Ok, first post, guys.
Was out the other day in some rare San Diego open space with my son and, being the hyper-observant amateur naturalist that I am, found a round shape on the ground. Figured out it was a trapdoor spider's burrow, but was amazed at how large they actually are. The TV documentaries didn't show scale well? 1 inch across! This burrow looked old, the door was nearly separated. There were spider babies around. I looked around and found another burrow only 1 meter away. This one was nicer. It was closed, but had a oval hole in the door. Wasp? Went back home and got on the computer to learn more. Grabbed my camera, a slender piece of wood, some thread, and a small screw, and this time returned to the well-marked site with my daughter. We measured the depth of the 2nd burrow by dropping the screw/thread combo down the hole, marking the length and taking a pic. The quarter shows the scale. Completely fascinated, I started looking for a "live" burrow and spider. Couldn't find a damn one! Not one. I searched the area for an hour or so. How could there be 2 burrows within 1 meter, and none other within 20 meters? Maybe the live burrows are better kept up and thus better hidden?

For a first, post, NICELY DONE. We have a few folks who are locals, maybe they'll chime in on species, but yes, the occupied ones are very well kept. I've seen them so well hidden that you can look right AT them and not see them in an aquarium!

Welcome to the ATS discussion boards, hopefully we can help you and your interested son find more information, and maybe break into the hobby a bit more?

One thing I'd add is I don't know if you can be sure the burrows are empty. There could be a side passage or a false bottom, and some species may even build a second tunnel and door. Your screw might just be reaching the first turn! However, the hole in the door does suggest a predator. Some species will actively pull down on the door from the inside if you try to force it open, and I know someone who claims that a Ummidia sp. bit him THROUGH the door! Others just seem to retreat to the farthest reaches if the burrow.

Trapdoor spiders will use all manner of debris to disguise the door, so it is possible that rain has cleared this away from some inactive burrows.

1" is indeed a big burrow width! I think you're looking for a fairly substantial-sized spider!

Wade

Quite a nice first post, indeed!

I live just north of LA towards the desert, and I call this area "trapdoor heaven".
We see burrows all the time on our hikes, and the size matches about your finds.
The species is most likely Bothriocyrtum californicum, which is what we find up here.

One thing about telling if there is still a spider inside the burrow is how white the silk is on the inside of the trapdoor lid. White or slightly tan color points to a used burrow while a darker shade of brown tells you it's abandoned or the resident has perished. Even if the lid was breached by a predator the spider would he started repairs on this vital part of the burrow almost immediately if it survived.
Newer burrows and those in use are flush to the ground, which makes finding them a little harder.
I have a gazillion pictures of new and old burrows and I'll try to find and post them asap. Until then, do a search for my posts with trapdoor burrows and you'll see a bunch of pictures from the last years.

Welcome to the ATS, glad you found us!

Here are a few burrow pictures, all active burrows:



For size:


Well hidden




Opened the lid by gently prying a knife point between the burrow rim and the trapdoor. The white silk shows that someone is home and the two tiny holes are where the spider holds the door shut with it's fangs


After a remodeling project: the old door has been thrown out and replaced with a bigger one above


This is a prime example for the shape of a trapdoor: the "hinge" is straight to allow the door to open without resistance while the door itself is somewhat oval shaped


Ready to see if someone is home:


A washed out burrow after a big rain. This one hasn't been opened in a while


Yup, active burrow


Blending in with the ground


Unopened


- and opened

That's wonderful Anette! Trapdoors are an extremely interesting and overlooked group of spiders! Hopefully I'll get into grad school over in CA and be able to play with these guys more regularly!

Habitat photos?

Thanks for sharing Anette, I trust things are well with you!

Zach