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Archive for September 19, 2012

Black-and-Yellow Argiope Egg Sacs

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Black-and-yellow Argiopes  (Argiope arantia), often referred to as “garden spiders” are one of our most conspicuous orb web-spinning spiders — their webs are often two feet in diameter, and female spiders measure an inch and a half (males are about ¾”).  At this time of year, they (and many other spiders) are busy mating and laying eggs, which the females wrap in a multi-layered “sac” of tan silk that resembles a large marble in size and shape.  Inside a Black-and-Yellow Argiope’s egg sac are between 300 and 1,400 eggs.  In northern New England, the eggs hatch in the fall and the spiderlings overwinter inside the sac, where they remain dormant unless the weather warms appreciably (in which case they become active resort to cannibalism, there being no insects in the sac).  I have often wondered exactly when the eggs hatch, but have chosen not to tear open an egg sac in order to find out.  A bird, the predominant predator of spider egg sacs, did the deed for me recently, and tore into one, exposing the contents, which I photographed.