The Ariadna Spider ( Araneae: Segestriidae )

By Prof. Erminia Conti, University of Catania

With this article Eagles Rock Tours introduces its Conservation Journal. Under this topic, we will publish a series of popular scientific blogs by various authors, starting with Prof Erminia Conti and Prof Giovanni Costa from the University of Catania, who for 20 years did research in the Namib Desert and discovered many exciting phenomena.

Namibia, land of contrast, is undoubtedly one of the most enchanting country in the Southern Africa.

Endemic plants like Welwitschia mirabilis and Aloe dichotoma in the South, together with the big five (elephants, rhinos, leopards, lions and buffalos) make this region unique in the African scenery.

In spite of these large animals, however, a myriad of fascinating but often not visible animals inhabit Namibia and especially its ancient desert.

As a matter of fact, the Central Namib is one of the most fascinating environment on earth, as it is the oldest desert worldwide.

During different missions, we discovered populations of Ariadna spider in diverse gravel areas of the Namib Desert. Of our research stations, four (G, M, R, W) were within the Desert biome and one (K) in the Savanna biome (see figure). These small nocturnal and sit-and-wait predatory spiders excavate nearly vertical cylindrical burrows. These burrows are inhabited by sedentary females and are thickly lined with silk having site-specific chemical properties. All burrows are radially surrounded by a stone ring of mostly small quartz pebbles at the burrow edge that amplify the vibration of moving preys such as ants. Spiders spend the whole night to construct the burrow (see film).

This so stressful environment compelled animals to find adaptive strategy to survival. As such, the burrows of our little spiders have different depth according to the surface temperature. The higher is the soil temperature, the deeper is the burrow. This, in turn, means that the silk is different for different locations: the burrow deeper are lined with a silk stronger than other ones.

Moreover, Namibia is very rich in natural resources such as ore deposits of copper, zinc, gold, tin, lead, uranium and other heavy elements. Therefore, an intense mining industry has been long developed over the past 50 years in the territory of Namibia, including the Namib Desert and large parks and protected areas (e.g., Dorob and Namib Naukluft coastal parks). There is, therefore, a potential impact associated with mining activities in terms of ecological processes in super arid areas like the Namib Desert. Despite their very small dimensions, these spider showed a great ability to accumulate heavy elements regardless the specific habitat features. This so confirms the value of these spiders as bioindicator of heavy elements in the Central Namib Desert and their importance for conservation purposes.