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Description: Across animal taxa, many species show repeatable among-individual differences in behaviour. Such behavioural individuality can affect ecological and evolutionary processes, including invasion success, population dynamics, and speciation, with social spiders rapidly becoming showcase model systems. The validity of conclusions derived from these studies hinges critically on the untested assumption that behavioural individuality persists over ecologically relevant timeframes. Here we show this assumption to be false for an emerging model, the social spider Stegodyphus dumicola. We assayed individuals repeatedly over a major part of their lifetime. Repeatable behavioural differences were initially present but faded within weeks and failed to predict behaviour later in life. This implies that downstream links with ecological or evolutionary processes cannot result from genuine behavioural individuality. Rather, individual differences must stem from environmental variance simultaneously inducing pseudo-repeatability: the appearance of behavioural individuality where none exists. Research paradigms commonly used in animal behaviour and human psychology, where individuals are “typed”, shown to be “repeatable”, and then used to predict evolutionary outcomes, should thus be considered with extreme caution. Progress requires firmly quantifying animal behaviour over an entire lifetime to unequivocally link individuality to ecology and evolution.