatha are the usual suspects when it comes to communal living and megawebs. Spiders in both genera like to live near water as was the case here next to the lagoon. Lariniodes sclopetarius often build their webs on human-made structures, and especially prefer to be next to lights (Greene et al. 2010 and references therein). This preference was very evident at the Nature House – of the four identical  garage door sections of the side of the building facing the lagoon, the spiders were almost exclusively living on the only one with a light.

Although our first stop provided plenty of arachnological excitement for one day, we eventually moved on and explored the rest of the lagoon.

We found this male Pimoa altioculata and several others of the same species on webbing underneath the railing of a small footbridge.

IMG_3245

Spiders in the family Pimoidae are related to the linyphiids, and also build sheet-webs.

When Sean removed the spider from his web to try to get some better shots, he immediately went into “play dead” mode, tucking all his legs up tightly around his body for defense.

IMG_3248

Several more longjawed orbweavers were hanging out under the railings of the same bridge.

IMG_3278

Another Tetragnatha sp. These spiders are typically found near water.

We also found this beautiful example of a hammock-shaped sheet web built by a small linyphiid.

IMG_3285

In this shot you can see the silhouette of the spider at the upper left hand side of the “hammock.”

We admired the web for some minutes before noticing the resident spider, who eventually came out onto the web for the lovely shot below:

IMG_3307

You can tell from the bulbous pedipalps that this is a subadult male. I am pretty sure the species is Neriene digna.

All in all it was a wonderful day at the park. I hope your November is just as spidrous as ours has been so far here on the wet coast!

Reference:

Greene, A., Coddington, J. A., Breisch, N. L., De Roche, D. M., & Pagac, B. B. (2010). An Immense Concentration of Orb-Weaving Spiders With Communal Webbing in a Man-Made Structural Habitat (Arachnida: Araneae: Tetragnathidae, Araneidae). American Entomologist, 56(3), 146-156.

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?!
IMG_1957

After a minute or so, she went back for her abandoned prey.
IMG_1960

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.
IMG_1974

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.
IMG_2101

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.

Untitled-1

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

Long, cryptic spiders

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!

IMG_8002-2

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.

IMG_8966

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.

IMG_8964

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.

IMG_8008

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.

IMG_8020

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.

IMG_8026

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.