A web of mystery: In search of the lost Fagilde’s Trapdoor Spider

Sérgio Henriques dreams about spiders. He dreams about trekking through forests looking for them. He dreams about the patterns in the forest that reveal the animals’ whereabouts. He dreams about the way they move, the way they think, how they defend themselves from invaders.

Mostly, though, he dreams about saving spiders from extinction—and most recently one spider in particular: the tapdancing Fagilde’s Trapdoor Spider, one of Re:wild’s top 25 most wanted lost species. Before he can protect the spider, however, he has to find the elusive animal, which has not been scientifically documented since it was described in 1931 in Portugal.

“It takes a lot of time to look for signs of this species,” says Henriques, who is the invertebrate conservation coordinator at the Global Center for Species Survival at the Indianapolis Zoo and co-chair of the IUCN SSC Spider and Scorpion Specialist Group. “Some lost species that are bigger and don’t live underground might be easier to stumble across, but this is not one of them. This is too cryptic; it hides too well. You have to be very intentionally looking for it in a specialized kind of way.”

So Henriques does, as often as he can. Native to Portugal, but most recently an Indianapolis resident, Henriques has been spending time in his home country visiting Fagilde, a small village in north-central Portugal where the spider was originally found. He is the last on his team to go to sleep and the first to get out into the field. His steadfast efforts, and a lasting love for spiders that rivals in strength the fear arachnophobes feel, has led to what possibly—very possibly—may be the rediscovery of a spider lost to science since Herbert Hoover was president of the United States.

Arachnid amor

Trapdoor spiders are found in Europe, the United States, South Africa and Australia. Unlike the elaborate webs we associate with most spiders, trapdoor spiders have their own unique method for both hunting and defense. They dig a nearly perfectly cylindrical hole in the ground—so perfect that it is hard to believe it wasn’t done with a human tool—that is the entrance to a burrow. These burrows are usually no more than 4 inches deep and 1 inch in diameter. They then use leaf litter and soil to build a camouflaged door to block the burrow entrance.

The door comes with a locking mechanism—little holes that the spider can use to pull the door closed. When the spider feels vibrations over the burrow, it can determine whether it is a predator or if it is dinner knocking at the door. Scratching vibrations indicate that a predator, like a wasp, may be snooping around, and the spider can lock the door. When the spider feels smaller vibrations, like, say, those of a small beetle, it can swing the door open and bon appetit. Female spiders live in the same burrow for years, often decades, raising their young here before they go off to build their own homes, often nearby as part of a spider “town,” Henriques says.

Males, on the other hand, will venture out when they are ready for breeding, an opportunity for trapdoor spiders to show off their adorable (yes…an adorable spider!) charm offensive. A male will find a burrow door and drum at it with his legs, essentially “singing” to the female in his own way. Entomologists suspect that each species has its own song, which matches the musical tastes of the species’ females.

While every other known species in the Nemesia family builds their burrows perpendicular to the ground, Fagilde’s Trapdoor Spider builds their tunnels horizontal to the ground. Not much else is known about the species. It was discovered and described by the pioneering female entomologist, Amelia Bacelar, which in and of itself was unusual for that time. She was only able to research female spiders of the species, which wound up in a Portugal museum that burned down in 1978, and the only evidence of the spider’s existence with it. No biologist has ever seen a male of the species. All that exists today is a possible illustration of the spider’s genitals and lots of questions about the spider’s behavior, ecology, threats to its survival, and whether it even still exists.

Henriques is trying to change that.

Spidey sense

At the end of 2021, Henriques set off to try to find the species with a team of three others, Luis Crespo, Mykola Rasko and Pedro Sousa. They based their search in part on interviews they had conducted with Fagilde about whether they had seen anything like the spider, including in their own homes or pool drains.

“When talking to landowners, there’s usually a bit of awkwardness at first because they often think it’s very weird. But after getting to know me for five minutes, hearing me talk about the spider, they decide it makes complete sense and they’re curious. They often have lots of questions about insects. And sad stories about the things that they used to see as young children and no longer see.”

After the interviews, the team used satellite data to look for fragments of forest close to where the spider was originally recorded in the 1930s. After validating that data, the team set out artificial shelters—some made of stone and others of wood—in hopes that wandering males would use the shelters to hide when taking a break in their quest for a tryst. And then the search began—flipping rocks and logs, turning over the artificial habitats (which included a phone number for curious individuals who might stumble upon them) and, most importantly, examining the forest floor for the telltale-yet-clandestine trapdoor.

“It’s impossible to explain, but even when you remove the moss and leaf litter from the top of a trapdoor, you see nothing,” Henriques says. “There is nothing to be seen. The lid is exactly the same materials and the exact same color as the ground. It’s just me on the ground on my knees, looking at the floor with all the patience in the world, just looking at it very hard and trying to see something circular in the ground. That’s all we can do. Just look at it. We look for patterns. For each trapdoor I find, I find a thousand fake trapdoors.”

This time, however, Luis Crespo, a member of Henriques’ team, found a promising trapdoor—the door was locked, which meant someone was likely at home. Henriques very carefully dug a hole into the burrow to find a mama spider and about 10 of her babies. Because it was impossible to tell on sight if this was the lost Fagilde’s Trapdoor Spider, the team carefully removed part of one of the spider’s legs, which the spider can release like a lizard releases its tail when threatened. The spider then closes up the wound and will regrow the leg. With the mystery of whether there was a trapdoor spider species in this area solved, the team now had an even more challenging question: Is this the lost Fagilde’s Trapdoor Spider?

Lost and found-ish

Sometimes lost species rediscoveries are straightforward. The species has a telltale physical marker and can be verified by camera trap, or DNA collected non-invasively matches the DNA of an individual saved in a museum. In the case of Fagilde’s Trapdoor Spider, the best that the researchers can do with the DNA from the leg is compare it to the DNA of other trapdoor spiders in the area. If it matches the DNA of a known species, it means that Fagilde’s Trapdoor Spider is actually the original name of a relatively more common species that is found elsewhere in Portugal and maybe even parts of Spain. If it is not, Henriques says that it is reasonable to deduce that this is a distinct long-lost species with a very narrow range.

“Nothing else resembles this species, and no evidence suggests that there’s more than one species of trapdoor in the area,” Henriques says. “This would be, to the best of our knowledge—to the best of anyone’s knowledge—a rediscovery.”

Either way, Henriques is going to continue collecting information. He is working with school children and local landowners to educate them about the species and take photos of spiders as they see them to send to him. He is also interested in learning more about the threats to the trapdoor spider, which include forest fires that are burning hotter as the climate changes, flooding as the result of dam construction nearby, and infrastructure development. Given that trapdoor spiders live in such small areas, any one of these could mean extinction.

“If it still exists in a particular habitat, that means that whatever is happening there, it’s what we should be doing more of,” Henriques says. “If we find the species in certain places and understand how that place has sustained it, we can take that information to the local government and local stakeholders to work together to protect it so that we don’t lose it again.”

The DNA results are expected in the coming months, so check back on re: the wild and our social media channels (Facebook, Twitter, Instagram) for updates.