The article is short so I recommend reading it. I started adding the key points below, but ended up including almost the entire article:

Number 16 (c. 1974 – 2016), also known as #16, was a wild female trapdoor spider (Gaius villosus, family Idiopidae) that lived in North Bungulla Reserve near Tammin, Western Australia. She lived an estimated 43 years and became the longest-lived spider on record, beating a 28-year-old tarantula who previously held the title. When Number 16 finally died in 2016, it was not of old age but from a parasitic wasp sting.

On March 1974, Australian arachnologist Barbara York Main began a long-term study of spider families. […] Main returned to the site annually, sometimes more frequently, for more than four decades.

Like other trapdoor spiders, Number 16 spent her entire life in the same burrow, subsisting off the edible insects that walked on her burrow’s trapdoor-like silk roof.

For her 40th birthday, research assistant Leanda Mason wanted to give the spider a mealworm, but Main denied the request since it would interfere with the study

Because of Number 16, Main’s project took far longer than she had expected. She continued to work into her late 80s, but she “began to look forward to the project’s end,” The Washington Post reported. Finally, when Main’s own health declined before the spider’s, she passed the project on to Leanda Mason.

On 31 October 2016, researcher Leanda Mason discovered Number 16’s burrow in disrepair. The spider was gone. Evidence suggested she was killed by a parasitic spider wasp

“She was cut down in her prime […] It took a while to sink in, to be honest," said Mason

After retiring, Barbara York Main moved to a care facility for Alzheimer’s. Leanda Mason, who kept in contact with her mentor, said in 2018 that Barbara “remembers No. 16” but “forgets that she’s died.”