OCTOBER 2020
Our speaker, Dr Leanda Mason of Curtin University, is, in her own words “Advocate for the Conservation of Non-charismatic Species”. She completed her PhD on the urban ecology of trapdoor spiders and their kin, to better understand how we might conserve them for future generations. Her thesis was titled “Living on burrowed time: mygalomorph spiders of Perth city”.
Trapdoor spiders have a very low metabolic rate, do not eat very much, can close their lung-books, and live very long lives. They live in web-lined burrows, usually over 20 cm deep, with an extremely well-camouflaged lid. Silk or twigs are attached to the rim of the burrow, and these spread out like trap lines in the form of a silk doily, allowing these spiders to feel vibrations and sense when prey is near their burrows.
Gaius villosus burrow
Image: L Mason
Males have longer legs than the females and leave their burrows when sexually mature to search for a mate, mostly in the wetter months, and are attracted by pheromones in the female’s doily web. A male will ejaculate onto a silk mat before filling his palps, grappling with the female and transferring sperm to her using his palps. The female lays her eggs in the burrow and looks after her brood for nine months. When spiderlings leave their mother’s burrow, they will build their own burrows fairly close to their mother’s, enlarging their burrows as they grow.
G.villosus female
Image: L Mason
Trapdoor spiders evolved when global conditions were more humid, and it is possible that burrowing was an adaptive response to a drying climate, because humidity is retained in the burrow.
Leanda was inspired by the “spider lady”, Barbara York Main, and her love of mygalomorphs was kindled. Barbara supervised her Honours and PhD work, and has been her highly respected mentor ever since. Barbara, who died last year, was a Co-Patron of our Club from 1999, and a fellow Club naturalist with her husband, Bert Main, as well as Harry Butler, Dom Serventy, Rica Erickson, John Dell and other prominent members. She published six articles on spiders in our Club’s journal over the years. Altogether, Barbara published 4 books and 90 papers and described 34 new species and 7 new genera. She was awarded the Order of Australia in 2011 and the Royal Society of WA medal in 2018. David Attenborough produced a television film on Barbara and her work in 1981 called The Lady of the Spiders. For 40 years, Barbara monitored the site of the famous “Number 16” – the oldest known spider in the world that has been monitored scientifically, which reached the grand old age of 43.
Barbara York Main (1980’s) at North Bungulla
Image: Ron York
Leanda was bequeathed the monitoring of #16 when Barbara retired. Trapdoor spiders are short-term endemics, having poor mobility, a slow rate of dispersal and a low reproductive rate. They are specialists, and cannot re-locate or re-colonise. Leanda’s PhD survey comprises 136 quadrats in 41 patches of land throughout the Perth metropolitan area. She has found that rabbit digging disturbs the spiders and that Veldt Grass has a big impact on them. Different species of trapdoor choose different habitats to burrow in, and some preferred to make burrows in Veldt Grass areas even though it was detrimental to them. In the small areas of bush left in urban areas, the populations have a low chance of recovery after fire. If the lid is destroyed, the spiders are vulnerable to predation by ants or wasps. Weeds invade after fire, and there is a high loss of biodiversity and high rate of extinction. Now having finished her PhD work looking at the effect of fire and urbanisation on the survival of trapdoor spiders, Leanda would like to establish a captive breeding program for these endangered spiders.
Trapdoor spider burrows are very difficult to locate in the bush, but Leanda said that a good observer can develop the skill of recognizing the pattern of radiating sticks surrounding the lid. A trapdoor spider can be monitored through the Bookend Trust, which has made a film called Sixteen Legs.
Mike Gregson