This paper is the first to describe the silk produced by Segestriidae spiders. Field and specimen data together with webs secreted by Namibian arid-adapted Ariadna spiders were collected from different research work stations. The silks were solubilized with hexafluoroisopropanol and characterized by Fourier transform infrared (FT-IR), matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) and differential scanning calorimetry (DSC) techniques, in order to get data on the silk composition. FT-IR analysis confirms that proteins are the main component of the extracted materials. MALDI-TOF mass spectra of silks of three different sites (R, M and K, with three varied environmental conditions: coastal foggy area, hot central desert area and savannah) reveal the presence of low-molecular-weight (< 10,000 g/mol) proteins mostly based on glycine and alanine amino acids. Besides many peptides with identical or similar composition, other low-molar mass proteins with different compositions were also revealed in these silks. The DSC curves show that the studied silks have different melting temperature ranges. This behaviour may be due to the proteins having different molecular weight and/or different amino acid composition. The presence of small peptides with different amino acid composition could be correlated to the different habitats where the spiders live. Hypotheses linking different amino acid compositions with environmental features are suggested. Keywords: Silk, Ariadna spiders, amino acids, Namibia, ecology.