Spider Egg Sac

If like me you occasionally flip over rocks and such to see what might be lurking beneath, then you’ve no doubt seen things like this:

6mm | January 19, 2011 | Armonia Nature Preserve, Limon Province, Costa Rica

I’m pretty sure this is the egg sac of some sort of spider. It was underneath a small rotting log.

I usually just carefully put things back the way I found them. Curiousity got the better of me this time. I peeled away the egg sac and carefully opened it. If you’ve ever wondered what’s inside, here’s the answer.


Each one of those eggs are less than a millimeter in diameter. There were probably ten or so.

I put the egg sac back where I found it. With the eggs now exposed though, the’ll probably end up being eaten by something.

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3 Responses to Spider Egg Sac

  1. james says:

    Hi Troy,

    I live in Northern Ireland, I was going on a day trip up the river Bann and noticed an all black spider with 4 red dots on its thorax, from left to right. It was guarding three of theses sacs. I found it on a stone on the beach, I’d never seen such a spider before or egg sac. Your photo most resembles it.

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