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Posts tagged “Araneidae

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.


Spider Spinnerets

All spiders are capable of spinning silk, regardless of whether they use it to spin webs and trap prey or not.  Egg sacs, drag lines (so they can find their way home), drop lines (to catch them if they fall) egg cases and transportation (young spiders disperse by “ballooning” as the wind catches their silk and carries them off) are some of the other functions silk plays in the life of a spider. Silk is extruded through nozzles called spinnerets located near the tip of the abdomen. Typically a spider has two or three pairs of spinnerets.  Each one is the exterior tip of an interior silk gland and has a valve which can control the thickness and the speed with which the silk is extruded.  The different glands produce different kinds of silk used for different purposes. The spinnerets work independently for some functions, and together for others.  In the photograph, the black and yellow argiope is turning her grasshopper prey around and around as she produces a sheet of silk in which she wraps it.  Most, if not all, of the spinnerets are in use.