Greetings, BugFans,
The BugLady always enjoys encountering these big, handsome, velveteen spiders—one of them shared a fondness for her rhubarb patch recently. She has written in the past about the admirable six-spotted fishing spider, a member of the Six-Spotted Fishing Spider (family Pisauridae). Today’s BOTW features a member of the same family who goes by the common name of nursery web spider (Pisaura mira).
Nursery Web Spiders
Nursery web spiders get their name from the protection a female provides for her egg sac. She carries it around in her jaws until the eggs are near hatching (she has a back-up—a strand of web also attaches the spider’s egg sac to her spinnerets); then she hides it and spins a silken enclosure around it, roping in some vegetation. She will defend her brood until they disperse after their first molt.
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They look a lot like wolf spiders, except when you gaze into their eight eyes, which are a different size and arrangement than a wolf spider’s. As a general rule, wolf spiders are more commonly found on the ground and nursery web spiders above it; and although wolf spiders also tote their egg sacs, they attach the egg sac to their spinnerets, at the rear.
Nursery web spiders are found in tall grass, along wooded edges, and in shrubs (and sometimes houses) from the Atlantic into the Great Plains (the species is also found in Europe), and one spider expert speculates that Pisaura mira may be one of the most common spiders in eastern North America. They are large, with up to a three-inch leg-spread, and are variably earth-toned: Spider – Pisaurina mira, and Pale Spider – Pisaurina mira (plus this aberrant teal-colored individual and her young Blue Spider – Pisaurina mira, which look like those experiments where you put a celery stalk in water and food coloring).
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Although they spin silk, Nursery web spiders do not make webs to snare insects. Their eyes are excellent motion-detectors, and they feed on small insects that they find as they wander the landscape.
As the BugLady mentioned last week, spider courtship is a tricky dance; in the spider world, a female is as apt to eat her smaller suitor as mate with him (great throwaway line in Wikipedia, “except where the male is so much smaller that he is not worth eating”). Some sources say that a female Pisaura mira is not generally known for that behavior, and other sources describe the species as cannibalistic. The male takes no chances.
They mate suspended by a dragline, and before mating, in mid-air, he secures her front two pairs of legs with silk (the silk binding is called a “bridal veil” and, speculates one researcher, is possibly pheromone-laden) and then he wraps his legs around her other legs (she can shed the bridal veil easily after he leaves). This allows him not only to deliver a webbed packet of sperm to her, but then to deliver a second, increasing his chances of fatherhood (and something she would not tolerate if she were unencumbered). Researchers have demonstrated that male Pisaura mira that are larger and have longer legs have better breeding success (and a lower mortality rate). Males of some species of Pisaurids first present her with a gift of a dead insect (whether to feed her or distract her is not known) and will eat it if she doesn’t.
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Nursery web spiders overwinter as spiderlings and are full-grown adults in late-spring/early summer when the big orb weavers that will impress us in September are still very small. Larry Weber, author of Spiders of the North Woods, writes that he sees Pisaura mira, occasionally, “on the surface of the snow; usually in early winter in swamps.”
As always, in her “nursery web spider” search, Google produced for the BugLady sub-searches on “nursery web spider bite” and “nursery web spider poisonous” (Google offers these topics for some pretty innocuous critters, a commentary on our apartness from nature). Nursery web spiders are poisonous with a small “p,” with venom powerful enough to kill their prey (strong enough, in fact, to kill a smallish fish) but not strong enough to endanger to people or pets.
The BugLady