Let's talk about... trapdoor spiders!
There are thousands of species of spiders on planet Earth. 45,000-50,000 is a conservative estimate for species diversity, and they can be found in virtually every conceivable environment on every continent except Antarctica. There are spiders that build massive webs in the canopies of rainforests, spiders that construct intricate silken tunnels from which to strike, spiders that create almost invisible envelopes to hide within under leaves, spiders that swim, spiders that skate on water, spiders that hunt tirelessly and run with such incredible bursts of speed they can move 40 times their body length in a second. But one group that seems to always maintain a level of popularity in the hobby are the trapdoor Mygalomorphs and Mesothelae spiders. They construct silken burrows, put a little hinged lid on top, and then spend years being as motionless as possible and living in a tiny little chunk of real estate. These are the trapdoor spiders, and this is their story.
We don't know exactly when it was that a burrowing spider evolved the methodology of creating a small lid. Many Theraphosidae (tarantulas and relatives of the Mygalomorph trapdoors) spiders are burrowing organisms. They dig large intricate burrows deep into the soil. Many of them wait patiently for prey to move within striking range, and all of them benefit from predator avoidance by staying concealed in the dirt. One genus, Idiothele, takes it a step further. This is a small baboon spider from central Africa that build burrows and frequently create clumsy little lids for them. While not as well constructed as true trapdoors, it does perform a similar function.
The fossil record does give us some examples to reference, Megamonodontium mccluskyi lived in Australia's forests some 11-16 million years ago. This extinct genus belongs to family Barychelidae, commonly called 'brush footed trapdoor spiders', and its relatives still live throughout Australia and Indonesia.
We also know that trap doors in family Ctenzidae have natural ranges throughout the Mediterranean as well as North and Central America. Phylogenetic analysis of genus Ummidia in North America and the Mediterranean show a very close relation and shared ancestor, so this tells us that prior to the breaking of Laurasia (66-30 MYA) and the Atlantic divide forming, there were trapdoor spiders. It is very likely that these successful spiders developed this behavior very early in their evolutionary history, and it continued to serve them well. Mesothelae spiders exist in the fossil record, dating back 300 million years, and while we can't be sure these ancient ancestors built trap doors the way modern types do, it's not a terrible stretch to imagine it.
Regardless of where they live and who they are related to, all trap doors have similar survival strategies. Both sexes create burrows, line them with silk, build a small flat, hinged lid, and some types may add on a series of trip lines, vibration detectors, or a small 'door mat' of woven silk. These extensions help the spider detect movement of prey, or potential predators, without having to expose themselves to risk. Females will remain in these burrows their entire life. Unless some disruption, such as flooding, predator excavation, or man made construction, cause them to evacuate. The males, however, are forced to be a bit more adventurous. Upon maturity, they venture out of the burrows that have been their entire life for the single most dangerous foray of their lives. Reproductive attempts. They are fully exposed while searching for receptive females, and many are snatched up by predators long before they fulfill that biological prerogative. Not dissuaded by this invariable litany of hazards, they charge forth into a world that is inconceivably larger than their tiny burrows, and the few that are lucky enough to pair with a female pass those genes on to the next generation of little trapdoors. Many female trapdoors live long lives, estimates for longevity are quite broad but decades are not unheard of. A trapdoor spider living in Western Australia was part of a longevity study started in 1974, and she survived for 43 years, before falling prey to a wasp.
These spiders are fascinating organisms to keep but can be frustrating for some hobbyists and keepers. Unless your specimen happens to build its burrow close to the sides of the habitat, you are often left with a container of soil, a trap door lid that may or may not be visible, and occasionally insects disappear in the habitat. There is no incentive for females to vacate their burrows, and these spiders survive by being incredibly patient sedentary predators. Despite these aspects, these wonderful Arachnids continue to maintain popularity, and my own shelves have several containers of dirt that occasionally needs feeding.
Mature female Ummidia sp. from North Carolina
Mature female Liphistius sp. 'Suwat' from Java, Indonesia
Mature female Bothriocyrtum californicum from Southern CA.
Liphistius burrow open
Liphistius burrow closed, demonstrating trip lines and clustered debris to conceal lid.
Hope this article was informative and the photos are all images of trapdoor species I maintain in my own collection.