Microcina homi

Hom's Micro-blind Harvestman

Family: Phalangodidae · Class: Arachnida · Order: Opiliones

Conservation status: G1 S2

Horn's microblind harvestman is a small arachnid endemic to serpentine soils in the San Francisco Bay Area. This species belongs to the order Opiliones, commonly known as harvestmen or daddy longlegs, but differs from typical harvestmen by its extremely reduced or absent eyes and small body size. Like other members of the genus Microcina, this species has adapted to life in the soil and leaf litter of serpentine habitats, where light penetration is minimal. The species occurs exclusively within the serpentine soil ecosystems of the San Francisco Bay region. According to the Recovery Plan for Serpentine Soil Species, Horn's microblind harvestman is found in association with other rare serpentine-adapted invertebrates including related species such as Jung's microblind harvestman (Microcina jungi) and Tiburon microblind harvestman (Microcina tiburona) (USFWS 1998, p. 108). The precise distribution appears to be highly restricted to specific serpentine outcrops within this region. This species inhabits serpentine soils, which are derived from ultramafic rocks and characterized by high concentrations of magnesium and heavy metals such as chromium and nickel (USFWS 1998, pp. 6-8). These soils support unique plant communities and create harsh growing conditions that exclude most plant species. The serpentine soil environment provides the specialized microhabitat requirements for Horn's microblind harvestman, likely within soil crevices, under rocks, or in the root zone of serpentine-adapted vegetation. These soils typically have poor water retention and extreme pH levels. As a soil-dwelling harvestman, this species likely feeds on small invertebrates, detritus, and organic matter found within the serpentine soil matrix. The reduced eyes suggest adaptation to a subterranean lifestyle where visual cues are less important than chemical and tactile senses for locating prey and mates. Like other harvestmen, reproduction likely involves direct transfer of sperm, with females depositing eggs in protected soil crevices. Seasonal activity patterns and specific prey preferences have not been well documented for this species. Horn's microblind harvestman has a global rank of G1, indicating it is critically imperiled globally, and a state rank of S2, meaning it is imperiled in California (USFWS ECOS 2025). The species is listed as a Species of Concern in the Recovery Plan for Serpentine Soil Species of the San Francisco Bay Area (USFWS 1998, p. 108). Primary threats include habitat destruction from urban development, recreational activities, and invasive plant species that alter serpentine grassland communities (USFWS 1998, pp. 110-112). The naturally fragmented distribution of serpentine soils makes populations vulnerable to local extinctions. Climate change may pose additional threats through altered precipitation patterns affecting soil moisture regimes. Conservation efforts focus on protecting remaining serpentine grassland habitats and managing invasive species that threaten these unique ecosystems.

Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, and more.