Red-throated Caracaras: awesome birds that eat wasps

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)

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.

The real house spiders of Vancouver

(and other West Coast cities)

UPDATE: The scientific names used in this post are out of date. The giant house spider is now Eratigena atrica, 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 is Tegenaria 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).

duellica?

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).

male T duellica palps

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 Spidersa delightful book in 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

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.

outside

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.

Meet the Mygalomorphae!

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!

turret M Hedin http://www.flickr.com/photos/23660854@N07/4485414016/sizes/z/in/photolist-7QmVjq-hBLdXo-7L4ijK-7L8h9G-bsNAPc-bsNArZ-bsNBLK/

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

Antrodiaetids live 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.

Female Mecicobothrium 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.

Nemesiidae (M Hedin)

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!

References, resources, and acknowledgements:

For a wonderful read about the evolution of spiders and their silk, including lots more information that I didn’t include about the fascinating habits of mygalomorphs, I highly recommend Leslie Brunetta and Catherine Craig’s book Spider silk: Evolution and 400 Million Years of Spinning, Waiting, Snagging, and Mating (an excellent gift idea!).

Ferretti, N., Pompozzi, G., Copperi, S., Gonzalez, A., & Pérez-Miles, F. (2013). Sexual behaviour of mygalomorph spiders: when simplicity becomes complex; an update of the last 21 years. Journal of Arachnology, 16(3), 85–93.

Ferretti, N., Pompozzi, G., Copperi, S., Pérez-miles, F., González, A., & Pe, F. (2012). Copulatory behavior of Microstigmatidae (Araneae: Mygalomorphae): a study with Xenonemesia platensis from Argentina. Journal of Arachnology, 40(2), 252–255.

Costa, F. G., & Perez-Miles, F. (1998). Behavior, life cycle, and webs of Mecicobothrium thorelli (Araneae, Mygalomorphae, Mecicobothridae)Journal of Arachnology26, 317–329.

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.

Spider Bytes from #SpiderMonday

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!

@LeslieBrunetta posted a collection of lovely images of spider webs from Norway

Some wonderful photographs of the amazing green lynx spider by @emckiernan13

@ibycter highlighted some of the exotic spiders we have in North America. Here’s one of them:

Sitticus fasciger (photo credit: Sean McCann)

Sitticus fasciger (photo credit: Sean McCann)

Two great posts by @AndyBugGuy: tiger beetles for lunch and an incredible many-faced spider

Beautiful photos of araneus marmoreus with information on spider gentalia and mating from @tcmacrae

The usual Monday linkfest at Expiscor by @CMBuddle was exclusively spider related stuff

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

Silk-wrapped prey items are a girl’s best friend

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)

and Paratrechalea ornata (Trechaleidae).

Male of genus Paratrechalea. (Photo by Gonzalo G. Useta, 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

REFERENCES (also linked in the text)

Albo, María J., & Costa, F. G. (2010). Nuptial gift-giving behaviour and male mating effort in the Neotropical spider Paratrechalea ornata (Trechaleidae). Animal Behaviour, 79(5), 1031–1036. doi:10.1016/j.anbehav.2010.01.018

Albo, Maria J, Winther, G., Tuni, C., Toft, S., & Bilde, T. (2011). Worthless donations: male deception and female counter play in a nuptial gift-giving spider. BMC evolutionary biology, 11(1), 329. doi:10.1186/1471-2148-11-329

Andersen, T., Bollerup, K., Toft, S., & Bilde, T. (2008). Why Do Males of the Spider Pisaura mirabilis Wrap Their Nuptial Gifts in Silk: Female Preference or Male Control? Ethology, 114(8), 775–781. doi:10.1111/j.1439-0310.2008.01529.x

Brum, P. E. D., Costa-Schmidt, L. E., & de Araujo, A. M. (2011). It is a matter of taste: chemical signals mediate nuptial gift acceptance in a neotropical spider. Behavioral Ecology, 23(2), 442–447. doi:10.1093/beheco/arr209

Getting friendly with widow spiders

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 black widow in the field (photo: Sean McCann)

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!

Spider Monday: featuring my favourite spider

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?

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:

treetrunk_spider

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.

treetrunk_real_close

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.