Leeches are invertebrates belonging to the phylum Annelida, making them segmented worms closely related to earthworms. Found across nearly all continents, leeches inhabit various aquatic and moist terrestrial environments. They are a natural component of many ecosystems, including those found throughout California.
Preferred Aquatic Environments
In California, leeches primarily inhabit freshwater environments such as lakes, ponds, slow-moving streams, and marshes. They are most commonly found in shallow, protected areas where water currents are minimal. These preferred habitats often provide abundant shelter, including aquatic plants, submerged stones, logs, and other debris.
Water quality and the presence of vegetation are important for suitable leech habitats. Leeches are moderately tolerant of pollution and low oxygen conditions, and their presence can sometimes indicate poor water quality if found in unusually high densities. They often cling to solid substrates like rocks and plants, or hide within detritus, as they require a hard surface for movement using their suckers. Areas with soft, silty substrates are generally less favorable for leeches due to their inability to attach effectively. The availability of host animals, such as fish, amphibians, and other invertebrates, also influences where leeches can thrive, as many species are parasitic or predatory.
Common California Leech Species
California is home to several common leech species, exhibiting varied feeding habits and distributions. One species is Haemopis marmorata, often referred to as the American medicinal leech or horse leech. This species is primarily an opportunistic predator and scavenger, known to feed on small invertebrates and sometimes amphibian eggs and tadpoles. It is widely distributed across North America and found in various freshwater bodies. These leeches are typically robust, reaching several inches in length, and can be dark brown or mottled in appearance.
Another species found in California is Erpobdella punctata, also known as the tiger leech. Unlike some blood-feeding leeches, Erpobdella punctata is a predator and scavenger, consuming copepods, midges, earthworms, and amphipods. This species is widespread across North America, inhabiting both ponds and streams. They are smaller than Haemopis marmorata, ranging from 20-50 millimeters (0.8-2.0 inches) in length, and lack true jaws.
Placobdella parasitica, a blood-feeding leech, has also been reported in California. This species is an opportunistic feeder on turtles, and its presence in California is linked to the introduction of exotic turtles from the eastern and central United States. Placobdella parasitica is differentiated by its smooth dorsal surface and often has 8 to 12 stripes on its abdomen. Additionally, Helobdella californica, known as the “Golden Gate leech,” is a smaller leech primarily found in the freshwater ecosystems of Golden Gate Park in San Francisco. These leeches are small, less than 2 centimeters, and feed on insect larvae and other small aquatic invertebrates.
Encountering Leeches in California
Encounters with leeches in California’s natural waters are common, especially during warmer months. Most leeches found in California are not harmful to humans and do not transmit diseases. If a leech attaches, it will feed for a period and then detach on its own. The main concern after a leech attachment is minor irritation or a localized infection if the bite area is not properly cleaned.
To remove an attached leech, use a fingernail to gently dislodge it, rather than pulling forcefully. After removal, the bite should be thoroughly cleaned, disinfected, and bandaged, similar to any other minor cut. Leeches release anticoagulants, so the bite site may ooze for several hours. While the experience can be unsettling, California’s leeches are a natural part of the ecosystem and pose minimal health risks. Swimming in deeper waters and areas free of dense aquatic vegetation or debris can reduce the likelihood of an encounter.