Harpalinae is the largest subfamily of ground beetles, containing more than 19,000 species worldwide.
thumb|293x293px|Chlaenius purpuricollis, a member of Harpalinae in the tribe Chlaeniini.
thumb|207x207px|Panagaeus fasciatus, a Harpalinae species within the tribe Pangaeini.
thumb|315x315px|Pterostichus pedemontanus, another member within Harpalinae, in the tribe Pterostichini.
Biology
This subfamily contains the most apomorphic ground beetles, displaying a wide range of forms and behaviors. The morphology of species within Harpalinae range from ant-mimics to charismatic members within the genus Pterostichus. Some exhibit rare feeding habits among ground beetles, including both omnivorous and even herbivorous species. Some members of Harpalinae, especially those restricted to the tropics, are considered to be arboreal. This variety of habitats has been considered to lead to the wide diversification of morphological traits.
Systematics
Recent phylogenetic analysis of Harpalinae has placed approximately 19,000 species within around 40 tribes in this subfamily Few subfamilies within Carabidae have been recovered as supported. As mentioned above, members in Harpalinae evolved to be arboreal. The evolution of these members involved multiple gains and losses of characters, with the evolution of arboreality originating and reversing several times.
Ecology
Members of Harpalinae fulfill a variety of ecological niches. These include various symbioses with other insects, ovoviviparity, and even ectoparasitism. Members of Harpalinae are even considered agents of biological pest control, especially in agricultural settings. While likely not having co-evolved with the angiosperms, angiosperm radiation likely lead to the diversification of ecological niches in Harpalinae.