Xystocheir dissecta

As a flat-backed millipede (order Polydesmida), X. dissecta has a dorsoventrally flattened body form with lateral extensions (paranota) on each segment. The species can be distinguished from other xystodesmid millipedes in its range by its specific coastal Northern California distribution and, when threatened, its production of hydrogen cyanide gas with benzaldehyde as a detectable byproduct. The three subspecies differ in subtle morphological features: X. d. dissecta (the nominate subspecies), X. d. microrama (described 1996), and X. d. taibona (described 1912).

Coastal and near-coastal environments in Northern California. Found in oak woodlands, which cover extensive areas of its range. Activity is moisture-driven, with millipedes becoming active during periods of adequate soil moisture.

Restricted range in North America, primarily in and around the San Francisco Bay Area along the coast of Northern California. The range is smaller than that of its specialist predator, Promecognathus beetles.

Activity correlates with seasonal moisture patterns, peaking during periods of winter and spring rains. At higher elevations and northern parts of the range, colder winters push activity to later spring and early summer. During dry conditions, individuals become inactive and difficult to locate.

When threatened, individuals release hydrogen cyanide gas from paired glands along the sides of each body segment. This chemical defense is effective against most beetle predators. The millipede responds to attack by twisting, thrashing, and curling into a tight ball to shield its underside. Defensive secretions are released through microscopic openings in each gland, sometimes at mere touch.

Prey for specialist predators, particularly beetles in the genus Promecognathus (Carabidae). The species' chemical defense system and the unique cyanide tolerance of Promecognathus represent a documented predator-prey evolutionary arms race. The almond-smelling benzaldehyde byproduct of cyanide production may serve as an olfactory warning signal to potential predators.

The hydrogen cyanide defense can cause eye irritation and headaches in humans when millipedes are observed in poorly ventilated enclosed spaces. The species has been featured in scientific media including PBS Digital Studios' Deep Look series, highlighting its toxic relationship with cyanide-tolerant beetles. Research on this species and its predators has potential medical applications for understanding cyanide tolerance mechanisms.

• Other Xystocheir speciesCongeneric millipedes in the genus Xystocheir share the flat-backed body form and cyanide defense; identification to species level requires examination of gonopod morphology and geographic distribution.
• Other PolydesmidaMany flat-backed millipedes in the order Polydesmida possess similar cyanide-producing glands; species identification relies on detailed morphological examination and geographic range.

• millipede
• cyanide defense
• chemical defense
• California endemic
• flat-backed millipede
• Xystodesmidae
• Promecognathus prey

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• These Beetles Withstand Cyanide Blasts to Eat Millipedes
• Halictidae | Beetles In The Bush