Trapdoor Spider

The spider digs a burrow, typically a few centimetres wide and up to around 30 centimetres deep, lines the walls with silk to keep them from collapsing, and builds a lid over the entrance from alternating layers of soil and silk, attached along one side by a thick silk hinge so it swings like a door. Many species disguise the outside of the lid with moss, dead leaves, or soil to match the surroundings exactly. The spider sits just below the closed door during the day and, at night, holds it open a crack with its fangs or front legs while resting the tips of some legs on the door or on silk trip lines spread around the entrance. When it feels the vibrations of an insect walking nearby, it flings the door open, lunges out, seizes the prey, and drags it back inside, closing the door behind it, all in well under a second.

Trapdoor spiders, especially females, are among the longest-lived spiders known. Females are extremely sedentary and may occupy and gradually enlarge the same burrow for their entire adult lives, and because they grow slowly, reproduce over many years, and face few predators once safely underground, individuals can survive for decades. The best-documented case is an Australian trapdoor spider studied in the wild and nicknamed Number 16, which was monitored in the same burrow from 1974 until 2016, an age of 43 years, when she died after her burrow was fatally damaged by a parasitic wasp, making her the oldest spider ever recorded.

Most trapdoor spiders are not considered dangerous to people. They are shy, spend almost all their time underground, and bite only if directly handled or trapped against skin, and the bites of the great majority of species cause no more than localised pain and swelling similar to a bee sting. A few unrelated burrowing mygalomorph spiders that are sometimes loosely called trapdoor spiders, such as certain Australian funnel-web relatives, do have medically significant venom, but the true trapdoor spiders in families like Ctenizidae are generally harmless, and their fascinating lifestyle is far more notable than any threat they pose.

While trapdoor spiders as a whole are widespread and many species are common, the group includes numerous species with very small geographic ranges, sometimes restricted to a single hillside or patch of soil, and these narrow-range species are highly vulnerable to habitat loss. Because females rarely move far from their birth burrow and dispersal is limited, populations recover very slowly, and once an area of suitable, undisturbed ground is cleared for agriculture, housing, or mining, the local trapdoor spiders are usually lost and do not return. Several such species, particularly in Australia and South Africa, are now recognised as threatened.