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What’s Inside A Spider Egg Sac This Time of Year May Surprise You

10-2-17 black and yellow argiobe egg sac2 IMG_5913

Some species of spiders (including wolf and jumping spiders) overwinter as young adults and mate/lay eggs in the spring. Many spiders, however, mate in the fall, after which they lay eggs and die. Their white or tan egg sacs are a familiar sight at this time of year. One might assume that these species overwinter as eggs inside their silken sacs, but this is rarely the case as spider eggs can’t survive being frozen. Spider eggs laid in the fall hatch shortly thereafter and the young spiders spend the winter inside their egg sac.

Although egg sacs provide a degree of shelter (the interior is packed with very fine, very soft silken threads), the newly-hatched spiderlings do have to undergo a process of “cold hardening” in the fall in order to survive the winter. On nights that go down into the 40’s and high 30’s, these young spiders start producing antifreeze compounds, which lower the temperature at which they freeze. By the time freezing temperatures occur, the spiders are equipped to survive the winter inside their egg sac – as spiderlings, not eggs.  (Photos:  Black-and-Yellow Argiope, Black-and-Yellow Argiope egg sac, Black-and-Yellow Argiope spiderlings inside egg sac)

6 responses

  1. Kathryn

    I bet one of those egg sacks would be a really terrific treat for a bird or somebody this winter.

    October 2, 2017 at 10:43 am

    • Yes, the one I photographed was one that a bird had already pecked a hole in!

      October 2, 2017 at 5:44 pm

  2. Susannah

    Hello Mary,

    I love your posts (and don’t worry at all about occasional confusions of species or naming or whatever — we naturalists/nature lovers all do that). But today I received two at the same time. (See screen-grab below of the two emails in my inbox.) Is there some glitch with the email system? Just wondering, and I thought you (or wordpress dot com?) might want to know. Thank you for all your beautiful photos and posts.

    Best, S

    Screen-grab of double email

    October 2, 2017 at 11:42 am

    • Thank you, Susannah! I am aware of the duplication and it can be remedied. Your letting me know is much appreciated!

      October 2, 2017 at 5:45 pm

  3. Kathie Fiveash

    What a cozy crowd inside the egg case! I wonder if the spiderlings have any recognition of their siblings when they disperse after that long winter snuggle. I know most spiders have smell and taste organs on their legs.

    October 2, 2017 at 12:10 pm

  4. judilindsey


    Could nature get any more fascinating than this! Thank you for your constant gifts of knowledge – packages in easy to digest bundles!

    Judi 🙂


    October 2, 2017 at 6:03 pm

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