Barricade-Building Spiders
On July 8, 2025, I was seeing a lot of these spiders that were building barricades out of small stones and other debris. The spiders were living in the crevices between the concrete blocks that make up the big retaining wall alongside part of our road. The blocks are about 2 feet tall and 3 feet long, and the crevices look like this:
The sizes of the barricades varied a lot, ranging from basically a fort,
(incidentally, the part at the bottom appears to be a caterpillar that the spider is eating)
to an almost token little object that she can hide behind.
The barricades are not necessarily gravel, this one has a maple seed;
And this one is very much into mixed media.
In a lot of cases, it just looked like a swarm of little pebbles levitating in the air.
They seemed to prefer objects that they could either hide behind, or that were about the size and color of the spider and could therefore act as decoys.
They seemed to vary a lot in how much they wrapped up their prey, it probably depended on how much it struggled.
So, anyway, I am reasonably confident that these spiders are all the same species, most likely one of the two species in the genus Parasteatoda. The more common of these two species is Parasteatoda tepidariorum, which is often referred to as the “common house spider”. However, based on the barricades and shelters that they are building, I think they are more likely Parasteatoda tabulata, because P. tepidariorum is not actually known for doing that. BugGuide says that for P. tabulata, “the females of this species make a retreat which is covered with pieces of twig, grass, stone, earth, or prey remains. The retreat is suspended near the very middle of the web and the female is often found inside it, sometimes with one or more males in close proximity. Egg sacs are placed inside the retreat.”
And that is in fact exactly what we are seeing here. Several of those retreats had egg sacs, and here is one with a male in close proximity:
You may note that the male is a lot thinner, redder, and has spindly legs, which also agrees with the pictures of the males on BugGuide.
I thought it was interesting that most of these barricades were actually quite high up, with the nearest source of bits of sand and small pebbles being a foot or so lower than the barricades. It looks like the spiders crawl down there and winch up appropriate rocks, which actually sounds like quite a bit of work. On the plus side, the barricades are probably pretty good protection against marauding wasps, many of which either directly parasitize spiders, or paralyze them and drag them back to their nests to feed their grubs. If the wasp has to spend several seconds either working its way through a barrier, or trying to sort out the decoy pebbles from the spider, then the spider has a much better chance to escape. And what I observed several times when I bumped the web, was that when disturbed the spider would drop straight down to the ground below and disappear.
Anyway, there were a lot of these spiders, and about half of them were actively feeding on prey they had caught, so overall this looks like it works well for them.