Xystocheir

Flat-backed millipedes in this genus can be distinguished from other polydesmidan millipedes by their California endemic distribution and membership in the tribe Xystocheirini. Species-level identification requires examination of gonopod morphology and other subtle anatomical features. The genus is characterized by the presence of cyanide-producing glands along the sides of each body segment, a trait shared with many Polydesmida but particularly well-developed in Xystodesmidae.

Found in oak woodlands and associated habitats in the Coast Ranges and Sierra Nevada of California. Activity is moisture-driven, with populations becoming difficult to locate during dry periods.

Endemic to California, United States. Distributed in the Coast Ranges and Sierra Nevada. Xystocheir dissecta has a particularly restricted range centered on the San Francisco Bay Area.

Activity peaks in late winter to early spring in most of the range, correlating with winter rains. At higher elevations and northern portions of the range, activity shifts to later spring and early summer due to colder winters. During dry conditions, individuals become inactive and difficult to find.

When attacked, individuals twist violently and curl into a tight ball to shield the vulnerable underside while simultaneously releasing cyanide gas from lateral glands. The defensive secretion contains hydrogen cyanide and benzaldehyde, which produces an almond-like odor. Xystocheir dissecta has been observed to fluoresce under ultraviolet light.

Serves as a specialized prey item for the beetle genus Promecognathus, which has evolved exceptional tolerance to cyanide specifically to exploit this food source. The millipedes' chemical defense excludes most other potential predators, creating a niche with limited competition.

Xystocheir dissecta has been used in research on predator-prey chemical ecology, specifically studies of how Promecognathus beetles withstand cyanide. The species' fluorescence under black light has been noted in forensic entomology contexts. The cyanide defense can cause eye irritation and headaches in humans exposed to concentrated emissions in enclosed spaces.

• Other PolydesmidaDistinguished by California endemic distribution and tribe-level classification; many other flat-backed millipedes lack the specific combination of geographic restriction and gonopod morphology found in Xystocheir.
• Other XystodesmidaeRequires detailed examination of male gonopods and other subtle morphological characters for definitive identification; the tribe Xystocheirini is endemic to western North America.

• cyanide defense
• fluorescence
• California endemic
• chemical ecology
• oak woodland

• BugGuide
• Wikipedia
• GBIF taxonomy match
• NCBI Taxonomy
• Catalogue of Life
• They'll Light Up Your Life | Bug Squad
• These Beetles Withstand Cyanide Blasts to Eat Millipedes