Observations of Pterinochilus chordatus (Gerstäcker, 1873) in Tanzania

Guy Tansley

During January 2018, I travelled with Richard Gallon, Paul Carpenter, Mark Carpenter and Ralf Konen to north eastern Tanzania for a two week research trip. Our main aim was to document Pelinobius muticus Karsch, 1885 in its natural habitat (which we achieved, article in prep.) but we also found and photographed four other Theraphosidae species: Heterothele villosella Strand, 1907, Eucratoscelus constrictus (Gerstäcker, 1873), Pterinochilus murinus Pocock, 1897 and Pterinochilus chordatus (Gerstäcker, 1873).

Pterinochilus chordatus is an old-world tarantula (or ‘baboon spider’), first described in 1873 by Carl Eduard Adolph Gerstäcker. This species occurs on the east side of the African continent, from south Sudan in the north, to Tanzania in the south. It has a body length of up to 50mm and a leg span of up to 150mm. Overall colouration of specimens in this region is a mix of grey, olive green, brown and yellow with a symmetrically spotted and striped abdomen. The legs are banded with pale yellow and the carapace has the typical Pterinochilus spp. starburst pattern although less obvious than in P. murinus. Colour is variable depending on age and stage in the moult cycle as can be seen in sub-adult specimens.

In north eastern Tanzania, P. chordatus inhabits acacia scrub forest and is an obligate burrowing species. Observed burrows were shallow (approx. 240mm deep and 190mm in length), silk-lined and curved slightly (approx. 68 degrees) with a small chamber at the end. Burrows are typically built amongst grass and this is often incorporated around the entrance. Burrows entrances are usually silked over during the day and measure approx. 40mm in diameter.

The climate in this part of Tanzania is variable with a distinct rainy season lasting several months. It was overcast during our stay and heavy downpours were common, resulting in the environment changing dramatically, sometimes overnight. Observations showed that P. chordatus habitat is subject to flash floods but they have evolved in such conditions and not only survive, but thrive here.

Approaching one burrow, we observed an adult female sitting at its burrow entrance around mid-morning, in dappled sunlight from the surrounding trees. Tarantulas are known to bask in sunlight but there was something strange about this particular spider. Instead of being stretched out to expose as much of its body to the suns warmth, this spider sat with most of legs curled under its body.

Initial thoughts were that the spider was in some distress as a dead or dying tarantula is often found with its legs curled underneath its body (often referred to as the ‘death curl’). However, when disturbed, the spider quickly retreated to the safety of its burrow and was apparently fine. Sitting quietly nearby, we watched as the spider eventually re-emerged and again, took up this uncharacteristic position at the burrow entrance. Slightly puzzled by this, it wasn’t until after finding another adult nearby that may help us explain this unusual behaviour.

This next female P. chordatus was covered in mites, was missing both palps, one foreleg and had two re-gown legs.

It wasn’t until later that we made the connection between this spider and the unusual basking behaviour in the previous spider. It’s likely that a predator is attacking these spiders while they’re out basking or waiting for passing prey at their burrow entrance.

Unfortunately, we can only speculate as to what this predator might be. Large Pepsis sp. wasps were observed throughout their habitat and are a known predator of tarantulas but they don’t remove legs, preferring to keep the spider in one piece for food for their grubs. Other candidates include scorpions (large Pandinoides sp. are found in the area), small cats such as the Serval (Leptailurus serval) and of course, countless bird species but further research is required to properly identify the culprit.

It is assumed that the spider demonstrating the unusual basking position was adapting its behaviour in response to a predator. Had this spider previously been attacked and re-grown lost appendages in the past? Sadly we will never know for sure but nevertheless, it was fascinating to observe these spiders and their behaviour in their natural habitat.

This article first appeared in the Journal of the British Tarantula Society, 34 (1): 7-12 (2019).