Though they are known best for their famous and at times infamous use in the practice of medical bloodletting, particularly during the Middle Ages, not all leeches are bloodsucking creatures – and despite common misconceptions, the vast majority of leeches are harmless to humans. Though the sight of a leech can make some people queasy, a surprising number of people celebrate the odd creatures: Particularly in fishing communities and in areas near ponds and lakes, leeches are kept as pets or farmed at home, either for medical purposes or as a treasured source of fishing bait. If you're curious and patient, raising leeches in an aquarium yourself is a relatively easy task.
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Leeches are a type of annelid, a segmented worm in the same family as earthworms. Leech breeding is easily accomplished in an aquarium, where leeches can live for anywhere from a few months to a few years in dechlorinated tap water, depending on the specific leech species. So long as their water is changed regularly and the leeches are kept fed, the worm relatives will breed on their own.
There are over 600 different species of leech known today, found all across the planet: leeches, whether they live on land or are completely aquatic, are one of the few types of animals that can be found on or around every single continent, including Antarctica, where leeches can be found in the coastal waters. They are a type of annelid – segmented worms, related to the more common earthworm – and do not all drink blood, despite the popular portrayal of the creatures. Some leech species are predators that eat other animals, some are parasitic and others eat organic debris. Part of what makes leech breeding so easy is the fact that leeches are hermaphroditic animals, meaning that every leech possesses both male and female sex organs; in other words, any two adult leeches of the same species can mate with each other.
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To start raising leeches in an aquarium at home, first acquire a few leeches – either from a local pond or lake (where you'll need to identify the species) or by purchasing them online. Aquatic leech species should be kept in an aquarium filled with fresh, dechlorinated (but not distilled) water, while amphibious or land-based leech species should have an environment tailored to them, with rocks and plants and some dechlorinated water nearby. The aquarium should be kept at a stable temperature range, and there should be a lid or tightly secured fabric over the aquarium, allowing air to pass through but preventing the leeches from escaping. Depending on the species of leech, the annelids can live for a few months to a few years – and depending on the species and their preferred food, they may only need to be fed once every few months. Water should be changed weekly in portions, to keep the environment stable without shocking the leeches.
The process of breeding leeches and establishing a leech farm is a simple process. So long as two adult leeches are in the same habitat, and both have been fed recently, it is possible for the leeches to mate. Mating leeches will coil around each other in a mesmerizing, dance-like motion, after which one of the leeches will produce a cocoon containing its eggs. Depending on the species, the leech will either carry the cocoon on itself or attach the cocoon to a feature of the habitat – at which point snails, frogs or small fish (depending on species) may need to be introduced to the habitat to act as a food source for the young leeches. While the exact hatching time will depend on the leech species and the temperature, once hatched the newborn leeches will take somewhere between two weeks and four months to mature – at which point they may participate in the breeding process. To expand your leech farm, simply move a few leeches to a new habitat and maintain it as you did the first.
Because a small number of leeches in a comfortable environment can reproduce in large numbers, many leech owners sell off their extra leeches for some profit. Most farmed leeches today are sold as live bait for use in fishing, where they are treasured for their effectiveness in luring bass, catfish, pike and other prized fish – but a resurgence in the medical use of leeches has led to a growing market of medical-grade leech farms. While the process of raising and selling medical-grade leeches can be difficult – involving FDA certification in the United States; the use of a single, specific species of leech; and a series of complex and expensive care methods – selling farmed leeches as bait requires only a commercial bait or fish dealer's license, acquired through your state's department of wildlife conservation (or similar office). Though it will depend on your state's requirements, which will vary depending on the local fishing industry, these licenses are often fairly inexpensive to apply for and obtain, and will generally last for a year before needing to be renewed.