The Atavism

Sunday, June 6, 2010

Sunday Spinelesness - One for the arachnophobes?

It occurs to me that some readers might be put off by my affection for spiders. I'd be interested to see which creature, the wasp or the spider, you find yourself cheering for at the end of this post. Let's introuduce them. First, the large black hunting wasp Priocnemis monachus emerging from its burrow in one of the steps on our garden path (I messed up the focus, but nature has a way of refusing to re-pose):


And the creature the black hunting wasp has been hunting, one of the native tunnelwebs Porrhothele antipodiana:


Po. antipodiana is pretty cool spider, it's one of very few that are capable of eating snails. Snails usually avoid the attentions of ground dwelling spiders by being too slimy to get a hold off and being able to retract into their shell. Po. antipodiana get's around those defenses by hooking its fangs into the snail's body and holding on while the snail struggles, produces tonnes of mucus and finally succumbs to the spider. A couple of months ago I gave a talk to a local school who wanted someone to help their study of invertebrate lifestyles and one of the kids told me that he'd seen a tunnelweb eating a snail. The budding naturalist didn't seem at all proud when I told him that he'd observed a behaviour that was only recognised by scientist 30 years ago. I guess 30 years seems an impossibly long time when your 10!

If this particular spider looks a bit bedraggled it's because it has already been anesthetised by the wasp. Pr. monachus is a member of the family Pompilidae which, like the ichneumonidae that featured here last week, use the living bodies of other arthropods as incubators to grow their young. While most of the ichneumonidae use caterpillars to grow their larvae the pompilids specialise in spiders (which has earned them the name spider wasps). There are ten described species of spider wasp in New Zealand, each targeting a range of spider species. Pr. monachus the largest of our spider wasps, and by choosing Po. antipodiana to provision her nest this one has taken on of New Zealand's largest spiders:


Pr. monachus follows the typical pompilid nesting behavior, which means they go hunting before they set up their nest. As I watched these two the wasp would drag the spider a few centimetres then drop it and scurry back up the step and into its nest for a few seconds before returning to the spider, checking it was still incapacitated (and giving it another sting if it showed a fight) and repositioning it again. I don't know how much of that behavior was down to the wasp setting up its nest and how much was the wasp struggling with having bitten off more than it could drag up the sheer surface of the step it built its nest in.


The wasp was definitely seemed to be having a hard time hefting the spider up the step. I spent about half an hour watching her grab and the spiders legs, its spinnerets or its even its head while clinging to the sheer face of the concrete step. In the end, it started raining and I decided I should probably do something else with the rest of my weekend so I left her to her work. I came back about an hour later and both spider and wasp were gone. I don't know if the wasp gave up; or if it achieved its Herculean task and the spider's body is, even now, nourishing the next generation of these impressive wasps.


Labels: , , , , , , , , , ,

Posted by David Winter 8:29 AM


Bah! Where's your commitment to Science?? Now we'll never know!!!

Post a Comment