Field Guide to Venomous and Medically Important Invertebrates ...

and continues until the leech is engorged. During engorgement a leech may take up several
times its own weight in blood. The speed of engorgement varies, although leeches can ingest a
surprising amount of blood in only a few minutes. Because blood-feeding leeches often ingest
several times their body weight in blood at a single feeding and they digest their food slowly,
they may go months between blood meals.
Blood ingested by leeches is mixed with salivary fluid containing an anticoagulant known as
hirudin or hemetin depending on the group of leeches involved. These compounds prevent blood
from clotting thus allowing the leech to freely feed. When the leech either drops from the host or
is pulled loose, blood continues to flow from the attachment site for up to an hour and the wound
may ooze for up to 5 hours. Also, there may be delayed irritation and itching associated with the
wound. Secondary infections associated with the bite site can occur and such areas should be
washed and treated with an alcohol or similar disinfectant solution after a leech is removed or
falls off following feeding. However, the most significant threat posed by leeches arguably is
one of a psychological disturbance.
Land leeches are quickly aroused when vegetation is moved or when a person walks through an
area. Body odor of the host, movement, respiratory carbon dioxide, and perhaps other factors
attract leeches to their hosts. Aroused land leeches "stand up" in a characteristic reaching
attitude and sway in different directions when a host animal is close by. Upon the slightest
contact with a host, they will attach the anterior sucker, and then commence exploring for a
suitable attachment point. In doing this they may enter any opening in clothing and have been
known to go through eyelets of boots or through the fabric in loosely woven cloth. They may