An online resource based on the award-winning nature guide

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.

8 responses

  1. viola

    Remarkable!!! both the facts of the spiders life cycle and the one who photographs and brings us these fascinating stories.

    September 19, 2012 at 1:49 pm

  2. Susan Holland

    Yet another day when I have learned something new thanks to Mary! Great photographs, as always.

    September 19, 2012 at 2:07 pm

    • No family prejudice, of course 🙂 Thanks, Titus.

      September 19, 2012 at 2:52 pm

  3. Neat!!! Thanks for sharing these cool photos. And I would not have opened an egg sac either. Although I am often curious, I prefer to let nature reveal itself. 🙂

    September 20, 2012 at 3:00 am

  4. Have almost walked into the spider web when puttering around but the zigzag appeared at the last minute. I really love to have this spider in my garden, but I’ve lost it – too many praying mantises I think. Thanks for the great work you do, Mary!

    September 20, 2012 at 1:38 pm

  5. The photo of the torn open egg sac looks like a constellation. Amazing!

    September 21, 2012 at 1:30 am

  6. I’m so glad I read this when you posted it because today I was about to bring in a rosemary plant that has been outside all summer when I noticed this same egg sac. I might have thought it was a gall instead! I’m going to see if I can detach it without harming it and leave it in a shrub to overwinter. I certainly would not have been happily surprised to find several hundred garden spiders in my livingroom!

    September 26, 2012 at 9:00 pm

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