Formicinae is a subfamily of ants. They have a waist with a single segment: the petiole. This is a scale or node like. The gaster has five segments visible from above in females. The sting is absent and the anal aperture is pointed and fringed with hairs: the acidopore. Formic acid is produced and can be emitted from the acidopore. There are two genera common in Britain and Ireland with a third only found in the Channel Isles. They are Formica, Lasius and Plagiolepis.