The Trapdoor Spider Came In From The Rain

With streaks of lightning and claps of thunder an October storm brought well-needed rain to Southern California. While the rest of the country is preparing for the white blanket of winter, our native plants are waking up from a dormancy that helps them survive the hot dry breath of summer.

In the rain the mallow rejoiced and unfurled new blooms.

The katydid rode out the storm on her rose perch. While the days are growing cooler, she still has a month or so to enjoy the new growth.

One hillside resident, however, did not welcome the rain. Damp and homeless, she wandered in under the kitchen door seeking shelter. She stumbled into the web of a cobweb spider and was stuck there about an inch off the ground.


I was startled at first by the size of this visitor. Including her legs, she is about the size of a quarter. At first I thought she might be a young tarantula, but upon closer inspection she has the glossy brown cephlothorax of a trapdoor spider. While a relative of the tarantula, this spider has a softer, more vulnerable appearance. She’s kind of like that geeky cousin with the pale skin that seemed allergic to the sun.

The trapdoor spider colony on our hillside has included 17 locatable and occupied borrows. I haven’t counted in resent months, but it’s usually easy to spot 4 or 5 at any given time. While chance encounters have occurred when underground burrows were mistakenly dug up, I have never seen one of these homebody spiders out walking around.

I’ve seen them holed up with a brood of offspring. Baby trapdoor spiders.

And last spring, heavy rains caused one poorly placed burrow to be damaged. Damaged trapdoor spider burrow.

Did this young female trapdoor spider loose her home in the rain? There doesn’t seem to be any major mud flow areas in the yard.

Was she uprooted by the gopher that has been tunneling on the hillside and relocating dirt where no one wants it? It could be. But if she came from this far section of the yard, she walked at least 50 yards to get to the back door.

Maybe she lost her home to a foraging skunk some time ago and had yet to find a suitable hole when the rain came? Yet, she seems plump and healthy, not a spider on the edge of survival.

A female trapdoor spider spends her whole life in the protective confines of a tunnel. Walking around, she is vulnerable to the California towhees hunting in the leaf litter, skunks prowling at night, and even the wolf spider that seems to have devoured all of the cobweb spiders in the chicken house. While a male might go out looking for a mate, the large rounded abdomen and small pedipaps between her front legs and fangs tell us she is indeed a female.

What is this shy young girl doing wandering about in the big wet world? I don’t know.

While it is fascinating to see out of her tunnel, the yard needs her as a predator and she needs a natural location where she can build a comfortable tunnel burrow. When the rain stops and night falls, I’ll return her to the hillside where she belongs.

Damage to Homes After California Rain

A stroll through the yard revealed that the recent rains affected residents in the yard even more than they affected us. Oh sure, we were concerned with diverting water and the mud flow that came down the canyon. Mud.

But this trapdoor spider had the door of her home slide down the hill and completely off her tunnel.


If you look closely, however, you can see she is connecting a new tunnel to the soggy door. Apparently, the well-constructed door is more difficult to replace than the tunnel. Rather than make a new door, she is building a new home beneath the relocated door.


Even the slightest erosion of the clay substrate reveals the soil that has been reinforced by the trapdoor spider's handiwork. Here a burrow door sticks up, slightly raised, from the surrounding level of the dirt. This spider didn't loose its home, but some of its security has been temporarily washed away. Trapdoor spiders



For both spiders the ground, and therefore the trapdoors that protect them, remain soggy and soft. With their tunnels exposed and damaged, they have suffered much more than we have from the week-long rain.

Meanwhile the green lynx spider has survived, but her offspring have not. Will she lay another egg sac? And the preying mantis eggs laid in November? They remain safe on the twig where their mother laid them.

Eight inches of rain on a southern California hillside over 6 days can be a challenge for the creatures living on that hillside. We humans tend to think only of ourselves when we are faced with challenges or discomfort. But extreme weather events can be life threatening for smaller creatures. They are directly connected to a small area of habitat. For them the ramifications of climate change are more immediate.

Trapdoor Spiderlings and Hummingbirds

Babies, babies, babies. Imagine my surprise when walking through the yard yesterday I discovered an open trapdoor spider burrow. When I looked inside I found 100 to 200 spiderlings.


Down in the burrow there were BB-sized bumps on the wall of the tunnel. When I brushed them slightly with a piece of straw, the bumps moved. A flashlight revealed the ‘bumps’ were the abdomen’s of baby trapdoor spiders.

Here is where the tale gets unusual, the trapdoor that should have been closed and protecting these young spiders had been surgically removed. It was laying intact beside the opening. There did not appear to be any obvious signs of force to open it. It’s silken hinge had just been neatly severed.

About four inches to the left was another trapdoor spider burrow of the same size tightly sealed, its resident safe behind its closed door.

Was the door to the spider nursery removed by a predator? If so, there were a lot of spiderlings that not been eaten. In fact I just checked on them, and 24 hours later, they are still clinging to the side of the tunnel, though some seem to be down lower in the tunnel, probably to escape the heat of the day.

Was their mother eaten? I don’t know. If so, will these spiderlings starve or be eaten without her protection?

Or is their mother living in the tunnel next door? Perhaps this was the nursery burrow. I have noticed that a number of larger trapdoor spider burrows seem to have an equal-sized neighbor right next door.

Perhaps these spiderlings are just big enough be introduced to the world and mom has literally opened the door for them to go. I really don’t know and haven’t been able to find anything that might explain this mystery.

I will keep an eye on them and see if they do start to head out on their own.

Meanwhile the Allen’s hummingbirds are growing. Their feathers are coming in and their beaks are beginning to elongate. (When they hatched and first week)

The spiderlings have been developing all winter, the hummingbirds will be out of the nest in weeks. Amazing what you can run across on a warm spring day.

The Gift of Trapdoor Spiders

Not every spider builds an aerial masterpiece like Charlotte in “Charlotte’s Web.” Many spiders stay close to the ground and some, like tarantulas and trapdoor spiders, live underground.

Trapdoor spiders are found worldwide, from Africa, Australia, and China, to North and South America. On our hillside in Los Angeles, we are fortunate to have a colony of California trapdoor spiders (Bothriocyrtum califonicum) a native Pacific Coast species. The heavy adobe soil poses a gardening challenge, but creates prime real estate for burrowing spiders. The native clay is structurally strong, while the hillside slope allows rapid runoff of water. This combination has prevented humans from planting exotic landscaping, which in turn has allowed these trapdoor spiders to thrive.

This photo shows the first trapdoor home I discovered in our yard. Though the spider camouflages its door with dirt and debris, the large size of this protective door allowed me to spot the distinctive “D”-shaped covering.

The back edge of the “D” creates the web-constructed hinge, which allows the spider to open it’s door when it detects prey on its doorstep. The spider lifts up the door, grabs the cricket, spider or other unwary arthropod, and pulls in down into its tunnel. Layers of webbing make the eight-inch deep tunnel a cozy home for the California trapdoor spider.

The door also provides protection. From inside, the trapdoor spider can hold the door tightly closed. The precision of the door’s closure makes it almost impossible to open without damaging the door. This was the first time I was able to open this door. Unfortunately, it was because the large adult female spider must have passed away. Female trapdoor spiders are believed to live up to 12 years. I have known this spider to reside in this large tunnel for 13 years.

Trapdoor females are homebodies, preferring to spend their lives in one location. Males may wander past her door, but the female spends her life quietly underground. She is also a good mother, raising her spiderlings in her web-lined tunnel. She protects them and provides them with food for a year until they are large enough to strike out on their own.

All around the hillside matriarch there are tunnels and doors of younger trapdoor spiders. Some are eaten by other predators and their tiny doors have broken off to reveal the narrow tunnel without an owner.

Others are approaching the size of their mother’s tunnel.

Spiders are ancient creatures. The fossil record shows evidence of spiders 350 million years ago, long before dinosaurs or the first mammals. How long has this colony of trapdoor spiders lived on this hillside? Probably, long before humans lived in this valley.

The experts don’t believe the shy and secretive trapdoor spider lives in the built-up city of Los Angeles anymore. But in little fragments of native habitat, these ancient creatures survive. I am in awe of this colony of spiders. I am careful not to plant too many plants on the bare earth they prefer. I knock on human neighbor’s doors when their overwatering threatens to flood the spiders. I try to preserve their plot of hillside so their colony can continue on long after I am gone.

Native wildlife is a treasure, a gift. Big or small, plant or animal, this year make it your mission to preserve and protect.

For great PICTURES of trapdoor spiders, including a mother with her young, visit

www.dbc.uci.edu/~pjbryant/biodiv/spiders/Bothriocyrtum%20californicum.htm