Stylostome
The stylostome is a funnel or channel-like structure formed in response to trombiculid mites. The formation is not caused by the mouthparts of the mites, because these mites do not have needle-like mouthparts as other hematophagous animals have been known to have, but have chelicerae, which only pierce the skin. The tube is formed by the digestive enzymes in the saliva, which is the same salivary secretions that break down cells that is causing the surrounding tissue to harden. As the mite feeds longer, the saliva seeps farther down, and digesting more tissue, therefore causes the stylosome to penetrate to lower layers of skin.
Transmission of disease
Normally, the bite mark causes local swelling or welts, but in more serious cases it causes dermatitis. The mite can be infected with a disease called scrub typhus in Asia and the Pacific by carrying saliva directly to the blood stream, but mites in North America have not been known to transmit Lyme disease, Rocky Mountain spotted fever, tularemia or any other disease. See Mites of livestock for a photograph of a trombiculid with its stlyostome.