dungeon-monster poison death-match drama

what	when	where	pic
spider, amaurobiidae, probably genus Coras	2010-10-12, 2130 hours	basement
millipede	2010-10-12, 2130 hours	basement

I make no apologies for the title. True, there was no dungeon, but the action took place in our basement — so that’s close enough (have you seen our basement?). The characters may not have actually been monsters, but the cast did include an eight-legged eight-eyed doubled-fanged spider and a creeping millipede, so give me partial credit. Of course, there wasn’t any real poison…wait. Poison actually was involved, and there will be some elaboration on that later. And it most certainly was a death match — with a surprise twist at the end, an extra turn of the screw, so keep reading.

But first: some gratuitous philosophizing! I’ve been asked: why the interest in insects and spiders? The answer is much the same as Geoff Mallory’s comment on climbing Mt. Everest: because they’re there. We live in the suburbs of Boston. We don’t have duck-billed platypuses and we don’t have Great White Sharks facing off against orcas. But we do have a plethora of insects and spiders, all of them utterly bizarre and alien. Each species is the result of 4 billion years of evolution. Each species is the best in the world at some subset of tasks, or it would not have evolved. Each individual struggles every day to eat and mate and not be eaten. How could this not be interesting? (Plus, it became clear we were faced with a choice: either clean the house more often, or learn to appreciate the spiders.)

Anyway, as I turned on the light in our office downstairs, I noticed a spider on the floor. So I did what anyone would have done and went and got the camera. At first I thought it was a wolf spider or an Agelenid, but on further observation it seems to belongs to the order Amaurobiidae, the hackle-mesh funnel web spiders. The species is tough to distinguish, but the genus is probably Coras.

This is when another actor entered the stage. Creeping out from a crack in the wall, just a couple of centimeters away, was a millipede. It was clear things were about to get interesting, so I responded by getting flustered and forgetting how to take pictures. Here’s one after the millipede climbed all the way out — and blithely crawled towards the spider.

The spider seemed to be facing away from the crack in the wall, or I would have believed that it was actually lying in wait. Still, when it noticed the nice juicy millipede a body length away, it knew exactly what to do.

Amaurobiids, like nearly all other spiders, are predators. They’ve evolved into killing machines. They make funnel webs, like their cousins the Agelenids. But unlike Agelenids, Amaurobiids are cribellate. To make it simple, they do not trap their prey in sticky silk; instead, they create ropes of silk that are hackled, that have loose threads that can enmesh their victims.

As with nearly all other spiders (notable exception: Uloborids), Amaurobiids are venomous. Also as with nearly all other spiders, this venom isn’t really a big deal to humans. These are funnel web builders, but are not related to the Australian funnel web spiders, which are genuinely nasty, just like everything else in Australia (I’m referring to the other animals. Mostly.)

I haven’t been able to identify the millipede so far, even though it’s the standard small crawly one you always find in your house (okay, that we find in our house). Perhaps in the order Julida, perhaps Parajulida? If you can help me with this, please do so. Millipedes are detritovores, and are happy to eat pretty much any of the debris that’s found in any house. They’re slow, and one of their main modes of defense is curling up in a ball to save their sensitive underbodies. Essentially, they’re tiny little goats, except with an extra limb or a hundred.

The spider worked over the millipede pretty well in this phase. The photos are found here: http://picasaweb.google.com/gaurav1729/Wildlife20101012_spider_vs_millipede#. This particular set of photos runs from photo number 6 through photo number 81. Since I was mostly taking photos on repeat mode, you can recreate the sequence by simply clicking on the left arrow as fast as you can. (Akash later asked me why I didn’t simply make a video of the attack. I’d like to say that it was because the video camera didn’t focus that closely, but the truth is I didn’t think about it until he brought it up. Should I be alarmed my five year old has more common sense than I do?)

The spider appears to have bound the millipede with silk, and appears to be trying to envenom it with its fangs, which are at the tip of its chelicerae. It did this by moving in a circle around the millipede looking for an opening.

Note that the fangs point inwards. Agelenids, like every other spider I know of in this area, are araneomorphs, which means that their fangs swing inwards for stabbing, as opposed to mygalomorphs (such as tarantulas) whose fangs move up and down. Mygalomorphs are supposed to be more “primitive”, presumably meaning that they are more similar to the ancient spider progenitors.

Here’s a side view of those fangs:

The millipede, on its account, appears to be trying to coil up to protect its vulnerable underside. At the end, it seems to have achieved this, but is otherwise bound and vulnerable.

This is where I left for a while, to get ready for bed. The millipede wasn’t going anywhere, and it seemed a matter of time before the amaurobiid would poison it. I came back in about ten minutes to check in, and the photographs taken after that are number 82 through number 360 (!). Most of these were taken in automatic mode, so you can keep pressing the left arrow to get an animated view of what transpired.

The battle, it turned out, was far from over. The spider was running around the millipede crazily, as if had become unhinged. Left alone in the center, the millipede was writhing wildly, perhaps to try to shuck the silken fetters? The encounter at this point appeared to be some kind of bizarre Bacchanalian dance ritual. I believe that the spider was trailing silk the whole time, and each perambulation wrapped another layer around the poor millipede.

It seemed that there were several opportunities for the spider to bite, especially since the millipede was writhing around so much, exposing the underparts:

Things seemed pretty settled at this point. The millipede really looked more like a mummy of a millipede, what with all the silk draping it. But then, a surprise. Starting at photo number 306, the spider metaphorically shrugs, slides a few steps off to the side and … stands catatonic. The millipede meanwhile takes it all in stride and keeps writhing (to rub off the silk?).

It took a few minutes of these gymnastics for the millipede to feel comfortable enough to crawl off, back to the dark cave whence it came. And all that time, the spider stood stock still, close enough to grab and bite whenever it felt like — if it could.

So: what just happened? Ah. It turns out that not just spiders, but millipedes have the ability for chemical warfare, too. Which chemicals do they have in their arsenal? Let’s just say this: millipedes may be like goats, as I compared them to above, but they’re goats that have the ability to emit hydrogen cyanide. (It depends on the millipede, but HCN is a pretty popular choice in the millipede world. Other weapons include toxic liquid secretions). So score one for the prey of this world in this particular battle!

What happened to the spider? It didn’t stay there for very long after the millipede disappeared. As soon as it came out of its daze, it zipped out to the crack the millipede had vanished, and I could have sworn there was a baffled look on its face, kind of Dr. Evil when he’s just been frustrated once again.

He then sighed, shrugged his shoulders again, and crawled off to his dark lair to try his luck again.

That’s the end of this story, folks. But a few technical details. As I mentioned, at first I thought it was a wolf spider or an Agelenid, but it ended up being an Amaurobiid. Here are some of the distinguishing characteristics. First, note the fingerlike spinnerets sticking out behind:

By the way, there are several pictures that show those spinnerets pointing in opposite directions, which I had no idea they could do:

Secondly, here’s the dorsal pattern. The pattern on the abdomen itself is almost identical to Agelenids, but the pattern on the thorax is one of the suggestions that it isn’t. Also note how dark the banding on the legs is, another reason it got put in Amaurobiidae.

\

\

And lastly, here’s the eye pattern, as best as I could get it with the camera I have, in the dim internal lighting:

The relationship between Agelenidae and Amaurobiidae has been a puzzle to me ever since I learned that this particular spider was a member of Amaurobiidae, and I want to talk a bit more about why, and what issues this puzzle raises. First of all, note how close the family resemblance is: similar funnel webs, almost identical dorsal abdominal pattern, the spinnerets look similar, and the eye pattern is very close. This cannot be a coincidence, right? Even for spiders, which are notoriously difficult to distinguish, these resemblances are pretty striking. The two families must be evolutionarily closely related. But look at the distinction between them: the cribellum, the organ that strums the silk to create the hackled ropes. This is a very fundamental difference in how silk is produced, and since spiders are all about the silk, that’s a very fundamental difference between the two families. So the sequence must be thus: a common ancestor of Agelenids and Amaurobiids is either cribellate or ecribellate, and then one part of this family either loses or gains the cribellum.

So why am I confused by this? Simply because there are actually many families that are cribellate and ecribellate. By the logic described above, this distinction must have evolved multiple times. This must be a fascinating example of convergent evolution. But hold on: the different cribellate families are quite varied from each other (and also the different ecribellate ones). So why did so many quite distinct families make the same decision, to drop the cribellum, while two very similar families (Agelenidae and Amaurobiidae) decided to go different paths? I’d love to know more about the evolutionary pressures working here.

Here’s an article I found on the evolution of spider webs that discusses some of these issues.

Finally, I just wanted to say that poor Akash felt really bad about missing this, because it was after his bed time. Someone once said that he never slept early, because he felt that if anything interesting were to happen to a twenty year old young man, it would certainly happen after 2 am. Apparently, that’s true for five year olds, too.

[POSTSCRIPT:

2023-07-07 Coras is actually now in Agelenidae, not Amaurobiidae.

Previous postscript:

This posting was initially published Oct. 16th, 2010. I sent a link to it to reddit.com, expecting maybe fifty page views. I ended up with more than 300,000 views in the next 24 hours. I am in awe of the awesome might of reddit. And I will never again underestimate how weird a place the internet is. Here’s the thread on reddit.. And here’s a list of tweets about this posting.

This also led to some further information about the incident. In the original article, I called the spider an Agelenid, while at the same time distinguishing some features that seemed anomalous (such as the darker banding on the legs). Lynette Schimming of bugguide.net (my go-to website for insect identification) was nice enough to show me that the spider was not in fact from Agelenidae, but from Amaurobiidae. I’ll give myself some partial credit, in that even the venerable John Henry Comstock, in “The Spider Book”, says that Amaurobiids and Agelenids are tough to distinguish. And “The Spider Book” is the Old Testament of spider books — it brooks no yea or nay.

Also, I initially attributed a quote to Sir Edmund Hillary, that should have been attributed to George Mallory. My apologies to George Mallory — he did after all die on Everest, he shouldn’t also get deprived of credit for the greatest quote in mountaineering.

What you read above is an edited version, with some of the mistakes corrected.]