Trapdoor spiders at Mokoya Lodge: exciting new finds

Ian Engelbrecht
Invertebrate Scientist
Nature Conservation
Gauteng Department of Agriculture and Rural Development

On Saturday the 25th of April, 2009, Nic McLean of Mokoya Lodge phoned me to say that they had just had rain, and my heart jumped. I had just started a project to discover and describe the trapdoor spiders of Gauteng Province, and my research had shown that rainfall was the key factor to finding them.  That Monday I headed out to the Lodge with my field team and we started installing pitfall traps.  When we checked the traps the next morning we found our target, a new species of cork-lid trapdoor spider in the genus Stasimopus.

Trapdoor spiders are fascinating animals.  Females spend most of their lives in self-made tubular burrows in the soil. The burrow entrance is covered with a lid which is camouflaged against the surrounding soil surface.  At night they sit at the top of the burrow with the lid very slightly lifted, waiting for unsuspecting insects to come within striking distance. They don’t see very well and rely on vibrations transported through the soil to tell them if prey is nearby. At lightening speed they pounce and drag the helpless victim back into the burrow to be consumed.  Life in the confined burrow has produced some remarkable adaptations in these spiders.  They have very stocky bodies and short thick legs for moving up and down and rotating rapidly within it. They are so well adapted to living in a tube that they are very clumsy and awkward if removed from it. Males are equally remarkable. As youngsters they look and behave just like females, but undergo a complete transformation when they reach maturity.  Their legs become long and thin, better suited for walking, and they develop sperm bulbs on their pedipalps (leg like structures next to the mouthparts) and several modifications on their front legs.  These are all adaptations for searching for and mating with females.  After rainfall, males leave their burrows in search of females to mate with, and this provides the opportunity to collect them for scientific research.

As a result of the secretive habits of trapdoor spiders we know very little about them.  We know so little that we often don’t know what species we are looking at. What we do know is that they live for many years, that they only reproduce once a year and that they have few offspring.  These are the characteristics of species of conservation importance, and make the trapdoor spiders a priority for research aimed at finding out which species need to be protected. My project aims to do this by sampling the full extent of Gauteng and its natural habitats looking for species with specific habitat requirements and limited distribution ranges. Where these species occur in areas of high urban development and agricultural activity we can take the necessary measures to protect them from any further habitat destruction.

So why the special interest in the spiders at Mokoya Lodge?  When Nic and I were enthusiastic youngsters with an early interest in spiders and other such creatures, we met Martin Filmer, then chairman of the Spider Club of Southern Africa. He had discovered a bizarre trapdoor spider in the Hekpoort area.  It had a large horn in the middle of its head, a feature not known in any other trapdoor spider from anywhere in the world.  He had accidentally lost the specimen before it could be named. He mounted several expeditions to the Hekpoort area since to try and locate more specimens, without success.  When I started my project I knew that this species was a priority to locate, and that Mokoya Lodge would be a good place to start. And these were the spiders we found on that day in April.  We got a total of four trapdoor spider species at Mokoya Lodge, and several others in the surrounding area.  These discoveries have contributed important information to our knowledge of these spiders in Gauteng, but we still have a long way to go to get a complete picture.  I will be returning to the Magalies River valley and the Hartebeesfontein Conservancy in the future and I’m sure many more interesting discoveries await.