Sunday, August 9, 2009

Spider wasp in action

Along with Rick Gardner and Ray Showman, I had one of the best botanical field trips of the year today. Mind you, this was not a trip for the faint of heart, in part because sedges - oh no! sedges and tigers and bears, oh my! - were a primary target. But both Rick and I are died in the wool caricophiles (sedge nuts), and Rick had discovered a veritable Eden for those of our ilk.

So off we went, on what must have been the hottest day of the summer to date. And the place that we went, in Gallia County in SE Ohio, was just about as far off the track as one can get in the Buckeye State. We parked on a seldom-traveled gravel country lane, and hoofed about a mile and a half back into serious floodplain swamp country, traversing several steep ridges in the process.

It was worth it, and I'll put up some of the spectacular plants that we saw later. But, as always there were other distractions, and in keeping with yesterday's theme of terrifying killers of the insect world, I want to share a very cool experience that we bore witness to, from start to finish.

As we were passing along the side of a steep ridge, I noticed one of the big showy spider wasps working an area of downed branches and accumulated leaf litter. I pointed it out to Rick, and commented that it was actively hunting wolf spiders. We stopped to watch for a bit, when the wasp suddenly dove into some leaves, and in what seemed like a few seconds, tossed out a large wolf spider, having apparently stung the victim in the blink of an eye. In no time flat the wasp had drug the already dopey spider several feet from the site of the initial encounter.


The video above was made immediately after the wasp scored the spider.

I believe this wasp is Entypus unifasciatus, one of the larger and showier of the parasitoid wasps. They are comspicuous, as they continually flick their wings and spread their antennae, both of which are boldly marked with yellow. Just speculation, but I suspect this wing-flicking antenna-waving act creates visual jolts which help to startle potential victims into movement, and thus make it more likely that the wasp will spot them.

If you look closely - click on the photo to expand it - you can see the poor spider's eyes peering out. It is doomed, and the end will not be pleasant. The wasp injected it with neurotoxins which cause paralysis, but the spider is very much alive. It is being dragged to a burrow that the wasp has pre-selected for interment.

This was far too good an opportunity to let go, so we carefully followed the wasp as she tugged her victim along. I figured the burrow would be very near at hand. It wasn't. We tracked the wasp for approximately 130 feet, and this hard-working insect rapidly tugged its prey over branches, sticks, leaves and all manner of obstructions. Every now and then, she would stop and essentially wander about a small radius from the spider, presumably picking up a pheremone trail or some other clue to ensure that she was going in the right direction.

It took her almost exactly 15 minutes to cover the 130 feet from kill site to burrow, and the route that she took was remarkably straight. We were impressed. The spider is as big as the wasp, and presumably equal to in weight if not heavier. A truly herculean feat, moving it as far and as rapidly as she did.

Finally, the wasp reached this small hole and wasted no time pulling the spider in. She was in there when I took this photo. Although we can't see it, she is laying an egg on the paralyzed spider, then probably sealing it in with soil. Eventually, that egg will hatch, and the grub will have fresh meat, eating the living spider. All goes well, and ultimately another big beautiful black and yellow wasp will emerge from the spider's grave and start the process again.


A video showing the general lay of the land. Nice bit of luck for us, and the wasp, but certainly not the spider.


donaldthebirder said...

I saw a spider wasp just yesterday while at my cousins. It was flying around her front porch with a dead Black Widow spider. I told her this is probably one wasp you'll want to keep around.

Bob Scott said...

Wow! I saw one of these guys on a hike yesterday. Must be the season for them. But I never thought to stop and watch. Sure will next time!

Jana said...

Poor Spidey.

My daughter could use a few of these wasps. She just moved to the East Bay area in CA and is finding all kinds of spiders in her apartment. Let's just say she's freaking out a little bit.

Jack said...

Thats really nice picture with wonderful video....Thanks for sharing with us..
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