A comb-tailed spider

Last weekend, I joined a group of fellow arachnophiles for a day at Burns Bog. We did not achieve our goal of finding the rare ground spider Gnaphosa snohomish (a bog specialist), but instead we met a very common spider that is nonetheless not well known: a comb-tailed spider in the family Hahniidae.

Neoantistea magna, a common yet mysterious forest-dweller (photo Sean McCann).

A distinguishing feature of spiders in the subfamily Haniinae is the arrangement of the spinnerets in a single row like the teeth of a comb – thus the common name.

The arrangement of the spinnerets of ‘comb-tailed’ spiders in the subfamily Hahniinae.         (Photo by Tom Murray, licensed under CC BY-ND-NC 1.0)

I generally think of spiders as being one of two basic types: wanderers or web builders. The wanderers include visually hunting ground dwellers like wolf spiders, whereas web building spiders are sit-and-wait predators that rarely leave their silken snares. This is overly simplistic, of course, but asking “web or not?” is often a useful first step in  classifying spiders. The genus Neoantistea, however, gave me a first encounter with members of an intermediate group known as vagrant web builders.

The sheet webs of Neoantistea spiders are tiny – typically less than 5 cm across. They are built in moss or across shallow depressions such as those formed by the tracks left by animals walking on soft ground. The diminutive spiders (their total body length is less than 5 mm) live under their webs, retreating into crevices in the litter or moss when disturbed.

Small sheet-web of Neoantistea magna (photo Sean McCann).

What makes these spiders unusual for web builders is that although the web can be a useful aid for catching prey, it is not necessary. Neoantistea magna have reasonably large eyes and can recognize and hunt prey just as easily off of their webs as on them (Engers & Bultman 2006).

A portrait of a male Neoantistea magna, showing the arrangement of the relatively large eyes (photo Sean McCann).

Although it was easy to identify the spiders we found to genus – the distinctive spinnerets leave no doubt as to the family, and of the North American members of the Hahniinae, Neoantistea is the only genus of web builders – determining the species was another matter entirely. Usually spider identification relies on close examination of the genitalia.

To ID this handsome fellow, two of the key features were the tibial apophysis and the patellar spur, tiny protrusions of the pedipalps which are very difficult to see without a microscope (here’s a diagram of the segments of the pedipalps).

The key to identifying spiders often lies in the features of their elaborate genitalia. Here the large curved outgrowth on the tibia and the hooked spur on the patella of the pedipalp are circled (photo Sean McCann).

Speaking of genitalia, although very little is known about the biology of Neoantistea magna, there is one report of mating behaviour (Gardner & Bultman 2006). During copulation, the male clasps the female with his first two pairs of legs. The robust femur and tibia (see leg segment diagram) on each of these legs are studded with a double row of tubercles, giving them a serrated look. 

Male N. magna. Note the burly front legs, presumably modified for grasping the female (photo Sean McCann).

Although the female may attempt to disengage from her partner, he is able to maintain a firm hold with his rather spectacularly modified legs and continue copulation.

Female N. magna, with slender front legs (photo Sean McCann).

Fun with etymology:                                                                                                             The genus name Neoantistea means “new Antistea”. Antistea comes from the Latin word antistes, which means “one who stands in front of a temple, overseer, high priest”. Why were these tiny spiders given such a grandiose name? It’s a mystery.

References

Engers, W., & Bultman, T. (2006). Foraging Habits of Neoantistea magna (Araneae: Hahniidae).

Gardner, D., & Bultman, T. (2006). Natural History and Reproductive Biology of a Hahniid Spider in Southwestern Michigan.

Opell, B. D., & Beatty, J. A. (1976). Nearctic Hahniidae (Arachnida: Araneae). Bull Mus Comp Zool Harvard Univ.

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.

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!

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!

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.

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.

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)!

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.

 A Sitticus male?

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

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).

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

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!

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.

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

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: 1–30.

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: 1153–1155. doi: 10.1126/science.182.4117.1153

Spiders of Mount Tolmie

Spring is springing in Victoria, and it’s a great time to see spiders. Sean insisted that I take a break from the intense data-wrangling I was working on yesterday afternoon to take a walk at Mount Tolmie. We were rewarded with an amazing abundance and diversity of spiders, just by flipping over a few rocks. Here is a selection of our most exciting finds, by family.

(All photos by Sean McCann)

Salticidae 
Our adventure began with another observation of spider-on-spider predation. This lovely reddish jumping spider’s victim is unknown – perhaps a sac spider (family Clubionidae).

Pimoidae
Pimoa altioculata. Pimoidae is a family of spiders that is closely related to the Linyphiidae, and one I have never before encountered. The name Pimoa comes from the Gosiute language, and means ‘big legs’. An rather apt description for this leggy spider, found hanging out near a couple of egg sacs.

Lycosidae
Alopecosa – named for a fox. We found several of these gravid (pregnant) wolf spiders under the stones.

This one was hiding out in a burrow.

Gnaphosidae
A ground spider with its characteristic cylindrical spinnerets visible. 

Theridiidae
The western black widow, Latrodectus hesperus, can usually be found under the rocks at Mount Tolmie. They are not nearly as abundant there as at Island View Beach, however.

Corinnidae
The prize of the day was Phrurotimpus borealis. Phrurotimpus means ‘guarder of stones’, in reference to their habit of dwelling under rocks. These tiny spiders are ant-mimics, with the first pair of legs held forward like antennae (ants are also abundant under the rocks at Mount Tolmie). This one is a mature male.

Dictynidae or Cybaeidae (?)
Finally, a mystery spider that we initially mistook for an amaurobiid.

Not shown, but also encountered, were many Tegenaria (some of which are now Eratigena) (Agelenidae) and a pair of Dysdera crocata (Dysderidae). At least nine families is not too shabby for an impromptu afternoon stroll!

Many thanks to Robb Bennett for his kind help with identification.

Phidippus and Salticus

Two spiders, both alike in family,

Phidippus johnsoni, the red-backed jumping spider. (Photo: Sean McCann)

Salticus scenicus, the zebra jumper. (Photo: Sean McCann)

In fair Victoria, where we lay our scene,

Uplands park, Victoria, BC, is among the many homes of these common jumping spiders (family Salticidae). (Photo: Colin McCann)

From ancient grudge break to new animosity,

Where spider blood makes spider fangs unclean.

Notes
Jumping spiders (like all spiders) are generally predators of insects and other arthropods. Spiders are the second most common prey items of Phidippus johnsoni (27% of their diet, just after dipterans, coming in at 30% of the total count), and comprise 5% of the diet of Salticus scenicus.

References:
Jackson, R. R. 1977. Prey of the jumping spider Phidippus johnsoni (Araneae: Salticidae). J. Arachnol. 5 :145-149.
Okuyama, T. 2007. Prey of two species of jumping spiders in the field. Appl. Entomol. Zool. 42 (4): 663–668.

The zebra jumper’s stripes may serve as camouflage in many settings, but in this case they were no match for the excellent visual hunting abilities of a fellow salticid. (Photo: Sean McCann)

 

Oxyopidae: sharp, cat-like spiders

The family Oxyopidae contains 448 species of spiders in 9 genera. They have a worldwide distribution but are (like so many groups) most speciose in the tropics. I had never encountered one personally before traveling in Central and South America, but it turns out we have two species in the genus Oxyopes in Canada!

Oxyopids (also known as lynx spiders) all have 8 eyes, and can be easily distinguished from spiders in other families by their characteristic hexagonal eye arrangement, as well as the often dagger-like spines (called macrosetae) on their legs. The family name Oxyopidae is derived from the genus name Oxyopes, which is a combination of the Greek word for ‘sharp’ (ὀξύς), and the Latin word for ‘foot’ (pes). Sharp-legged is a rather apt description for many members of this family. (Update: according to Spiders of North America it means sharp-eyed, which is also an accurate, but slightly less obvious, descriptor.)

A female Oxyopes salticus (one of the two lynx spider species found in Canada) sporting impressive (sharp-looking!) spines on her legs and the characteristic hexagonal oxyopid eye arrangement. Photo by Thomas Shahan, licensed under CC BY-NC-ND 2.0.

Members of this family are generally diurnal hunters, with keen eyesight (for spiders) and great agility. Like the cats they are named after, lynx spiders often stalk and pounce on their prey. They are proficient jumpers, and some might even be mistaken for a salticid at first glance. This one (click the link, it’s worth it!) looks like it might actually mimic a jumping spider. 

This cryptic oxyopid (a Hamataliwa species) we found in Honduras fooled me twice: at first glance it looked like a bump on a twig, and on my second look, after realizing it was a spider, the size and posture had me thinking it was a salticid. Photo: Sean McCann

Some oxyopids are ambush predators, staking out flowers and waiting for unsuspecting insect visitors. Like crab spiders (Thomisidae) with similar behaviour, green lynx spiders have the ability to slowly change colour (the process takes several days) to match the background they are sitting on – usually flowers.

A green lynx spider (Peucetia viridans) from Fort Pierce, Florida. This species can change its colour to match the background it sits on (see some examples of better background-matching here under ‘identification’). Photo: Sean McCann

Like the disparate forms these spiders take – compare the Peucetia viridans above with the Hamataliwa grisea below – they also have fascinating variety in their habits. 

A Hamataliwa grisea found in Gainesville Florida. Photo: Sean McCann

While most lynx spiders are cursorial hunters that don’t use silk for prey capture, there is one web-building genus (Tapinillus), including a social spider species that engages in communal web building and cooperative prey-capture!

Peucetia tranquillini is a wanderer that invades the orb-webs of female Nephila clavipes, locating and preying on courting males by responding to their vibrations, and sometimes vibrating the web themselves, apparently to attract a resident spider (a possible example of aggressive mimicry). One individual was also found residing in the tangle-web of a brown widow (Latrodectus geometricus) for several days, capturing prey caught in the web, and even stealing prey captured by the web owner (kleptoparasitism).

Spiders in the genera Oxyopes and Peucetia are members of what I like to call the centimetres high club: they mate in the air, hanging from a silken thread spun by the female. In one species, the male wraps the female in a silk ‘bridal veil‘ before copulation.

Oxyopes scalaris, the other lynx spider that can be found in Canada. Photo by Kyron Basu, licensed under CC BY-ND-NC 1.0.

Mother green lynx spiders guard their egg sacs and newly emerged spiderlings, and will fiercely defend them by spitting venom. While the spitting spiders (Scytodidae) shoot a deadly combination of venom and silk out of their fangs to capture prey, this seems to be the only spider with venom-spraying defensive behaviour.

A gravid female green lynx spider (Peucetita viridans), capable of forcibly ejecting irritating venom from her fangs. Photo: Sean McCann

Check out the following posts for even more information about awesome oxyopids:

• Erin McKiernan on green lynx spiders.
• Bug Eric on striped lynx spiders.
• The green lynx as a featured creature, from the University of Florida.

What happens when you poke, prod and pinch black widow spiders? You might be surprised…

This post originally appeared on Chris Buddle’s blog Expiscor at Scilogs.com.

A stunning female western black widow (Photo: S. McCann)

People seem to have a particular fear mixed with fascination when it comes to venomous animals, and whenever I talk about my work with black widows I am invariably asked questions like, “have you been bitten yet?” The answer is, of course, no. Spiders almost never bite people. I’m always quick to relate that in my experience black widows are not aggressive, even when I go around poking and prodding them with my bare hands.

Replicated experimental results always carry more weight than anecdotes, however, so I am delighted to share this recent paper: Poke but don’t pinch: risk assessment and venom metering in the western black widow spider, Latrodectus hesperus.

Hey look!! An actual peer-reviewed research paper about the poking, prodding, and pinching of black widows, confirming that they are reluctant to bite, even when threatened. Not only that, but the study provides some cool data suggesting that these spiders are capable of assessing risks to make decisions about how to defend themselves.

Here are the details:

David Nelson and his coauthors wanted to know if black widows change their defensive behaviour depending on the level of threat they are faced with. To find out, they used gelatin ‘fingers’ to place spiders in three different threatening situations: a ‘low threat’ attack was a single poke with one finger, a ‘medium threat’ was a series of prods simulating a more persistent attacker, and the ‘high threat’ was three a series of long pinches of the spider’s entire body between two fingers, as might be experienced if being grasped by a predator.

Figure 1 from Nelson et al. 2014

They found that the spiders engaged in several distinct defensive behaviours during these experimental attacks: retracting the legs toward the body, moving (often retreating), ‘silk-flicking’ (drawing sticky silk out of the spinnerets with last pair of legs and flinging it toward the attacking finger), ‘playing dead’ (curling up into a ball), and biting.

During low-threat, single pokes, no bites occurred. Most spiders were completely non-confrontational, simply moving away, and only rarely flicking silk.  When the threat level escalated to persistent prodding, the spiders changed their defensive behaviour: roughly half of them flicked silk, some played dead, and only one spider (out of 43) attempted to bite the offending finger. Silk-flicking is much safer than biting for a black widow – she can maintain her distance while flinging sticky silk to subdue or slow down her attacker. Biting, on the other hand, requires getting up close and personal with the assailant in order to pierce it with her tiny fangs, making her much more vulnerable to injury.

See the red tips of this black widow’s puny fangs? It’s a lot safer for her to keep her distance in threatening situations than get close enough to use them (Photo: S. McCann)

Only when the spiders were being pinched between two fingers (with the mouthparts already positioned right up against their ‘attackers’) did biting start to become a more common, last-resort tactic: 60% of the spiders bit the fingers as a result of being squeezed for an extended period of time, delivering on average 2.7 bites each. Pinching also resulted in silk-flicking by about half of the spiders, and a few played dead.

This is all great information, but when the spiders did bite the gelatin fingers, there was no way of knowing how much venom they injected, if any at all (sometimes venomous animals deliver ‘dry’ bites). The next question the researchers wanted to answer was, do the spiders control whether and how much venom they inject when biting? In particular, they wanted to know if the amount of venom injected would vary depending on the type of threat (in this case either pinching a leg with forceps, or grasping the abdomen with gloved fingers).

For this experiment they came up with a clever method to collect the venom: a small vial with a thin membrane over the opening was presented as a target for the spiders to bite. If a spider did bite, her fangs would pierce the membrane (the number of holes would indicate how many times) and any venom she expelled would be collected in the vial so the volume could subsequently be measured.

It turned out that more than half of all bites were dry (no venom was detected in the vials). The black widows delivered more bites per target when they were pinched on a leg than on the abdomen, but more venom was released with each bite when the abdomen was pinched. Being grasped by the body is a high-risk situation for a black widow because her abdomen is unarmored and vulnerable; a strong squeeze or puncture can be deadly. Pinching a single leg, on the other hand, represents a non-life threatening attack. Spiders can autotomize (drop) their limbs and survive without significant ill effects.

The team also found evidence that the spiders delivered more venom per bite when repeated threats were spaced 5 minutes apart than 5 seconds apart. Attacks after the longer intervals might have been interpreted as coming from new assailants, each requiring a larger dose of venom than a second or third bite to the same persistent attacker.

The results all indicate that black widows have fine control over how much venom they inject when biting. First, they can decide whether or not to use venom at all. Some spiders gave dry bites, then wet bites, as well as vice versa, demonstrating that dry bites were not simply a result of running out of venom. Furthermore, they can vary the amount of venom they inject during individual bites and in response to different kinds of threats.

Both silk and venom are metabolically expensive to manufacture, so it makes sense that spiders would be selective about when and how much of these resources to deploy in defense. This study suggests that they are able to assess risks and adjust their responses accordingly, only dipping into their reserves of silk and venom as the threat level escalates towards a life-or-death situation.

What does this all mean for humans? Grabbing and pinching spiders is generally not a good idea – they might get injured and could bite defensively. This is just good sense and didn’t require a scientific study to confirm, but the new data suggest that even if a black widow does bite, she’s not necessarily going to inject any venom. It’s also important to note that in the experiments where bites did occur, the spiders always had a ‘finger’ or target placed in direct contact with their mouthparts.

An unaggressive female black widow takes a stroll across my hand. Although I never grab spiders to pick them up, coaxing them onto my hands and letting them wander around on their own steam has never been a problem. (Photo: S. McCann)

The most exciting thing this study tells us is that spiders can make decisions about how to respond to threats (which sometimes include humans) – further evidence of their incredible sophistication. Perhaps more importantly for the arachnophobic, it suggests that black widows would much rather conserve their valuable venom for use in dispatching their next meal than waste it on a human who is of no interest as prey!

Spiders in general are amazing creatures worthy of our admiration and respect. I hope that this new information about black widows might convince some that there is more about them to be fascinated by than to fear!

References and related reading:

Nelsen, D. R., Kelln, W., & Hayes, W. K. (2014). Poke but don’t pinch: risk assessment and venom metering in the western black widow spider, Latrodectus hesperus. Animal Behaviour, 89, 107-114. http://dx.doi.org/10.1016/j.anbehav.2013.12.019

Vetter, R. S. (1980). Defensive behavior of the black widow spider Latrodectus hesperus (Araneae: Theridiidae). Behavioral Ecology and Sociobiology, 7(3), 187-193. doi:10.1007/BF00299363

W. Cranshaw (2014). Western widow fact sheet: http://www.ext.colostate.edu/pubs/insect/05605.html

Hasta luego, Honduras!

Tomorrow Sean and I will land back home in Canada (to take a strategic break from fieldwork in Honduras). While it’s unfortunate that our current trip is being cut short, the future looks bright. When we return in a couple of months, not only will we continue our study of Red-throated Caracaras, it looks like we will also be participating in some serious arachnology! No doubt lots of cool discoveries are waiting to be made, and we will continue to blog about both projects. Already during our time in Honduras we’ve found plenty of awesome spiders that will be featured in future posts. For now, please enjoy these lovely jumping spiders (all photos by Sean McCann)!

Kids and Spiders in Honduras

Here in Honduras, Sean and I have happily taken the opportunity to interact with some great local kids who seem almost as excited about spiders as we are!

We lent them some plastic tubes for collecting, and they headed off to search for cool spiders around town. In no time at all, they brought back an impressive collection, from tiny jumping spiders to massive wandering spiders.

These kids are totally fearless, casually picking up spiders that are about half the length of their hands! Sometimes they were a bit too enthusiastic in their efforts to capture a speedy specimen, and one brought back a partly crushed spider and a bite on his finger to show for his efforts. (Spiders do occasionally bite, but only as a last resort if they are in a life-threatening situation!) He seemed more proud than upset by this result, but we tried our best to encourage gentler handling from then on!

Here’s a selection of the best shots from one afternoon of collecting (all photos by Sean McCann).

A large wandering spider (family Ctenidae). I’m not sure about the identification, but she looks similar to the Ancylometes bogotensis I wrote about in a post on ‘bridal veils‘.

A lovely female grey wall jumper, Menemerus bivittatus. This species can also be found in the southern U.S.

A male grey wall jumper (I’m guessing he was caught in close proximity to the female), doing what wall jumpers do, hanging out on a wall.

A tiny tarantula spiderling! Notice that the back end of the abdomen is bald… most likely in response to a kid trying to capture it, this spider has shed its defensive urticating hairs (more about tarantula defenses here).