Sunday, March 29, 2009

The Hunting Modes of a Wolf Spider

Taking a break from stalking prey amid the jungle of leaf litter in my front yard, this spider sprinted across my patio last Monday night. I managed to drop my compass next to him (the edge of which has a two inch ruler) and approximate his Cephalothorax-to-spinneret length at about 7/8 of an inch.

My best guess is Lycosa gulosa, though I’m somewhat doubtful due to the size of this beast… (If anyone else has an alternative ID be sure to let me know.)

Wolf Spiders are ferocious predators, and in captivity have been shown to scavenge as well as hunt. They hunt mostly by cruising; moving slowly and deliberately through high prey areas, taking precaution as to not raise the notice of local cockroaches, moths and other quarry. They also occasionally practice an ambush mode of hunting during which they remain motionless – or even actively conceal themselves – waiting for unwary meals to stumble on them.

The cruising and ambush styles of hunting have evolved specifically as counters to the sensory systems of prey species – to either avoid detection while on approach, or, to completely overwhelm the capabilities of the prey’s sense organs. As detailed in a recent article by Jérôme Casas, Thomas Steinmann and Olivier Dangles, “crickets, cockroaches and other orthropteroid insects are equipped with air-flow sensors (filiform hairs) at the rear end of their abdomen. They possess many short hairs, serving as acceleration sensors, and fewer long hairs (velocity sensors) on their cerci. These mechanosensors are among the most sensitive sensors in the animal kingdom, with action potentials triggered by less than one tenth the energy of a photon; indeed, the orthropteroid escape system, and in particular fluid flow sensing using filiform hairs, has maintained textbook-example status over many years. Thus, we hypothesised that spiders use the two different hunting strategies to cope with optimal air-flow detection by crickets.”

If you have an interest in spiders, or arthropods at all, check out The Aerodynamic Signature of Running Spiders to see the results of using Digital particle image velocity (DPIV) measurements of a running spider in an air tunnel to estimate prey response…

Casas, J., Steinmann, T., & Dangles, O. (2008). The Aerodynamic Signature of Running Spiders PLoS ONE, 3 (5) DOI: 10.1371/journal.pone.0002116


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