Research on the biotope of Heterothele gabonensis in the national park of Lope.
By Cédrik Grenier
After a preparation of more than two years for my expedition in Central Africa, I finally took the decision to go to Gabon, from January fourteen to February fourteen. My choice seemed to be the best considering the circumstances, because several points made this expedition interesting for me who for more than six years have been impassioned and specialized in the African species.
The species found in Gabon were unknown and, at this point, few people had made serious research in this country so far, which made it even more interesting. However, this fact complicated the expedition because I did not have any benchmark. How should I begin my research?
I studied the country for some time, trying to visualize where my research could be most profitable. The heart of the country really attracted me for its drier climate, the scarcity of its savannas, the mountains furnished with forests passing from released and dry to dense and wet. The faunal reserve of Lope, in Gabon, thus seemed to be the ideal choice to begin my research. Having in hand my permit of research, I thus started by exploring the galleries surrounding the small village where I lived; the village of Lope.
With two days of forced rest, caused by a wound in a knee, my first week of research was very difficult since no tarantula, nor even a trace was found. Only the sixth day of research has enabled to me to unearth the first one. Considering the fact that this species has an average size of two centimetres, this female Heterothele gabonensis, which measured nearly 2.5 cm, was of a relative good size. As for the mature males, four were examined and also had 2.5 centimetres body length.
As of this day, I realized that within the interior of my territory of research, I would find this species in only one type of environment. This specific environment must fulfill several precise conditions to be advantageous. Indeed, if I withdrew only one of these conditions, I would not find any individual. So if all the elements were joined together, it would be possible to find several specimens in only one day. Only one exception to this was a group found at 6 meters high in a palm trees in the middle of the savannah, which contradicts all my observation made in my research.
The respective elements of this biotope are a relatively dry and clear environment, usually met in open forest. I easily met these conditions in the galleries surrounding the village. Here is where this story becomes more and more interesting.
The majority of the retreats were discovered near water, where a strange tree called Uapaca, can be found in good numbers. I tried to understand why, and after a few weeks of observation I realised, that what they were looking for was not the water but the trees itself, and that this tree grows near water.
Their choice for this tree did not surprise me, since it is definitively the one that offers the greatest number of relatively safe retreats in this type of environment. Cavities which can reach up to forty-five centimetres, are formed inside many air roots going up to four meters height, thus classifying this species as being arboreal for this sector. The small door giving access inside was blocked most of the time by silk, thus blocking the entry for the undesirable intruders. A striking fact; the majority of the nests of termites given up at the base of some trees were used by small groups. These nests of termites are not solely on Uapaca, and by the way it is the only place where I found some which did not reside in the Uapaca. On more than seventy retreats, the temperature inside was of 25.5 degrees Celsius, for a humidity estimated at 85%. It’s impossible to say for the moment if this species is only arboreal, since research was made on a limited territory of approximately twenty kilometres, however in various biotopes. It should be noted also that in several retreats, old exuvium passing by spiderling to adult were found, proving thus that they passed there a good part of their evolution.
Many groups, small or more important, were observed, living on the same tree. However no retreat revealed more than one mature spider, thus classifying them more tolerant than favourable for the community. These groups of two to twenty individuals count male mature, female mature with or without egg sac, juvenile and spiderling.
During the third week of the expedition, I met my first on a total of four mature males. This fact did not surprise me, since I had seen females which seemed to be pregnant, considering the size of their abdomen. Some specimens carried an egg bag while others lived in the middle of spiderling, the sac being thus already open. When I saw these ones, I realized that this period of mating must have been around two month ago, in fact at the beginning of November.
Various egg sacs were withdrawn from the nest after the spiderling hatched in order to count the number of exuvium inside. Here results: thirty-three for the first bag, thirty-nine for the second and twenty-seven for the third.
I was really surprised to note that all the specimens observed had small abdomens, in spite of a superabundance of good food for this species. Despite everything, some pieces of food could be collected in order to try identification. Very few crickets, some bodies of large consumed ants were finally found, which lead me to believe that they were defending against them rather than to eat them. I found it very strange that few pieces were found, and finally, I found the answer which, I have to say, was not part of my assumptions. What at first sight seemed to be some attacks of small black ants finally was something that totally shocked me. Indeed, after long observations I realized, that those ants did not attack the tarantula, but simply do the housework by removing exuviae and remains of food from their retreats. This explained why very few pieces of food were found, which is extremely interesting. What a team work!
Even if the result of the work of the ants explained why no pieces of food are found, it did not explain why they were poorly nourished. The list of predators is short, but the existing ones are found in very large numbers. Indeed, you surely will have guessed it, not all ants have the kindness to do the housework without demanding a return! Three species, even aggressive towards humans, literally devastate the forests which I explored. In nearly 25% of the seventy studied retreats, one species in particular, unknown even by guards, is of red color with a black head, approximately two centimetres long, was discovered in the same tree. I was very surprised that these ants used a nest of Heterothele gabonensis to install their colony. The legionary’s ants of the Dorylus family, also called Magnan, also make devastations because an attack covers a large territory and because they are always moving. The probable assumption concerning the fact that the tarantulas are not nourished very well is undoubtedly that there are too many ants and that they remain hidden as long as that is possible.
In conclusion on this species, more than seventy easily recognizable nests, with or without specimens inside, could be observed and studied. Thus, the results of this research certify with accuracy the information collected for the sector of Lope. I want to thank the CENAREST for their collaboration, Richard Gallon for the identification of the specimen, Marylyn Dufresne for helping me to write the article as well as Rick West for its very useful information that helped me all along the travel.