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Posts tagged “Black and Yellow Argiope

Some Spiderlings Hatch in the Fall

antmiimic spider egg case 013Have you recently noticed a roundish, flat, papery, 1/4-inch diameter, metallic-looking structure adhering to the top of a rock? If it has tiny bumps in the center, chances are good that it’s a spider egg sac, most likely that of an antmimic spider (spiders resembling ants that often prey on ants), specifically one in the genus Castianeira. One would assume that the contents of the sac that were causing the bumps were eggs that were going to overwinter and hatch once warm weather arrives. This is true for a majority of spider egg sacs, but some, including those of Black-and-Yellow Argiopes and antmimic spiders, hold spiderlings that have already hatched and will remain in the sac throughout the winter. As long as the temperature stays cold, the spiderlings will be safe and secure until spring. If we have periods of cold interspersed with periods of warmer temperatures, or an exceptionally warm winter, the spiderlings will become active when the thermometer rises, and, not having any insects to eat, will be forced to devour each other.

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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.


Silk Rainbow


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.