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Why are lice flattened from top to bottom?

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human head louse — louse Human head louse (*Pediculus humanus*).

Lice have bodies that are flattened dorsoventrally (from top to bottom) to allow them to lie closely against the feathers or hairs of their host. This physical adaptation enables them to remain securely attached while feeding or moving within the ecological niches provided by the host's body.1