Spider expert Vikki Smith has invented a novel way of luring reclusive trapdoor spiders out of their long burrows – ‘beetling’. The standard technique that arachnologists use is vibrations from an electric toothbrush, but New Zealand Cantuaria trapdoor spiders are too clever to fall for that old trick - which is where Vikki’s secret spider attracting device comes into its own.
“I have this beetle,” says Vikki. “His name is Terrified Pete - and he’s a mealworm beetle. He wears a little harness and I walk him along in front of the trapdoor spider burrow. The spider is attracted by him because he’s prey and comes out. Oh, and the beetle usually gets away unscathed.”
The patter of tiny beetle feet and the small vibrations that the beetle sets off as it negotiates a minefield of silk strands radiating from beneath the camouflaged trapdoor are what alerts the resident spider to a passing meal. This sophisticated system of beetle detection is necessary as the spiders never leave their silk-lined burrows – they rely on their food walking to them. All the more remarkable is that female trapdoor spiders may reside in their burrow for up to 25 years – and never leave home once. For all that time they lie in wait, only erupting forth to grab an unwary insect and drag it down to devour in the privacy of their own ‘home’.
The only nocturnal visitor the female trapdoor spider doesn’t devour is the occasional passing male, out wandering in search of a mate. He’s presumably invited into the burrow for a spot of sex, before carrying on his way.
Trapdoor spiders live on mud or clay banks, and as the sons and daughters – when they eventually leave home after 6-18 months - set up residence right next to mum, a small area of bank can end up liberally honeycombed with tunnels that can be up to 30 cm long. The size of the trapdoor and the width of the tunnel are directly related to the size of the resident spider – over time, the growing spider excavates it to accommodate its expanding size.
Trapdoor spiders belong to a group of spiders known as mygalomorphs, which includes tunnel web spiders and tarantulas. Cantuaria spiders are endemic to New Zealand, and are the only New Zealand representatives of a family called Idiopidae, which has some Australian relatives. The taxonomy for the Cantuaria group is up in the air at the moment – spider expert Ray Forster described many species that Vikki and Canterbury Museum spider expert Cor Vink think are probably just one or two species. To do further taxonomy the pair require more male trapdoor spiders; during winter the smaller long-legged males leave their burrows to wander in search of females, so if anyone finds and collects one of these Cor would love to have it.
Vikki is studying trapdoor spiders as part of her PhD research, funded by scholarships from the Miss EL Hellaby Indigenous Grasslands Research Trust and the Mohamed bin Zayed Species Conservation Trust. She is using techniques such as a molecular clock to establish whether Cantuaria spiders have been in New Zealand since the break-up of Gondwana 65 million years ago, or whether they have dispersed here more recently, like most of New Zealand’s biota. Vikki says that their ‘homebody’ lifestyle makes it unlikely that they dispersed here, unlike many other spider species that have a ballooning life stage when they are young and can be blown long distances by wind. If her molecular techniques show that the spiders have been here a long time it will lend support to the idea that islands persisted during the Oligocene, about 25 million years ago, when much of what is now New Zealand was below sea level.