Snakes and spiders are prototypical threat-stimuli that may trigger automatic avoidance reactions. Using a naturalistic paradigm, we show that humans withdraw their arm from photos of snakes and spiders faster, and with higher acceleration when compared to bird and butterfly stimuli. This was specific to withdrawal: approach, or button-press/release tasks failed to detect a similar difference. Using electroencephalography (EEG), we show that the fast withdrawal was mediated by two attentional processes. First, fast withdrawal responses correlated with early amplification of sensory signals (P1, 70-110 ms after stimulus). Second, a later correlate of feature-based attention (early posterior negativity, EPN, 200-240 ms after stimulus) revealed the opposite pattern: Stronger EPN was associated with slower behavioral responses, suggesting that the deployment of attention towards threatening stimulus features was detrimental for withdrawal speed. The results suggest that fast withdrawal is based on reflex-like attentional processing, and needs to be measured using a naturalistic paradigm.