Number 16 (c. 1973 – 2016), also known as #16, ^[1] was a wild female trapdoor spider ( Gaius villosus, family Idiopidae) that lived in North Bungulla Reserve near Tammin, Western Australia. She died in 2016, at an estimated age of 43 years, and is the longest-lived spider recorded to date. ^[1] Number 16 did not die of old age, but was most likely killed by a parasitic wasp sting. ^[2]

Long-term monitoring

Number 16 was studied in the wild by arachnologist Barbara York Main from March 1974 until 2016. ^{[1] [A]} She was part of the first cohort of dispersing spiderlings to establish a burrow at the study site, and her burrow was the 16th to be marked with a peg. ^[1] By 1978, Main had tagged 101 burrows at the study site, within a few metres of each other. ^[4]

Number 16 spent her entire life in the same burrow, which is typical for her species. ^[2] For over 40 years, her status was monitored by Main and her collaborators either six-monthly or annually. ^[1] As Number 16 became older, the researchers developed a tradition of always checking her burrow first when they visited the site. ^[4]

Death

On 31 October 2016, researcher Leanda Mason discovered Number 16's burrow in disrepair, and the spider missing. ^[4] The silk plug of her burrow had been pierced by a parasitic spider wasp, suggesting that she had been parasitised, either before or after death. ^[1] During a survey six months earlier, Number 16 had been alive. ^[1] “She was cut down in her prime [...] It took a while to sink in, to be honest," said Mason. ^[4] The spider's death received widespread publicity in late April 2018, with the publication of a research article in the journal Pacific Conservation Biology. ^[1] Based on the burrow fidelity of females of her species, the researchers concluded with a "high level of certainty" that Number 16 was 43 years old at the time of her death. ^[1]

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