Some venomous cone snails feed on small fishes using an immobilizing combination of synergistic venom peptides that target K _v and Na _v channels. As part of this envenomation strategy, δ-conotoxins are potent ichtyotoxins that enhance Na _v channel function. δ-Conotoxins belong to an ancient and widely distributed gene superfamily, but any evolutionary link from ancestral worm-eating cone snails to modern piscivorous species has not been elucidated. Here, we report the discovery of SuVIA, a potent vertebrate-active δ-conotoxin characterized from a vermivorous cone snail ( Conus suturatus ). SuVIA is equipotent at hNa _V 1.3, hNa _V 1.4 and hNa _V 1.6 with EC ₅₀ s in the low nanomolar range. SuVIA also increased peak hNa _V 1.7 current by approximately 75% and shifted the voltage-dependence of activation to more hyperpolarized potentials from –15 mV to –25 mV, with little effect on the voltage-dependence of inactivation. Interestingly, the proximal venom gland expression and pain-inducing effect of SuVIA in mammals suggest that δ-conotoxins in vermivorous cone snails play a defensive role against higher order vertebrates. We propose that δ-conotoxins originally evolved in ancestral vermivorous cones to defend against larger predators including fishes have been repurposed to facilitate a shift to piscivorous behaviour, suggesting an unexpected underlying mechanism for this remarkable evolutionary transition.