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Page 281 Allomones are defensive chemicals used by many small and slow moving animals for protection against predators. These irritant chemical mixtures are widespread in arthropods and often contain aldehydes as constituents such as (E)-2-alkenals which contain a double bond between the alpha and beta carbon atoms. The chain lengths of these repellents can vary in chain length which is in the range of 6–12 carbons in many species. (E)-2-alkenals effectively deter numerous predators including ants, mantids, lizards, birds, and mice. However, it remained unknown how these chemicals are sensed and elicit their repulsive action. Blair et al. tested the hypothesis that (E)-2-alkenals’ repulsive actions involve the activation of chemesthetic pathways through transient receptor potential (TRP) channels. Heterologous expression studies revealed that low concentrations of (E)-2-alkenals activate TRP ankyrin subtype 1 (TRPA1) channels, whereas other TRP channel types were only weakly or not activated. TRPA1 was also sensitive to related compounds such as hexanal, decanal, and (E)-2-hexen-1-ol, yet with weaker potency. Thus, the data suggest that TRPA1 is a likely target for (E)-2-alkenal-type deterrents.