The Egg Sac Gallery

Spiders lay eggs. Depending on species, they can lay thousands of eggs or just one single egg as is the case with the tiny spiders in the genus Monoblemma (found in tropical Africa and tropical Americas). The featured image above shows the egg sac of Argiope aurantia (AKA banana spider, garden spider, Steelers spider) on the left and a wolf spider (Rabidosa punctulata) egg sac on the right.

Magnified photo of spider eggs inside a sac. 

The female spider produces a mat of silk, the eggs are deposited on the mat, and the whole thing is wrapped up to look like a sac. Some sacs are paper discs. Some look like fluffy balls, some look like debris, and some are merely held together by a few threads. Egg sacs may be abandoned or protected while the eggs are developing. Wolf spiders and fishing spiders carry the egg sac around with them. Some spiders make a silken tent and hole up with the eggs until they hatch. Spiders can produce several eggs sacs per season. Spider egg sacs are nearly as diverse as the spiders themselves!


Wolf spider Trochosa terricola with egg sac in exposed “nursery tent”.
This tiny brown paper bag is the egg sac of the ray orbweaver, Theridiosoma gemmosum, a spider that is only 2.7 mm from head to spinnerets. The egg sac is suspended from a thread.
A spitting spider with its eggs loosely wrapped with a few silk strands. She will carry the eggs until they hatch and then the spiderlings are on their own.

While hiking at McConnell’s Mill State Park, I came across “cave spiders” that I never saw before. The cave was between some big boulders with camel crickets all over the place as well. Perhaps camel crickets were the main menu item for these spiders. I took a bunch of pictures and was later able to identify the spiders as Meta ovalis, the cave orbweaver, using an egg sac as confirmation.

Meta ovalis with its cotton swab egg sac.

Some spider egg sacs that you may already be familiar with are woven by our common house spiders. Teardrop-shaped, papery, brown sacs, about the size of a pinky nail, belong to Parasteatoda tepidariorum. These spiders are common in porch corners and garages. Then there’s my roomies, Steatoda triangulosa AKA The Vacuum Evaders which create perfect, cottony spheres.

Common house spider, Parasteatoda tepidaroirium, with 4 eggs sacs, one of them with spiderlings!


Spent egg sac of Steatoda triangulosa…from under my microwave stand. This means there are at least four more in the house somewhere…

Euryopis funebris4

Cobweb weaver, Euryopis funebris, an ant-eating specialist, and her spiky egg sacs.

Spiders are dioecious which means there are male and female. Check out The Birds and the Boxing Gloves? for more info on how to tell them apart. Even though there are male and female, there have been cases of female spiders giving birth to all female spiders, no males needed (parthenogenesis). Spiders may also lay a bunch off infertile eggs that just never hatch. This has happened with my captive immature female spiders who have been isolated from males. Suddenly, an egg sac appears. I’ve opened these egg sacs just to find the eggs hard and clumped together like a stone.

Black widow (Latrodectus mactans) egg sac. The eggs are unfortunately infertile since I caught the spider while she was immature and have had her in captivity the whole time – no males.
A western lynx spider with its disk-like egg sac. You can see the eggs darker in the middle. This spider produced two infertile sacs right before she died in captivity. The egg case is about 4mm across.
This is a cool cross section of the funnel weaver sac (Agelenopsis pennsylvanica). You can see the eggs at the bottom then a negative space and then more silk. Mom is on the premises!

Once the spiderlings hatch, they stay inside the safety of the egg sac for their first molt and then bite their way through the silky mesh. Wolf spider mom’s tear open the sac for the spiderlings and they quickly climb onto her back. As of this writing, I have the large, yellow egg sac of the orb weaver Neoscona crucifera. The spiderlings have hatched, but are still in the sac. I can see them moving around when I put a light underneath the container. It’s a cold January here in Pittsburgh, most all spiderlings would naturally come out in spring. Since they’re in the heated indoors, I’m guessing they’ll come out sooner. We’ll cross that bridge when we get there!

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Domed sac of Neoscona crucifera.
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Caught in the act! A spider from the Castianeira genus (Ant-mimic spiders) putting the finishing touches on her egg sac. This photo was taken in summer.

I have just touched briefly on the diversity of spider egg sacs. There are many more like the vase-shaped bolas spider sac and the brown widow’s spiked sphere which resembles the ball on the end of a flail. Brown recluse egg sacs stand out under black light and the pirate spider’s sac is bright orange. It’s like gift wrapped spiders!

Check out this video of a  black widow laying eggs

And just for fun, here’s a link for spider egg donuts

16 thoughts on “The Egg Sac Gallery

Add yours

  1. I’m watching a house spider that has made three egg sacs over a period of a couple of weeks.

    The first sac has spiderlings on it. I never see them moving, but I can tell they’re shifting around from day to day. Any idea how long spiderlings hang around?


    1. Hi! I assume by house spider, you mean the Theridiidae family? Multiple egg sacs sounds about right! I’ve noticed with rearing widow spiders that the spiderlings will stay clumped around the egg sac for about a week or so and then they slowly start to disperse. For Parasteatoda, I’m guessing a similar “hang” time, say 8-12 days? Could be weather dependent, too. Colder weather may = slower dispersal.


  2. Hey i found an egg sac almost 3 inches in diameter in an old truck i bought.How big can egg sacs really get.There were 2 the 2nd on was a bit smaller but still almost 2 inches in diameter.Dont think Black Widow but what has a sac that large ?


    1. Hey! What’s your location? That way I would know what spiders you have around. And pics are very helpful! It could be an insect cocoon or maybe something else? I’ve never seen a spider egg sac that large so I’m not familiar! Send photos if you can!


      1. Lee, I’m unable to give a shot at an ID without a photo, but we can eliminate some spiders – it’s too large for a widow. Wolf spiders carry their sacs with them, so we can nix them. Considering your larger spiders, like the Olios genus (giant crab spiders), the mom spider will guard the sac, so if no mom, then it’s probably not that. Plus their egg sacs are kind of flattened. Tarantulas are going to burrow. Could you be so lucky? My best guess with the limited info is some type of large orb weaving spider?? Here’s a link to some photos that you can try and match to:
        You can always keep em in a jar and see what comes out!


  3. Trying to identify a spider based on the egg sac only (left in web, 2 sacs, yellowish, spikes all over). This is the only guide I’ve been able to find that is actually helpful, with pictures and descriptions. Unfortunately, doesn’t contain any pictures that match mine. Do you know where I might find more information similar to your guide, but more variety of species? Everything I find is either behind a sign-in or ends with “call us to do pest control” (but no actually helpful information to identify what I’m up against).


    1. Hey! The spider ID world would greatly benefit from a comprehensive egg sac guide, for sure! If you’d like a hard copy resource, I would recommend the Common Spiders if North America by Sara Rose. She includes a lot of spider egg sac pics. I can’t open any photo attachments…been looking into that glitch, but based on your description of “yellowish spikes all over” it sounds like it could be a brown widow sac (Latrodectus geometricus) if you live south. Try looking that up and see if it matches!


      1. Thank you so much! I will definitely see if I can find that resource, as it may be easier for me to read in hard copy form. But I must say, I *love* how you have such a great guide here!


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