Oxidus gracilis
A small flat-bodied millipede of the Lowland Meadow, Oxidus gracilis is recognized by its broad lateral keels and processes decaying plant matter and fungi in moist leaf litter; one of the most widespread introduced millipedes in tropical gardens worldwide, the Lowland Meadow introduction did not establish.
A small flat-bodied millipede of the Lowland Meadow, Oxidus gracilis is recognized by its broad lateral keels and processes decaying plant matter and fungi in moist leaf litter; one of the most widespread introduced millipedes in tropical gardens worldwide, the Lowland Meadow introduction did not establish. Approximately 12 individuals were introduced in July 2024; the population declined steadily and is now Extirpated.
Oxidus gracilis (flat-backed millipede, garden millipede) is a small polydesmid millipede native to East Asia and now widely established in tropical and subtropical regions globally through the horticultural and greenhouse trade. Adults typically reach 18 to 22 mm in length. The body is distinctly flattened dorso-ventrally, with prominent lateral paranota (keels) projecting from each body segment; this flattened profile is the most visible feature separating O. gracilis from the cylindrical spirobolid millipedes (such as the Rusty Millipede). Coloration is typically dark brown to grayish-black, with pale to cream or reddish-orange margins on the paranota. The flattened body shape is characteristic of the order Polydesmida and allows these millipedes to press tightly against substrate surfaces when disturbed.
O. gracilis is a detritivore, feeding on decaying plant matter, fungi, and soft organic debris in the leaf-litter layer and moist soil. It is strongly associated with moist microhabitats and is desiccation-sensitive, retreating under debris, bark, or into soil during dry conditions. In South Florida gardens and disturbed moist habitats, O. gracilis is one of the most commonly encountered millipede species, often found under potted plants, leaf litter, wood debris, and organic mulch.
As a member of the order Polydesmida, O. gracilis possesses ozopores on the paranota connected to defense glands capable of producing hydrogen cyanide (HCN). When disturbed, the millipede may release this chemical defense, which deters many invertebrate predators. The effectiveness of this defense varies with predator size and species.
Unlike Trigoniulus corallinus, which coils into a tight cylinder when threatened, O. gracilis typically flattens against the substrate rather than conglobating. This difference in defensive posture reflects the fundamental body-plan difference between the two orders.
In the Lowland Meadow, Flat-backed Millipede would have functioned as a leaf-litter detritivore, fragmenting decaying plant matter and organic debris in the soil layer and contributing to nutrient cycling at the terrestrial detrital base. The introduced population of approximately 12 individuals declined steadily and did not persist long enough to establish a measurable detrital processing role. Two probable factors in the failure: insufficient accumulation of decaying organic matter and fungi in the relatively young Lowland Meadow substrate to meet the introduced group's dietary requirements, and predation pressure from Wolf Spider and other ground-level predators.
Introduction context: Approximately 12 individuals introduced to the Lowland Meadow in July 2024. Exact date and source not on file.
Approximately 12 individuals introduced to the Lowland Meadow in July 2024; exact date and source not on file. The population declined steadily and did not persist. Two probable contributing factors: insufficient decaying organic matter and fungi in the Lowland Meadow substrate to sustain the introduced group's dietary requirements, and predation pressure from Wolf Spider (Lycosidae sp.) and other ground-level predators present in the Lowland Meadow. No specific decline events or confirmed predation were documented. Extirpated.
Detritivore. Processes leaf litter and decaying organic material in the Lowland Meadow. Millipede detritivory fragments organic matter and increases surface area for microbial decomposition, contributing to nutrient cycling at the terrestrial detrital base. Complements Woodlouse and Earthworm as a detrital processor in the terrestrial realm. No direct feeding observation was recorded before the population was lost.
Oxidus gracilis is adapted to warm tropical and subtropical conditions. As an introduced species now widespread in South Florida gardens and disturbed habitats, it tolerates subtropical heat and humidity. Requires consistently moist soil and leaf-litter microhabitats; sensitive to desiccation. Multiple generations per year possible under Florida subtropical conditions.
Females lay eggs in moist soil or organic debris. Juveniles hatch with fewer leg pairs and body segments and add segments with each successive molt. Multiple generations per year are possible under Florida subtropical conditions. No reproduction was documented in the miniBIOTA Lowland Meadow introduction before the population was lost.
Follow this species across the habitats where it currently appears in the miniBIOTA biosphere.
