Naturespeak A naturalist's view of the world

July 17, 2007


Filed under: Uncategorized — wykes @ 10:06 pm

Spiders are certainly the subject of many human dreams, but I wonder if spiders themselves have dreams. Perhaps they would see themselves weaving a hopelessly entangled giant web or engaged in a continual search for their eighth shoe.  Screaming people or the sight of a bathtub filling up with water would certainly qualify for their nightmare fare. Among more educated spiders, however, one creature looms large as the scariest and most nightmarish of all – the Mud Dauber Wasp.  Dauberphobia is prevalent in the Arachnid set.

  There is nothing about Mud Dauber Wasps to frighten us humans.  Though these large active wasps are common around our dwellings, they are not colonial or aggressive and rarely sting.  The worst thing they do to us is to plaster mud cakes under our eaves and porches – this is more a visual nuisance than a true problem.   There are three basic kinds (Organ Pipe, Blue, and Black & Yellow), but probably the most common is the well named Black & Yellow Mud Dauber.

  I encountered a few B & W’s, as I’ll refer to them, engaged in setting up a spider nightmare the other day. Take a look at this portrait of one of these thin-waisted wasps. They are about 1 ¼ inch long and have satiny black bodies with bold yellow markings. I took this shot after inching as close as I could to these visually acute little beasts. They have excellent vision and were alarmed at my every move.  True to their nature, they never ventured to sting or act aggressive. The wasps were gathering mud from the edge of a drying pond. Once satisfied that I was nothing more than a giant rock, they would select the wettest mud and proceed to lower their jaws to the surface and gather in a few bites of the material with their mandibles (see here).  Once a tiny mud ball was firmly in grasp, they launched into the air and made a beeline – actually a waspline – to their nests.

  Sceliphion caementarium is the scientific name of this species.  The second part of the name is Latin for “mason, or builder of walls,” and these tradesmen use mud to construct walled chambers for rearing their young. The structures are placed in a weather protected space beneath an eave or rock overhang. They consist of several side by side 1 in. by ¼ in. chambers which in turn are plastered over with a rough coating of adobe to form a fist sized lump’o mud on the wall. Here’s a shot (by Margaret Jones Young) of a female in the process of building a chamber wall. Each mouthful is carefully palpitated into a rope of clay that is laid down strip by strip – something like a potter using the coil method to make a pot (not really, but that is the only analogy I can come up with).

  Akin to our whistling while we work, B & W’s have been shown to “sing” and produce a humming vibration while daubing the mud. This liquefies the material and makes it pliable. After numerous back and forth trips from the mud quarry to the building site, the wasps complete their task in relatively short order. As each chamber is completed, the empty space within elicits a shocking change in behavior.  The B & W’s become hunters – spider hunters.

  As a rule, daubers feed on plant nectar, but their sudden desire for eight-legged prey is a maternal thing. But, unlike the human mom-to-be desire for pickles and ice cream, this arachnophilia doesn’t involve actually eating spiders. The spiders are for the baby wasps. The males, by the way, stick to their nectar fare since they don’t participate in the house building or kid raising stuff.

  For the balance of the day, a female’s sole task is to track down and gather in as many spiders as it takes to fill up baby’s chamber. It takes anywhere from 6 – 25 spiders to adequately stock one larder cell. A single egg is laid on the body of the first spider crammed into the void and the whole chamber is sealed with a mud plug once the space is topped off.

  I followed the exploits of one of these huntresses to see if I could catch her in the act of nabbing a spider.  She was a gal on a mission and it was hard to keep up. Every nook, cranny, and website was browsed.  Sensing prey sealed away in a silken retreat beneath a picnic table, she launched an earnest attack to get at the occupant. I managed to take a photo of her as she attempted to flush the spider by pulling on the silk walls and poking her head into the end of the chamber. The spider was having no part of it and resisted the effort to expose herself. It is the nature of most spiders to drop out of the web or rest chamber in order to escape.  As it turned out, it was sizable orb weaver and much too large for the wasp, so she gave up after several minutes.

  I lost track of this particular female, but I know that eventually she would be successful. Oddly enough, this spider searching doesn’t result in the immediate death of the spider. The B & W stings her charges with a paralyzing dose of venom, not a lethal one. The stunned spiders are carried back to the mud chambers and packed like sardines within. When the mud door is plastered into place and total darkness envelopes the chamber, the spiders remain alive but unable to alter their fate.

  Recall that the first paralyzed spider in the mud cell was gifted with a single wasp egg.  After a few days that tiny egg hatches into a very hungry little wasp grub that begins to consume the freshly preserved spiders. The grub has no legs or eyes, but crunching mandibles equip it for the task at hand. One by one the spiders are eaten alive – slowly and inexorably.  Take a look here at a grub exposed within its chamber and this shot of a nearly full sized grub (5/8 in. long) with what remains of its paralyzed fare. By the time the last spider is polished off, the grub has reached full size and pupates before emerging as an adult wasp.  All that remains in the old chamber are the hollow dried skins of spiders.

  Such a scenario would startle even the most stalwart of sleeping spiders into a sweaty awakening. 

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