Kin selection theory predicts that cooperation should evolve among kin to reduce the costs of helping and the incentive to cheat. Altruistic behaviour provides individuals with either direct or indirect fitness benefits. As a necessary prerequisite, individuals need to recognise kin to direct their help towards them. Thus, kin recognition is a key feature of many social animals. Ultimate benefits of altruism are well studied, but proximate mechanisms explaining the maintenance and early evolution of kin recognition are still poorly understood. Social spiders provide an intriguing model system to investigate this issue, as some species show kin recognition but a less pronounced complexity of social interactions than that of eusocial insects. Social spiders only hunt and feed communally. Groups of close relatives perform better resulting in a higher individual fitness. Behavioural differences do not explain the better performance. Using proteomic analyses, this project will explore the possibility that a kin-specific investment in the extra-oral digestion and/or a kin-specific compatibility of the digestive enzymes is/are responsible for the better performance of related spiders. Our study object will be the sub-social spider Stegodyphus lineatus (Eresidae) in which kin recognition has been found. This species is an excellent study organism to help resolving one of the long-lasting questions in evolutionary biology, how cooperation can be evolutionarily stable.We will apply different proteomic analyses to identify the enzymatic compounds of the spiders’ digestive fluids and compare their relative composition among related and unrelated individuals. As the genome of our study species has recently been sequenced we will compare the diversity of proteins with the diversity of the according alleles. This will allow conclusions on whether differences are proteomic, genetic or both, and eventually whether this can explain the adaptive advantage of kin recognition.