The Atavism

Sunday, February 28, 2010

Sunday Spinelessness - Arachnophobia

If you read The Atavism regularily you may have gathered I'm quite fond of spiders (1, 2). So, by and large I'm with the Bug Chicks when if comes to arachnophobia. -No spiders will go out of there way to attack people and there's only a handful of species with toxin that packs any punch to humans so, rationally, there is really nothing to worry about. In keeping with that policy, when this handsome Cambridgea male turned up in our bathroom I saw it as a photo opportunity.

cam1

Then he ran cross my camera, up my arm and lodged himself at home on my neck. All my affection for spiders and rationality with regards to the risks lasted about a tenth of a second. I didn't actually scream but it's fair to say my heart rate was somewhat elevated and my movements were restricted. But why? What is is about spiders that freaks us out so much? I did a bit of digging through the academic databases but psychology really isn't my science and I couldn't get a clear idea. Researchers in Germany* have shown (at least among German undergraduate students) spiders do have a special place in our fears - people are more likely to respond badly to photos of spiders than other arthropods, even hymenopterans which can prose a more serious threat to people than spiders. But the question of why remains. Evolutionary psychologists have suggested arachnophobia might be an adaptation but it's hard to imagine that selective pressure applied by occasional spider bites would be sufficient to drive a specific fear of them. Perhaps lots of spiny legs, beady eyes and fearsome fangs just set off enough triggers in the brain to elicit a unique response (did I mention psychology's not my science...).

I remember reading a more plausible (and even testable) idea about the origin of arachnophobia in one of Steven Pinker's books that didn't pop up in my search of the literature. I don't have the book in front of me (and I can't even remember which one it was, although it sounds like a Blank Slate kind of an idea) so you might want to take this with even more grains of salt than you usually would with adaptationist ideas. From memory the argument went that we may be born with a general fear of all spiders and snakes but, until recently, would have learnt the few that are actually dangerous in the area we grew up in from our families. With the good guys and the bad guys separated we could stop wasting our energies on being worried by the overwhelming majority of species which are benign. An inbuilt arachnophobia with inbuilt malleability to surroundings. In the West we aren't exposed to many spiders of any sort in our youth so we retain the childish arachnophobia all our lives. It's a nice story whether it's true or not doesn't seem to have been tested.

Oh, and if my photo of a Cambridgea didn't put you off Te Ara has a much scarier one.


*Spiders are special: fear and disgust evoked by pictures of arthropods. Antje B.M. Gerdes, Gabriele Uhl, Georg W. Alpers. Evolution and Human Behavior, DOI: 10.1016/j.evolhumbehav.2008.08.005)

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Posted by David Winter 7:13 AM | comments(2)| Permalink |

Sunday, January 31, 2010

Sunday Spinelessness - Motherly Devotion

I promised last week that I'd come up with something a bit more cheery than photos of dead flies for the next Sunday Spinelessness post and what could be more uplifting than portraits of motherly devotion? Of course, in this case the mother is a spider. The New Zealand lynx spider Oxyopes gracilipes.

Gravid Lynx Spider

Lynx spiders are a family (Oxopidae) of very active and fast running hunting spiders. The swollen abdomen of the female photographed above is evidence of her gravidity (I was tempted to dedicate this post to Harvest Bird who finds herself in the same condition but I'm not quite sure how someone a little less arachnophilic than I would take that). A few days before I spotted the gravid female I'd taken some pretty poor photos of a male lynx spider on the same plant so we can probably assume he's the father.

LynxM

And because that photo really is pretty awful here's another male lynx spider I found crawling around on our house

lyncM2

That's a bit more like it. In this one you can see a few of the defining morphological characteristics of the lynx spiders - spiny legs, a hexagonal arrangement of eyes very large and palps in males. O. gracilipes also displays a few behavioral traits that are typical of lynx spiders, it's active during the day there is a great deal of maternal investment in offspring. Here's our female again, a little over a week after the first photo.

lynxF2

She's lost her former globose shape because she's laid her eggs. The silk she's spun around the leave is protective egg sag but lynx spiders take protection very seriously - they won't leave the fate of their eggs to a bit of silk and chance. I checked on the egg sac almost every day for two weeks and never found the lynx spider more than a few centimeters away. Little is known about the behaviour of our lynx spider but their American counterparts have been known to relocate egg sacs when they are threatened by predators or starve to death while standing guard. In the end I had to leave before the spiderlings hatched but in Spiders of New Zealand and their Worldwide Kin Ray and Lyn Forster tell us that the female wanders off shortly before that event.

As ever you can click on the images to get to a higher resolution version.

lynxF3

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Posted by David Winter 9:14 AM | comments(2)| Permalink |