Thursday, July 25, 2013

Web of Intrigue

Fog hung thick over the lake and early morning light filtered through the trees. I bent low in front of my favorite lakeside window, touching my toes and enjoying the stretch. As I rose up and reached my arms overhead, dark shape in the corner of the window caught my eye. There, on the outside of the screen, was a very large spider. Including legs, it had to be at least two inches across.
Spiders are amazing creatures, but I have a bit of innate fear of the largest ones. Still, in the spirit of yoga, I silently appreciated this spider for eating some of the bugs trying to sneak into the house to eat me (mosquitoes!). Then, I glanced at the adjacent window and saw the silhouette of a spider twice the first one’s size!
Female dark fishing spiders are the largest spiders regularly found in the Northwoods. This particular female was about as big as they come, with a legspan of almost four inches!  The first, smaller spider must have been a male, since they are about half the size of females. As their name implies, most fishing spiders live near water. Dark fishing spiders stray farther from water than other species of fishing spiders, and are often found near docks, in wet woods, and in basements.
With dark and light chevron patterns on their large, oval abdomens, and dark and light stripes around their legs, these spiders are quite striking. My roommates had assumed these were wolf spiders, but wolf spiders don’t get as large overall, and they have much bigger eyes. The difference in the eye size of the two families relates to their hunting techniques.
Wolf spiders are visual hunters who pounce on prey by day and night. Fishing spiders use a range of vibration-detecting organs, including very sensitive hairs on their legs and feet, to sense prey. I think my spiders were sensing vibrations on the window screen. Other species of these hairy hunters sense their prey’s movement through vibrations on the water’s surface. Their eyes are only secondary, and they do not spin webs. 
Dark fishing spiders do, however, spin a web of intrigue with their odd mating habits. The reproductive techniques of most spiders seem a little odd from our human perspective. Male spiders produce semen in testes on their abdomen, then spin a “sperm web,” fill it with sperm, and suck the sperm up into their “pedipalps,” which are antenna-like sensory organs near the spider’s face. The sperm inflates the pedipalps.
The male does the appropriate love dance, climbs up on the female, inserts one of his pedipalps into her genital opening, and deposits the sperm.
Here is where the dark fishing spider gets unique. A recent study revealed that, for the male, mating is like committing suicide. “The act of sperm transfer is triggering this cascade of death,” said Steven Schwartz, a behavioral ecologist at the University of Nebraska. “Once that button is pushed, it’s lights out.” The male dark fishing spider’s legs curl up and he becomes immobile.
If the male dark fishing spider is lucky, the female will eat him, become satiated, and not mate with other males. This benefits the deceased male by ensuring that he will be the father of her spider babies. If he isn’t lucky, he dies within a couple of hours and the female goes on her merry way.
As the rising sun illuminates my window, I see the huge spider resting there, and the smaller male nearby, in a whole new light. I respect the complexity of a relationship I can’t fully understand.
As Buddha says, “Have compassion for all beings, rich and poor alike; each has their suffering.”

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