March 14 was International Save a Spider Day, and this year, we’ve taken a closer look at an iconic group of New Zealand spiders – the tunnelwebs. Not only were these spiders the inspiration for the design of Shelob in Peter Jackson’s Return of the King, but their family is also unique to Aotearoa New Zealand. After the black tunnelweb spider (Porrhothele antipodiana) came 11th in this year’s Bug of the Year contest, Curator of Invertebrates Phil Sirvid and PhD student Shaun Thompson think they deserve a bit more love.
The black tunnelweb: at home around our homes
Tunnelweb spiders (genus Porrhothele) will be familiar to many, as one species, the black tunnelweb, is a common sight. It has adapted to human-modified habitats and is at home in gardens as well as native forests. Most other Porrhothele species are confined to relatively small areas, but, perhaps because of its adaptability, the black tunnelweb is quite widespread (Auckland to Dunedin) and has even been introduced to Rēhoku Chatham Island from mainland Aotearoa. A black tunnelweb might build its dense, white web in your woodpile, a damp corner in the garage, or in a discarded flowerpot.
In the spring, you might even see a lovelorn male that has wandered indoors by accident as he tries to find a female of his own kind to mate with. More likely, you’ll find his dried-up corpse with his legs tucked under his body, his quest to find a mate unfulfilled. Truly love’s labour lost! These spiders can live several years but require humid conditions to thrive. Our homes are usually too dry for them to survive for long.
Gentle lovers and snail eaters
As it is so ubiquitous, the black tunnelweb is the best studied member of this genus. A study of courtship in this species shows it is comparatively gentle by spider standards. If the male is allowed to get close enough to embrace the female with his specially modified legs, it’s like she melts in his arms (OK, legs!) and she quietens, showing no desire to eat him at all! These spiders are also known to attack and eat the introduced garden snail (Cornu aspersum) and have even been known to take out mice, although it’s usually the other way round.
A special spider family
While New Zealand has many spider species that are only found here (some 95% of over 1100 species so far), spider families are another story. Currently, we only have two, and Porrhothelidae, home to the genus Porrhothele, is one of them. One study using molecular data suggests this family diverged from its nearest relatives around 187 million years ago. Back then, Aotearoa was still firmly attached to the supercontinent of Gondwana. If members of the family once existed in the other lands that came to be after the breakup of Gondwana, they do not appear to have survived to the present day.
But wait, there’s more!
Until recently, there were only five species in the genus, but we recently added a sixth species, Porrhothele peninsularis, which is only found on Te Pātaka o Rākaihautū Bank’s Peninsula. This was the first tunnelweb spider to be described since 1968.
And that’s just a start. We know there are more than six species of Porrhothele in New Zealand, and we are in the process of naming and describing them. Most of these new species are unusually small, with adult males no more than 10 mm long, about half the size of male black tunnelweb. They are often found in the same areas as larger species, with some showing a preference for living in trees. There is also at least one new regular-sized tunnelweb, and for the first time, we’ll be able to show people what the Te Tai Tokerau Northland tunnelweb (P. quadrigyna) male looks like.
