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.

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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 dont 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.

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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.

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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 hesperusAnimal Behaviour89, 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 Sociobiology7(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)!

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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.

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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).

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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‘.

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

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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.

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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).

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A comparison of the vibrations transmitted by courting males and ensnared prey in two web-building spider species.

Today, I am excited to publish my first blog post about some of my own spider research! Our paper, “A meal or a male: the ‘whispers’ of black widow males do not trigger a predatory response in females”, has just been published in Frontiers in Zoology (freely available online).

This study is part of the PhD work of my friend and collaborator Samantha Vibert. In fact, we did some of the data collection and analysis for this paper during my very first semester in our lab, when I was working as an undergraduate research assistant. That was when I first began to really look closely at spiders and their incredible behaviour. My experience working with Sam that summer sparked my passion for the complexity and beauty of all of the various aspects of the private lives of spiders, which so often go unnoticed by humans.

Here is a plain-language summary of the paper, written with Samantha Vibert, and with photos by Sean McCann:

Spiders are fascinating but largely overlooked creatures, with sophisticated signalling systems involving chemical, vibratory, tactile, and in some species visual communication. A spider’s web is essentially an extension of her exquisitely tuned sensory system, allowing her to quickly detect and respond to vibrations produced by entangled prey. Not only is the web a highly effective prey-capture device, but it is also the dance floor on which prospective mates must demonstrate their desirability. The first moments after a male spider steps onto a female’s web may present a great risk, since spiders are often cannibalistic. We were interested in how a dancing male spider avoids a potentially deadly case of mistaken identity. One way that he might deal with this challenge is by transmitting vibratory signals that are very different from the vibrations produced by ensnared prey.

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Spider webs are highly effective prey-capture devices, so how does a courting male avoid the fate of flies like this one?

Our study species were the western black widow and the hobo spider, which are both found in British Columbia.

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A western black widow (Latrodectus hesperus) hanging from her tangle-web under a log at Island View Beach on Vancouver Island.

Black widows are in the family Theridiidae, and build complex, three-dimensional tangle-webs, while hobo spiders (family Agelenidae) build dense sheet-webs. Female black widows are much larger than males, while hobo spider males and females are closer in size.

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A hobo spider (Tegenaria agrestis) female on her sheet web at Iona Beach, in Richmond, BC.

The purpose of our study was to describe some of the vibratory courtship signals of males in these two species, and to determine which aspects of these vibrations might allow females to discriminate between prospective mates and their next meals.

First, we recorded the vibrations transmitted through the web by courting males in both species using a laser Doppler vibrometer. At the same time, we video-recorded the male’s courtship behaviour. This allowed us to describe and analyze the different kinds of vibrations that were transmitted through the web during specific behavioural elements of each male’s courtship display. We then recorded the vibrations produced by the struggles of two types of common prey insects (house flies and crickets), on both black widow and hobo spider webs.

We found that male and prey vibrations differed more in the black widow than in the hobo spider. Hobo spider male vibrations contrasted with prey vibrations only in terms of their duration – the courting male moves around almost continuously on the female’s sheet web, while prey struggles are generally brief and intermittent. Black widow male courtship vibrations were also longer than prey vibrations on tangle webs (for the same reason), but they were also distinctive based on their generally lower amplitude and higher dominant frequencies.

To our surprise, we also found that most courtship behaviours in both species did not generate the kind of very stereotyped, complex and distinctive “songs” that have been reported in several other spider species. These species tend to court on substrates like leaf litter and plants, which most likely transmit vibrations quite differently than webs. Some male orb-weavers also produce highly rhythmic patterns during their vibratory courtship displays. So our finding leads us to wonder to what extent web architecture and complexity might constrain the transmission of the male courtship signals, and therefore the design of these signals.

One very interesting exception to the rule turned out to be the vibrations generated by the male black widow’s abdomen tremulations (an up-and down waggle of the abdomen, performed as the male hangs upside down from the female’s web). These vibrations were always very distinct from anything produced by prey: they were long-lasting and of very low amplitude, like a constant humming.

Here’s a short video of a male western black widow vibrating his abdomen on a female’s web (Supplemental File 1 from Vibert et. al 2014):

To learn more about these particularly stereotyped, ‘whisper-like’ male signals, we built our own custom web vibrator by modifying a loudspeaker. We were then able to play recorded vibrations of a male’s abdomen tremulation or a fly’s struggles back to females and observe their responses. Black widow females were much less likely to respond aggressively to vibrations played back at the “whisper-like” low amplitude of male abdomen tremulation, but attacked when we turned up the volume to levels typical of prey vibrations. This was the case regardless of which type of vibration we played. So we speculate that the males vibrate their abdomens either to avoid triggering a female’s predatory response, or even to turn it off.

Is it possible that the females that didn’t attack low-amplitude vibrations simply couldn’t detect them? We don’t think so. First, spiders are specialists when it comes to detecting even faint vibrations, and second, some females actually responded with courtship behaviour: abdomen ‘twitches’ which are similar to the male’s abdominal movements, but more emphatic. These abdomen twitches undoubtedly transmit their own vibrations through the web, and it would be very exciting to further investigate the female’s side of the vibratory ‘conversation’ during courtship.

Abdomen vibration seems to be a relatively common type of courtship behaviour and has been described in several spider families (‘abdomen wagging’ in an orb-weaver, and what has recently been described as ‘twerking’ in jumping spiders are a couple of examples). If indeed the “whispers” caused by these vibrations are involved in lowering female aggression, this might explain why such behaviour is fairly common among spiders.

The orb-weaver Argiope keyserlingi’s courthip also involves abdomen vibration, but in this species another vibratory signal was recently implicated in reducing the risk of cannibalism. The ‘shuddering’ of a courting male delays the female’s predatory response. One of the common features of black widow abdomen tremulation and these ‘shudders’ is that they are the first courtship behaviour performed by males after they enter a female’s web.

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A male western black widow courting a large, potentially dangerous female. Abdomen vibration is performed on and off throughout the male’s courtship display, starting just after the male steps onto the web, and featuring prominently during attempts to approach and mount the female.

Very little is known about the kinds of vibratory courtship signals that male web-building spiders transmit to females through their webs, except for in orb-web weaving species. We hope that this new information about vibratory communication in tangle-web and sheet-web building spiders will contribute to better overall understanding of the function and evolution of web-borne vibratory courtship signals.

References:

Vibert, S., Scott, C., and Gries, G. (2014). A meal or a male: the ‘whispers’ of black widow males do not trigger a predatory response in females. Frontiers in Zoology, 11(4).  doi:10.1186/1742-9994-11-4

Wignall, A. E., & Herberstein, M. E. (2013). The Influence of Vibratory Courtship on Female Mating Behaviour in Orb-Web Spiders (Argiope keyserlingi, Karsch 1878). PloS one8(1), e53057. doi:10.1371/journal.pone.0053057

Wignall, A. E., & Herberstein, M. E. (2013). Male courtship vibrations delay predatory behaviour in female spiders. Scientific reports3doi:10.1038/srep03557

The spiders in and around our apartment in Gualaco

Our first field expedition is scheduled for next Monday, and we still have a lot of preparations to make, including a trip back to Tegucigalpa to submit some official paperwork and buy additional equipment. While we’ve been settling in and getting things organized here in Gualaco, we haven’t gone out much, except for a visit to our new friend Rafael’s farm. That’s not to say we haven’t had a chance to find more spiders though!

On the walls (inside and out) of our new apartamento alone, we’ve found two lovely jumping spiders (Salticidae),

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and a very handsome wandering spider (Ctenidae) with neat spikes on his abdomen.

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We were somewhat less enthused to spot several of these other arachnids on one of our outside walls…

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A questing tick (family Ixodidae)! We would definitely prefer not to become a host for any of these arachnids.

Just outside is a yard full of plants, rocks, mud, and debris, which is variously occupied by the horses, pigs, dogs and other animals that wander freely through the town. This explains the abundance of ticks, and from now on we’ll be careful of wandering through this area!

At night, under the light of a headlamp, the yard sparkles with the eyes of many spiders. The other evening, a very brief investigation yielded the discovery of several wolf spiders.

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A mother wolf spider carrying her spiderlings (called pulli-carrying behaviour). Almost all female lycosids carry their offspring on their abdomens, with some exceptions.

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A male lycosid that looks like the same species as the female above.

If anyone knows more about the identities of these spiders, please let me know in the comments!

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

Hola from Honduras!

We finally made it to our destination, the town of Gualaco in the department of Olancho, after three long days of travel (including an unexpected detour through San Pedro Sula due to poor weather preventing our plane from landing in Tegucigalpa). After spending two nights in a local hotel, we’re now installed in an affordable apartment (the rent is about a tenth of the cost of similar accomodation back home in Vancouver) that will serve as our home base for the coming months.

Things are definitely different here – for one thing, there is no hot running water in Gualaco.  This is the slightly scary, and mostly ineffective, electric showerhead that was in our hotel room. We are not sure yet whether we’ll invest in one for our new home.

Yesterday, we took a trip up some very interesting roads to the pine forest where we’ll start our caracara work. We visited the site where a local named Isidro (who will be our guide for the next month) monitored a red-throated caracara nest last year.

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We had a very long and interesting ride, with eight people in one 4-wheel drive pickup, along some extremely bumpy and muddy roads. We passed this unfortunate boa constrictor, which evidently chose the wrong time to cross the road.

Although we didn’t have much time to stop and investigate or photograph cool animals as we hiked in and out from the nest site, Sean did manage to snap a couple of shots of spiders that we passed by.

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A wolf spider (family Lycosidae) with her silk-wrapped egg sac attached to her spinnerets.

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An Argiope (Araneidae) with a beautiful star-shaped stabilimentum.

We also have plenty of familiar spider friends in our apartment, that appear to be helping with the moth infestation.

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Lucky for us, our apartment contains an abundance of cellar spiders (Pholcidae)! Here’s a female with her egg sac clasped in her chelicerae, and an attending male.

Once we’ve had more time to explore local habitats, I am sure I will be able to post lots more about the spiders of Honduras! Hasta luego!

Thanks to Sean for all the photos.

Heading to Honduras

It’s been quiet here for the last couple of weeks because I’ve been busy wrapping up loose ends in the lab, visiting family, putting all my worldly possessions into storage, and packing, in preparation for a big field trip. Today, Sean and I will travel to Honduras (via Dallas, Houston, and Miami) to study Red-throated Caracaras (awesome raptors that are specialist predators of social wasps) in an area where they are threatened. We will do extensive surveying and hopefully radio-tracking of the birds to get some basic data to inform conservation efforts. Sean will be blogging about our efforts at ibycter.com.

This is what all the gear we’ll need for 3 months of field work looks like. (Photo: Sean McCann)

Believe it or not, all that stuff fit into our 4 bags!

Somehow, all that stuff fits into these 4 bags! (Photo: Sean McCann)

This work is the continuation of Sean’s PhD, and although it’s not spider-related, I couldn’t pass up the opportunity to go along and assist with field work in such an exotic location. While we’re in the field, I’ll be working on writing up my thesis on sexual communication in black widows. Of course, as we explore the department of Olancho in search of Caracaras, we will also be keeping an eye out for cool spiders (and other arthropods)! If it’s anything like our last field expedition to French Guiana, we’ll find no shortage of amazing creatures to observe and photograph. I hope to blog regularly about all the wonders Honduras has in store for us, so stay tuned for updates from the field!

Red-throated Caracaras (Ibycter americanus)

Our main goal is to find lots of these! (Photo: Sean McCann)

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But I am looking forward to seeing lots of these too! (Photo: Sean McCann)