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)
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!
Our main goal is to find lots of these! (Photo: Sean McCann)
But I am looking forward to seeing lots of these too! (Photo: Sean McCann)
This post is not about spiders (sorry for any disappointment this may cause). Instead, it’s about some amazing (crazy?) neotropical raptors that specialize in preying on the brood of social wasps!
Red-throated Caracaras (Ibycter americanus) in French Guiana. These birds are members of the family Falconidae, and they are specialist predators of social wasps. (photo: Sean McCann)
Getting close enough to a wasp nest to eat its contents is no mean feat–as anyone who has ever been stung by a worker wasp defending its nest can probably attest. I was privileged to be involved in a study of these birds in French Guiana, led by Sean McCann.
Today, Sean and I and all our co-authors got a belated Christmas present with the publication of our paper in PLOS ONE.
Here’s a quick video summary of our research, narrated by me and Sean:
For more information, videos, and photographs, head over to Sean’s blog, Ibycter.
UPDATE (28 July, 2018): The scientific names used in this post are out of date. The giant house spider is now Eratigena duellica, and the hobo spider is Eratigena agrestis. Tegenaria domestica remains the same!
Living in Vancouver, I frequently hear about a HUGE hairy spider that was trapped in the bath or lurking in the bedroom or scuttling across the kitchen floor. More often than not, it’s described as a wolf spider (family Lycosidae). I’m pretty confident that every single time, the spider being referred to is actually a member of the family Agelenidae, and in particular, the genus Tegenaria. I’m almost as certain that the species in question isTegenaria duellica, commonly called the giant house spider or European house spider.
NOT a wolf spider. Female Tegenaria duellica (Agelenidae) Photo: Sean McCann*
Sometimes the slightly better informed giant-spider-spotter will have taken a closer look at the spider, or photographed it, then done some online research and concluded that it’s the ‘dangerous’ hobo spider, Tegenaria agrestis.
Female hobo spider, Tegenaria agrestis. These spiders may also be found in houses on the west coast of BC, but are generally not as large as T. duellica.
There is a lot of flat-out wrong information on the internet about hobo spiders and their supposed ability to cause necrotic lesions. Some people mistakenly refer to T. agrestis as aggressive house spiders. (1) They aren’t. And, (2) agrestis means ‘of the field’. As for ‘dangerous’, arachnologists Robb Bennett and Rick Vetter
“know of no authentic Canadian report of hobo spider envenomation.”
See their paper on the misdiagnosis of spider bites in Canada for more reasons not to fear hobo spiders. Having done a bit of work with Tegenaria agrestis, both in the field (on Vancouver Island) and in the lab, I can personally confirm that they are far more likely to be running away from humans than attempting to bite them (just like other Tegenaria species).
A charming female Tegenaria. Neither aggressive nor at all interested in human flesh.
Both hobo spiders and giant house spiders can be found living alongside humans on the west coast. They are not easy to tell apart, but Rick Vetter and Art Antonelli have prepared an excellent identification guide that will tell you at the very least if it’s NOT a hobo spider (not that there would be any cause for alarm if it was one). In a house in southern BC, that leaves you with T. duellica (larger) or T. domestica (smaller).
If it has long pointy palps like this guy, it’s NOT a hobo spider, but either T. duellica or T. domestica.
Even without the (fairly recent) hype about the ‘medically significant’ hobo spider, humans seem to generally fear and despise Tegenaria. In The World of Spiders—a delightful bookin which the author’s passion for his subjects fairly leaps off every page–W.S. Bristowe admitted that he had no affection for house spiders. In their defence, however, he wrote that,
“A Tegenaria cannot deliver a painful bite. Its unpopularity arises from its leg span, its rapid movements and general creepyness.”
Male Tegenaria duellica. Long-legged and disposed to ‘general creepyness’.
The movement of these spiders is indeed disconcerting. Males are pretty much all leg, and they can run FAST. Bristowe noted that Tegenaria atrica can run a distance equivalent to 330 times her body length in 10 seconds. This means a human-length (let’s say 5’9″, or 1.75 m) Tegenaria could run the 100-metre dash in 1.73 seconds. Pretty speedy.
But apart from their occasionally-startling dashing to-and-fro (mainly in the fall when males go on the prowl, abandoning their webs to search for females), house spiders in general are fabulous to have around. They are great at taking care of all manner of arthropod home-invaders and are really fun to observe.
House spiders, like this Tegenaria that set up shop just inside the door of our lab, help out by snacking on any bugs that might also enjoy living inside buildings.
If you really can’t stand having them in your home, relocate them outside, and with luck they’ll find a nearby crevice in which to build the retreat of their funnel-shaped webs. You probably won’t often catch them out on their silk sheets, as they will run and hide in their retreats at the slightest disturbance.
Usually house spiders wait for prey just inside their tube-like silk retreat. We enjoy attempting to entice this Tegenaria (who lives just outside our lab) to come out and say hi by dropping small insects onto her sheet web. The speed with which she can dart out and snag prey is quite stunning!
If you’re still not convinced that house spiders are good neighbours rather than enemies, you could always try Bristowe’s method for curing fear of Tegenaria: eat one**.
*Sean McCann, a house spider enthusiast, provided all the photographs for this post. He’d like it to be noted that in addition to being incredibly fast, house spiders also *sound* creepy (if you’re lying on the floor and one runs past your head).
**It didn’t actually end up curing his fear of house spiders, but he did win a lot of money as a result.
Mating behaviour and silk use in (some) mygalomorphs
So in my ‘intro to spider systematics’ post, I wrote that most of the Mygalomorphae are tarantulas. This is not actually true when you consider total numbers of species. Of the 2775 mygalomorph species (in 16 families), 950 species are in the family Theraphosidae (tarantulas), so that’s actually only about 34%. I probably should have said that the tarantulas are the most common mygalomorphs (and the ones people are generally most familiar with). Theraphosidae definitely wins the prize for the largest mygalomorph family, though. The next most speciose family is Nemesiidae, with 364 species.
I also implied that the Mygalomorphae aren’t all that sophisticated when it comes to silk use. Whereas the Araneomorphae have the ability to spin several different kinds silk specialized for particular functions, the Mygalomorphae produce only one general purpose silk. This is not to say, however, that they have not come up with some marvellous silk-based innovations!
In the centre of the vegetation in the foreground, you may spy the mouth of a well camouflaged silk-lined ‘turret’ built by a mygalomorph in the family Antrodiaetidae. (Photo by M. Hedin, licensed under CC BY 2.0)
Mygalomorphs have poor vision, so they must rely on chemical (smell or taste), vibratory, and tactile senses. It was traditionally thought that these relatively ‘primitive’ spiders had simple sexual communication systems. However, in their recent review in the Journal of Arachnology, Ferretti and coauthors argue that the sexual behaviour of mygalomorphs actually involves some quite elaborate courtship displays and complex mechanisms of communication. This post will highlight the 6 mygalomorph families described in the paper, most of which use silk in various ways for both prey capture and sexual communication.
Now, as a general rule, spiders are predatory, and mygalomorphs are no exception. They’re pretty keen to snap up anything that blunders into their field of vibratory perception, even if it’s another spider. The main functions of courtship behaviour in mygalomoprhs are mate recognition, orientation and synchronization of sexual behaviour, and suppression of non-sexual responses. Females must advertise their location and receptivity, and males must somehow signal “male, not meal!” to their potential partner. This can be tricky when the stage on which the male must show off his desirability as a mate is the same one that the female uses to detect prey. We’ll see what kinds of things these spiders get up to in order to make it to the finish!
Antrodiaetidae: turret mygalomorphs
Antrodiaetidslive underground in silk-lined burrows. The burrow entrance is extended with a turret made from silk, soil, and plant material that blends in beautifully with the surrounding substrate. The spider waits for prey just out of sight inside the tube, where she can detect and quickly respond to vibrations produced by insects brushing against the litter encasing the turret. Males detect the female’s location using pheromones – chemicals acting as olfactory personal ads – on the silk that lines her home.
Antrodiaetus riversi (Antrodiaetidae) in feeding position in turret (Photo by M. Hedin, licensed under CC BY 2.0)
Dipluridae: funnel-web mygalomorphs
The diplurid funnel-web is a horizontal silk sheet leading to a tubular retreat in a crevice or perhaps under a stone or log. From this silken hideout, the spider detects vibrations produced by prey passing over her sheet web. The female’s funnel-web also forms the dance-floor for the male’s vibratory courtship display. The male’s courtship signals are transmitted to the female through the silk sheet. Typically, she does not respond, which is great news for the male! Presumably his pedipalp drumming and many legged tap-dancing is quite distinct from prey vibrations, inhibiting the predatory tendencies of the female.
Ischnothele caudata (Dipluridae) female in her funnel web. Note the elongated spinnerets characteristic of this family. (Photo by M. Hedin, licensed under CC BY 2.0)
Mecicobothridae: sheet-web mygalomorphs
Mecicobothriidae is a family containing nine species of small spiders that build sheet-webs on the soil. In Mecicobothrium thorelli, chemical and/or tactile signals on the female’s silk trigger the male’s courtship display. Like in the diplurids, the male’s dance moves transmit vibrations through the silk to the female, who sits passively in judgment. The receptive female apparently enters a cataleptic state, allowing the male to haul her around the web and manoeuvre her into just the right position. It’s not quite as easy as all that for the male, though. In order for a successful copulation to occur, the chelicerae of the spiders must interlock in a very specific way. If the couple is disturbed while in copula, or there are any difficulties disengaging from this toothy embrace, it’s game over for the male, and dinner time for the female. Once the deed is done, a successful male will stick around on the female’s web, attacking any other males attempting to try their luck with the female. This ‘mate guarding’ behaviour is very unusual among mygalomorphs.
FemaleMecicobothrium thorelli(Mechicobothriidae) on her sheet-web. (Photo credit: Gabriel Pompozzi)
Theraphosidae: tarantulas
Theraphosids often live in silk-lined underground burrows, or silken retreats under rocks and vegetation. Sometimes they even build their tube-like homes in trees. Pheromones on the silk allow males to find and recognize females, and also trigger courtship behaviour. Males transmit species-specific vibratory courtship signals through the ground, to the female listening in her burrow. These seismic love songs can be detected by females at a distance of more than one metre. In Avicularia avicularia, the female actively responds, tapping her first pair of legs and pedipalps on the substrate. These good vibrations tell the male she is receptive to his advances, and may also help the male orient toward her.
Immature Avicularia avicularia (pinktoe tarantula) (Photo credit: Sean McCann)
Nemesiidae: tube-trapdoor mygalomorphs
Nemesiids generally live in silk-lined burrows, sometimes finished with hinged, camouflaged trap-doors. Male courtship includes scratching and tapping with the legs on the ground, often at a distance from the female’s burrow entrance, suggesting that this is another form of long-distance seismic communication. While most female mygalomorphs remain relatively passive throughout courthship and copulation, Acanthogonatus centralis females jerk violently, twitching all their legs and pedipalps. This enthusiastic behaviour may stimulate the male to begin copulation.
Calisoga longitarsis (Nemesiidae) at burrow entrance (Photo by M. Hedin, licensed under CC BY 2.0)
Microstigmatidae
The family Microstigmatidae contains 16 species of tiny spiders (males are only 1-3 mm long!). This is one family that apparently makes minimal use of silk. Xenonemesia platensis males only begin courtship after making direct contact with the female’s body. The male’s courtship behaviour includes quivering with the first two pairs of legs. The female, if she is receptive, responds by moving into a mating posture with her genital area exposed, allowing the male to clasp her pedipalps and chelicerae with his first legs.
This clasping of the female’s chelicerae by the male is common in mygalomorphs; in many species males have specialized structures on their legs that facilitate the embrace. Some researchers think it may be a way of restraining a potentially lethal female, keeping her fangs at leg’s reach. However, the fact that female catalepsy during copulation is also widespread sheds some doubt on this interpretation. Alternatively, it may be a more ‘symbolic’ form of bondage akin to the bridal veil in some araneomorphs. The tactile stimulation associated with the male’s clasping may in fact cause the female to become quiescent.
Throughout copulation, the Xenonemesia platensis male continues his tactile courtship, tapping and scraping his second pair of legs against the female. It’s possible that this copulatory courtship persuades the female to use his sperm over that of competitors, but more work needs to be done to test this hypothesis.
Mating Xenonemesia platensis (Microstigmatidae). The male has the female’s pedipalps and chelicerae clasped in his first pair of legs, while he uses his second pair of legs to beat and scrape the female’s coxae (leg segments closest to the body) (Photo credit: Gabriel Pompozzi)
The mygalomorphs may all look fairly similar, but they have surprisingly diverse habits, and use their multi-purpose silk in clever ways. Their sexual communication is most certainly not simple, incorporating multiple signaling modalities. Just as with most araneomorphs, good vibrations and sexy scents are the key!
Growing evidence suggests that contact sex pheromones associated with female silk are common in mygalomorphs (as they are in araneomorphs). Sex pheromones have also been implicated in the sexual communication systems of some spiders in the Mesothelae, suggesting that chemical communication was acquired early in the evolutionary history of spiders.
This story of mygalomorph mating also highlights the fact that female spiders in general are not simply passively waiting for marauding males to stumble across their doorsteps. On the contrary, they actively advertise for a mate, sometimes participating in a vibratory signaling ‘conversation’ with courting males, and likely judge a suitor’s quality both before and during copulation.
The private lives of spiders never cease to fascinate!
Special thanks to Gabriel Pompozzi for allowing me to use his photographs of Xenonemesia platensis and Mecicobothrium thorelli. Check out more of his fantastic images of mygalomorphs here.
I am also very grateful to Marshal Hedin for generously making his photographs available under creative commons licenses. He has some really wonderful sets of shots of several mygalomorph families on flickr.
I participated in a ‘thesis bootcamp’ last week, which basically means I was locked in the library all day (food was brought in!) writing and attending workshops. This was great for getting lots of *serious* thesis writing done, which really needs to be happening right now, but means I haven’t had much time to write blog posts. Instead, for today, I’ve gleaned a selection of great spidery blog posts from all the awesome arachnophiles who tweeted spider and web-related stuff for #SpiderMonday last week. Enjoy!
@docdez posted spider highlights from the journal of the Entomological Society of BC. Be sure to click the links to the JESBC covers for beautiful drawings of spiders by Robb Bennett and Wayne Madison!
A very patient and creative person used red thread to repair damaged spider webs!
Finally, try your hand at identifying which of these photos by @Myrmecos are of spider silk (I got it quite wrong), then check out the answers with full, uncropped images
Following from last week’s story about silk bridal veils, this post focuses on another rare use of silk in spider courtship behaviour: the giving of silk-wrapped ‘nuptial gifts’.
This phenomenon has been most well studied in two spider species in closely related families: Pisaura mirabilis (Pisauridae)
Pisaura mirabilis male carrying a silk-wrapped nuptial gift. (Photo by Ferran Turmo Gort, licensed under CC BY 2.0)
These spiders can teach us three valuable lessons about gift-giving in advance of the holiday season*.
1. Gift-giving can improve mating success.
In both families, nuptial gift giving behaviour is essentially the same. Before mating, the male obtains a prey item, (usually) wraps it up with silk, and offers it to the female during his courtship display. If she’s in the mood, she’ll grasp the package in her chelicerae, and while she’s busy consuming the prey inside, the male will copulate. It’s possible to mate without providing a gift, but in both Pisaura mirabilis and Paratrechalea ornata, males that give gifts have higher mating success: they have longer copulation durations and fertilize more of the female’s eggs.
2. Failure to wrap delicious gifts may result in their consumption, but no sex.
Females willingly accept unwrapped prey items, but may run off with them before mating can occur. This happens much less frequently with wrapped gifts, which are easier to hang on to. In Pisaura mirabilis, if the female tries to abscond with a gift that he still has in his grasp, the male goes limp (called thanatosis, or death-feigning) and allows himself to be dragged along with the gift. Once the female settles down to eat it, the male springs back into action and copulates.
3. Attractive silk gift-wrap will effectively disguise useless items, but only for a limited time.
Visual appeal may play some role in whether females accept nuptial gifts, but in Paratrechalea ornata, there are chemical cues specific to the male’s gift-wrapping silk that elicit female grasping behaviour. One of the advantages of this is that males can get away with giving females worthless items such as seeds, plant material, or prey that they’ve already fed on. Provided it’s wrapped up in attractively scented (or tasty) silk, the female will accept the gift and the male can copulate. As soon as the female realizes there’s no food inside the package, however, she’ll cut the mating short.
So there we have it. Pick the perfect prey item, wrap it up in silk, and hang on tight!
*Lessons may have limited application to non-spider interactions
For a lot of people, black widows inspire fear, but to me they are friends with amazing habits and shy, unaggressive* natures. Check out Chris Buddle’s post over on Expiscor for a conversation about these beautiful, misunderstood spiders!
Sean handles a juvenile western black widow. No, he did not get bitten! (photo: Sean McCann)
*In my experience, black widows are not aggressive towards humans. With potential prey (various arthropods including other spiders), of course, it’s an entirely different story!
Hot on the heels of Black FlyDay, today we can celebrate Spider Monday!
In honour of this web-tastic day, I would like to showcase the most awesome spider I have ever personally met: a member of the family Hersiliidae (tree trunk spiders). The beautiful photos that follow were all taken by Sean McCann, in French Guiana.
Um… is there supposed to be a spider in this photograph?
The special thing about this spider is her incredible camouflage!
Here’s a closer look:
Aha! There she is. And what’s that she’s guarding so closely?
Not only does the spider’s body blend into the background, but you might not even have noticed that she’s guarding an egg sac. What I find most remarkable is that she has evidently decorated her silken egg sac with lichen and bits of plants to make it blend in with the rest of the tree trunk.
An even closer view. Check out those elongated spinnerets! The hersiliids are also sometimes referred to as two-tailed spiders.
I didn’t even notice the extremely elongated spinnerets characteristic of the Hersiliidae until I looked closely at the photographs, so perfect is the camouflage on all the spider’s appendages. It’s probably because they are so cunningly cryptic that there seems to be very little known about the biology of hersiliids.
For more great photographs and the story of how I met my favourite spider, check out Sean’s blog post here.
I’m currently sifting through mountains of literature on spider biology searching for references to silk use in courtship and sexual communication.One of the particular topics I’m interested in is the rarely reported ‘bridal veil’. So far I’ve found records of bridal veils in 12 families, all in the Araneomorphae. I’ve included photos of most of the species in question (or a species in the same genus) to highlight the morphological diversity of the spiders that share this weird and wonderful behaviour!
Safe sex
Courting a female can be a risky business. Spiders are predators (with some exceptions), and sometimes highly aggressive females would rather treat a male as dinner than a date. Male spiders have diverse, complex repertoires of courtship behaviours, some of which most likely function to inhibit the predatory tendencies of females.
The paired pedipalps of male spiders are modified for transferring sperm. This means that, usually, the male needs to copulate twice in order to secure paternity of as many offspring as possible. The mechanics of copulation are often complex, and the male can’t afford any untimely interruptions. Possibly, the bridal veil has a role to play…
Getting tied down
Bristowe coined the term ‘bridal veil’ in his 1958 paper describing the mating behaviour of the crab spider Xysticus cristatus and Xysticus krakatuensis (Thomisidae).
Xysticus cristatus female (photo credit: Arlo Pelegrin)
Part of the male’s courtship behaviour includes anchoring the female’s legs and cephalothorax (front body segment) to the substrate with a ‘veil’ of silk threads. After mating, the female apparently has no trouble freeing herself from her silken bonds.
The centimetres high club
The nursery web spider Pisaurina mira (Pisauridae) puts a spin on the bridal veil idea.
In this species, courtship and mating take place as the spiders hang in midair, suspended by their draglines below a leaf. Before copulation, the male ties up the female’s first two pairs of legs in front of her cephalothorax, by spinning silk as he twirls the female around on her thread. Bruce and Carico (1988) suggested that the split-second that it took for the potentially cannibalistic female to struggle free from the veil gave the male just enough time to climb up out of harm’s way.
Oxyopes schenkeli (Oxiopidae)males have very similar bridal veiling behaviour, which results in the binding of the female’s first three pairs of legs with silk.
The context of courtship in these spiders is also up in the air, suspended by silk draglines from a leaf (60-90 cm above the ground). After observing at least one male getting cannibalised despite spinning a bridal veil, Preston-Mafham 1999proposed that the main function of the bridal veil is to stimulate the female to mate, possibly via pheromones (chemical signaling molecules) on the silk.
A touch of silk
The courtship of Dictyna volucripes (Dictynidae), takes place on the female’s web.
The male begins by depositing silk on the web, at a distance from the female, before approaching and applying a light silk wrapping to her body. Starr (1988) concluded that males of this species are not in any real danger from females – although females occasionally rushed towards males, males were able to easily avoid them.
Meta segmentata is a long-jawed orb-weaver(Tetragnathidae).
The veiling behaviour in this species was described as “partial wrapping of the female as though she were prey”. Lopez (1986)suggested that the silk of the bridal veil might inhibit female aggression through physical contact with sensory hairs on her body.
Throughout copulation, Schizocosa malitiosa (Lycosidae)males release dragline silk over the upper surface of the female’s front legs.
Penultimate (one molt away from maturity) Schizocosa male (photo by Marshall Hedin, licensed under CC BY 2.0)
A fairly sparse bridal veil is a common element of courtship in the genus Latrodectus (Theridiidae).Since I study western black widows (L. hesperus), I’ve included a video of one of ‘my guys’ doing his thing (video taken by Samantha Vibert)
Ross and Smith (1979), studying L. hesperus, and Aisenberg et al.(2008), studying S. malitiosa,suggested that the bridal veil silk is impregnated with a pheromone that induces female catalepsy. Placing the pheromone-laden silk directly on the female’s body might be the best way to ensure that she receives the chemical message and remains passive throughout copulation.
Homalonychus theolougus penultimate male (photo by Marshall Hedin, licensed under CC BY 2.0)
These are wandering spiders, and mating takes place on the ground. With the female’s legs all drawn up close to her cephalothorax, the male circles around her, binding her legs together tightly with a ring of silk. After the first copulation, he’ll add some more silk, reinforcing the ring, then mate a second time. As soon as the second copulation is completed, the male beats a hasty retreat. A second later the female breaks free from the silk ring, and spends some time grooming, trying to remove all the silk from her legs.
Thalassius spinosissimus (Pisauridae) females build a special mating web and hang from it in ‘mating posture’ with all the legs drawn in tightly as described above for the homalonychids. Males in this species also ring the female’s legs with silk (Sierwald 1988).
The male starts by spinning an ‘outer’ ring of silk around the female’s tibiae, then he adds a second, ‘inner’ ring around the patellae (see diagram with names of leg segments here). His handiwork complete, he tips the trussed-up female over onto her side and mates with her (Merrett 1988).
Cupiennius coccineus (Ctenidae)males, in staged encounters with heterospecific (Cupiennius salei) females, sometimes engaged in bridal veil spinning behaviour.
Here’s where it starts to get interesting. Normally, when mating with females from their own species, Cupiennius males don’t go in for the bridal veil thing. However, when researchers paired C. coccineus males with C. salei females (who are on average a bit bigger than the C. coccineus females), some males circled the female, depositing silk on her legs. Two of the three males that spun bridal veils were able to mate with the heterospecific females, while the third became lunch. As Schmitt (1992) noted in reference to this unfortunate male’s demise, “Obviously, the male silk did not seriously affect the female’s mobility.”
One explanation is that the ‘veil’ in this situation is a result of some confusion over whether to treat the too-large female as a potential mate, or prey (these guys can take down prey larger than themselves and normally use silk in this context). Another option is that this is a part of the courtship repertoire of Cupiennius males, but it’s reserved for especially large, potentially dangerous, females and was never seen before because usually similarly sized individuals were paired for laboratory mating observations (Schmitt 1992).
Courtship in both Argiope aemula (Araneidae),
Argiope aemula female (photo by falilin, licensed under CC BY 2.0)
and Nephila pilipes (Nephilidae),
Nephila pilipes female (photo by drriss, licensed under CC BY 2.0)
takes place on the female’s orb-web. The tiny male does a variation on the ring-type bridal veil, doing his silk spinning on the top of the female’s cephalothorax and abdomen (he’s so small he has room to walk around on there). He attaches silk at the bases of the female’s legs, building up a complex network of silk (Robinson and Robinson1980).
Lifting the veil
Recently, Zhang et al. (2011) published the first experimental study of the function of a bridal veil. The authors wanted to figure out if the bridal veil in Nephila pilipes has any role in reducing female aggressiveness, and if so, whether chemical and/or tactile cues were responsible.
In the lab, males never spun bridal veils prior to their first copulation. When female movement interrupted the first copulation, males that deposited silk inevitably copulated a second time, while most males that tried to mate again without spinning a bridal veil were cannibalized.
The researchers then compared the success of normal, silk-slinging males with males that had their spinnerets covered with super-glue*. It turned out that these males did just as well as normal males by going through the motions of bridal veiling behaviour even though they were prevented from spinning silk. Further experiments preventing females from detecting potential chemical and/or tactile cues associated with bridal veil spinning behaviour suggested that both touch and smell are likely involved.
Tying it up
Are bridal veils physical restraints or stimulating strands? Is silk a substrate for sexy scents or catalepsy-inducing compounds? It’s really not clear. Given that female spiders commonly produce silk-bound pheromones, I suspect that male silk pheromones are probably important. However, it’s becoming increasingly apparent that spider communication systems are highly sophisticated, and messages may be simultaneously transmitted between individuals via multiple modalities. Spiders use vibratory, chemical, tactile, and (sometimes) visual signals and senses in a variety of combinations, and untangling this mystery will take a lot more investigation!
*In case you’re concerned that super-gluing spiders is not a nice thing to do, I can assure you that cyanoacrylate is recommended for use on spiders in the book Invertebrate Medicine. I’ve looked into it because I’ve done some spider gluing myself.
References without direct links in the text:
Bristowe, W.S. 1958. The World of Spiders. Collins, London.
Lopez, A. 1986. Glandular aspects of sexual biology. In: Ecophysiology of Spiders (Nentwig, N., ed.). Springer Verlag, Berlin, pp. 121—131.
Merrett, P. 1988. Notes on the biology of the neotropical pisaurid, Ancylometes bogotensis (Keyserling) (Araneae: Pisauridae). Bulletin of the British Arachnological Society. 7: 197-201.
Preston-Mafham, K.G. 1999. Notes on bridal veil construction in Oxyopes schenkeli Lessert, 1927 (Araneae: Oxyopidae) in Uganda. Bulletin of the British Arachnological Society. 11(4): 150-152
Schmitt, A. 1992. Conjectures on the origins and functions of a bridal veil spun by the males of Cupiennius coccineus(Araneae, Ctenidae). Journal of Arachnology 20:67–68.
All the information that follows is from Rainer Foelix’s excellent book Biology of Spiders. Photos used with permission from Sean McCann.
Here I will provide a brief orientation to the spiders that I hope will help place future posts that feature spiders in different suborders, orders and families. I will try to add more detailed taxonomy information as I go along. Also, I hope this post will help me to remember some basic information that I am always re-learning (never again will I look up orthognath vs. labidognath!).
There are about 40,000 more than 44,000 identified species of spiders in 110 112 families* (I hope that someday I will have posts highlighting every family!).
The order Araneae includes all the spiders. There are three suborders:
The most ‘primitive’ (phylogenetically oldest) spiders are in the suborder Mesothelae. They have segmented abdomens like other arthropods, and unlike the rest of the spiders. There is only one family in the Mesothelae, the Liphistiidae. I don’t really know anything else about them at this point (I will come back to them in the future).
The rest of the spiders are in the Opisthothelae, which contains the two other suborders, the Mygalomorphae and the Araneomorphae.
Both the Mesothelae and the mygalomorphs have orthognath chelicerae. Spider chelicerae are a large pair of mouthparts tipped with articulated fangs through which venom is injected into prey. Orthognath chelicerae work in parallel. Make ‘air quotes’ with your first two fingers – like that.
The majority of species in the Mygalomorphae are tarantulas, in the family Theraphosidae (in French, a tarantula is called a ‘mygale’, which makes this easy to remember ever since I spent some time in French Guiana).
There are several other less well-known families in the Mygalomorphae that I will get to in later posts. Mygalomorphs can produce silk, but most don’t build webs; they lack the pyrifrom silk glands that that araneomorphs use to cement their silk threads together or to a substrate.
Araneomorphs have labidognath (opposing) chelicerae. Touch your thumb and forefinger together repeatedly in pincer-like fashion, so. The Aranaeomorphae includes all the ‘usual’ non-tarantula spiders you might run into, including families such as the
Araneae (orb-web spiders),
A common European Garden Spider, Araneus diadematus (Araneidae), on her orb-web.
Salticidae (jumping spiders),
A gorgeous Salticid. Check out those brightly coloured labidognath chelicerae! The red bits are the opposing articulating fangs.
Thomisidae (crab spiders),
A goldenrod crab spider, Misumena vatia (Thomisidae) doing her thing.
Lycosidae (wolf spiders),
A female Lycosid carrying her spiderlings on her abdomen. Some spiders have highly developed brood care!
Pholcidae (cellar spiders),
A female cellar spider, Pholcus phalangiodes (Pholcidae) carrying her egg sac. I grew up calling these spiders daddy long legs, but that name is also sometimes used to refer to harvestmen (order Opiliones), which are non-spider arachnids.
Theridiidae (the combfooted spiders, also known as cobweb or tangle-web weavers),
Female western black widow, Latrodectus hesperus (Theridiidae), on her tangle-web.
Agelenidae (funnel-web weavers),
Female hobo spider, Tegenaria agrestis (Agelenidae). Her close relatives T. domestica and T. duellica are often found in homes.
and lots of other less common/well-known ones that I intend to make posts about in due time. Although some of them don’t build webs at all, they all produce silk draglines that can be anchored to a substrate (often useful as a sort of ‘safety line’).
To sum up, the relationships and basic differences between the three suborders look like this:
For more about the phylogenetic relationships among the Araneae see the tree of life page.
UPDATE: I learned this morning that the in the latest phylogenies Opisthothelae is considered a suborder, with Mygalomorphae and Araneomorphae as infraorders.
*UPDATE 2: Thanks to Chris Buddle for pointing me to the latest information at the World Spider Catalog!
