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7. Pilosity
Thick, long hair is called seta. In this book, it is sometimes called long hair. The term pilosity usually indicates groups of such hair. Short, fine hair is called pubescence. Pubescence and long hair often coexist. The number of seta (long hair) on particular sites is sometimes important, e.g., when distinguishing different species of the genus Formica. Distinction between different species is sometimes based on whether the hair density is relatively high or low.
Depending on the approximate angle of hair from the skin, hair is roughly divided into standing and lying down hair. Standing hair includes erect hair (almost vertically standing hair), suberect hair (hair standing at an angle of 70-80 degrees from the skin) and subdecumbent hair (45 degrees from the skin). Lying down hair include decumbent hair (10-40 degrees from the skin) and appressed hair (almost parallel to the skin). The number of standing hair on the antennal segments and the tibia is important for distinction between different species of the genus Lasius.
Depending on the shape, hair can be divided into branched hair (with two or more branches), plumose hair (with sawtooth-like side branches) and squamate hair (flat, scale-shaped hair).
(Comments by Kazuo Ogata)