Williamson County is home to five species that are listed as endangered.

Three of the endangered species are karst invertebrates that live in karst areas.  A karst is the name for the honeycomb type limestone formations (including caves, sinkholes and fissures) that are typical in limestone geology.

• The Bone Cave harvestman (Texella reyesi) is a spider found primarily in Williamson County.
• The Tooth Cave Ground Beetle (Rhadine persephone) is a tiny, reddish-brown beetle that spends its entire life underground.
• The Coffin Cave mold beetle (Batrisodes texanus) is a small, long-legged beetle that lives in total darkness and has no eyes.  This beetle is found only in Williamson County.

Karst Invertebrates Brochure

Two endangered birds also nest in Williamson County.

• The golden-cheeked warbler (Dendroica chrysoparia) is a migratory songbird that builds nests of juniper or cedar bark then binds them with collected spider webs.  They winter in Central America.
• The black-capped vireo (Vireo atricapillus) is another migratory songbird that builds its nests just a few feet from the ground.

The Georgetown Salamander (Eurycea naufragia) is a candidate species in the county that was recently petitioned to be listed as endangered.