Dark Banquet - Bill Schutt [52]
Many other leeches are quite adept at swimming, but unlike fish, which move by undulating from side to side, leech bodies bend with an up-and-down motion that is reminiscent of dolphins and whales. Leonardo Da Vinci (1452–1519) may have been the first to study leech locomotion and he actually spent quite a bit of time getting the intricacies of their dorsoventral undulations just right.
Unlike the parasitic torpedo attack launched against Bogart’s character in the 1951 classic The African Queen (those “leeches” were actually made out of rubber), there are aquatic leeches that gain access to their hosts via different routes. Some hop aboard as their victims dip their heads for a drink. Entering through the nostrils, the leeches attach themselves to the mucous membranes that line their host’s nasal cavity. There, in the warm, humid chamber, they feed and mature, safe from detection—at least for a while.
One famous story recounts how this type of leech attack afflicted a group of Napoleonic soldiers, crossing from Egypt to Syria in 1799. As with any army in a foreign land, obtaining water was always a major concern and things were even dicier in the days before purification techniques (like boiling or adding iodine or chlorine) could make most water at least semisafe to drink. Apparently, some of these men drank water from a lake infested with tiny larval leeches. Unbeknownst to their hosts, the creatures quickly attached themselves and began to feed. Days later the men began to take ill and medical personnel were horrified to find their patients’ noses, mouths, and throats carpeted by blood-engorged leeches. The doctors tore frantically at the vampires and it’s not hard to envision a gory scene made all the more horrible by the cries of fearful, frantic men.
As in other similarly large groups of animals, there is a wide degree of variation in leech diets. About three-fourths of all known species are bloodsucking parasites, feeding primarily on the blood of vertebrates (including sharks, bony fishes, frogs, turtles, snakes, crocodiles, birds, and mammals). Parasitic leeches do not generally specialize on any one particular prey. For example, the medicinal leech Hirudo medicinalis usually feeds on frogs, but it will readily take human blood. And while we’re on the topic, it should also be noted that dietary relationships between leeches and other organisms aren’t all stacked in the leech’s favor. Leeches are commonly fed upon by fish, birds, salamanders, snakes, and even other leeches.
According to Dr. Mark Siddall, a leech expert and curator at the American Museum of Natural History, the first leeches were freshwater blood feeders, but alternative feeding modes have evolved at least six times in various leech groups. Several of these lineages have become predators, feeding solely on invertebrates (like their earthworm cousins, snails, or even other leeches). Unlike parasitic leeches, which can survive for extended periods of time without feeding, predaceous leeches feed frequently (generally, every one to