Ectoparasites that feed on blood must possess some structure that allows them to penetrate the epidermis and reach blood vessels.
Fleas have mouthparts adapted for peircing and sucking.
Ticks insert their chelicerae and hypostome through the host's skin.
The sucking lice have a haustellum (H) adapted for sucking. Note the absence of mandibles around the mouth.
Even the so-called chewing lice can feed on blood. Their mandibles (M) can chew a hole in the epidermis and draw blood.
