Due to the economic importance of Acacia tortilis trees in the desert ecosystem, a study was made concerning these trees in wadi Mandar, Saint Catherine Protectorate, South Sinai, Egypt. Thus, abundance and diversity of major insects and araneids species were searched. Collection was achieved by using pitfall traps technique in the trees area. Results indicate a total of 19467 individual insects and araneids. They belong to 68 species of which 58 species were identified. The collected species were included in 37 families belonging to 13 orders. The most abundant insect species was Monomoriun niolticum (O. Hymenoptera, F. Formicidae). On the other hand, the most abundant araneid species was Stegodyphus dufori (F. Eresidae). Separated curves for each insect and araneid order were constructed to determine the most abundant species in each order. Species diversity pattern of Acacia insects and araneids for the tree types was determined and the same was made among months of the study period. A detailed discussion was made to elucidate results of this research in relation to other authors.