Benzaldehyde
Guides
Apheloria
cherry millipedes, flat-backed millipedes
Apheloria is a genus of large, chemically defended millipedes in the family Xystodesmidae, distributed across eastern North America. These millipedes are notable for producing hydrogen cyanide and benzaldehyde as defensive secretions, which imparts a characteristic cherry or almond odor. The genus participates in Müllerian mimicry rings in the Appalachian Mountains, with species displaying highly variable aposematic coloration involving black backgrounds with contrasting yellow, orange, red, or white markings. Species-level identification requires examination of male gonopod morphology due to extensive color polymorphism and convergent color patterns among co-occurring species.
Promecognathus
Promecognathus is a genus of ground beetles comprising two described species, P. laevissimus and P. crassus. These beetles are specialist predators of cyanide-producing flat-backed millipedes in the family Xystodesmidae. They possess exceptional physiological tolerance to hydrogen cyanide, surviving doses 7–15 times greater than those lethal to other carabid beetles. This tolerance allows them to attack millipedes directly without behavioral avoidance of chemical defenses, representing the first documented case of cyanide tolerance in predatory insects.