Macrobdella decora

Geographic Range

North American medicinal leeches ( Macrobdella decora ) are native to the Nearctic region. They can be found in the United States of America, Canada, and Mexico. North American medicinal leeches have been reported across multiple regions of the United States, and it is likely they are more widespread than reported. The greatest density of confirmations of these leeches within the United States is in the New England region, which includes Connecticut and Rhode Island. Maine and Massachusetts have also reported a significant number of North American medicinal leeches. The area with the second highest density of confirmations of leeches is in all five Great Lakes of North America. Other confirmed locations include North Carolina, Virginia, Maryland, Delaware, Florida, and Pennsylvania. There are occasional reports of leeches being found from the Midwest, including Illinois, Indiana, Michigan, Wisconsin, and Minnesota. New Mexico has also been reporting high numbers of discoveries of the species. The Rocky Mountains region in Colorado includes several leech reports, as well.

In Canada, these leeches are confirmed to inhabit the eastern areas of the country such as the province of Alberta and the western provinces like Quebec. In Canada there are also numerous findings near the Great Lakes of North America. In Mexico, they are thought to be restricted to Nuevo Leon.

• Biogeographic Regions
• nearctic nearctic
  • native native

Habitat

North American medicinal leeches are found in freshwater and usually live in protected microhabitats like underwater boulders. They inhabit rivers, streams, and lakes. Swamps occasionally host these leeches too. North American medicinal leeches inhabit temperate freshwater, usually in water temperatues between 4 °C and 24 °C. These leeches often inhabit water that is between one and three meters. Leeches often choose murky waters with a thick layer of mud and forest debris in the sediments. This microhabitat provides natural camouflage for leeches. The lakes and streams inhabited by North American medicinal leeches are often surrounded by forests.

• Habitat Regions
• temperate temperate
• freshwater freshwater

• Aquatic Biomes
• lakes and ponds
• rivers and streams

• Wetlands
• swamp swamp

Physical Description

North American medicinal leeches are annelids, possessing a hydrostatic skeleton for support and flexibility. They have around 65 teeth. North American medicinal leeches exhibit orange and green on their ventral side where there are also four and a half circular annuli. These annuli run linear, exact sizes of the annuli are not recorded. The rest of North American medicinal leeches' bodies exhibit a dark green and brown patterned epithelia. This pigmentation is consistent in all life stages of these leeches. The epithelia on these leeches is smooth in appearance with numerous horizontal grooves ranging across the bodies in horizontal stripes. The suckers on the posterior and anterior end of their bodies are darker shades of the main body coloration; and the brown pigments are more prominent than the green pigments. Their bodies exhibit bilateral symmetry, and they are ectotherms. North American medicinal leeches measure between 5 cm to 9 cm in total length and their mass is between 1.5 to 4 g. North American medicinal leeches are hermaphrodites.

North American medicinal leeches hatch after four weeks; these hatchings have pale brown epithelia and lack the coloration of the four annuli on their ventral side. Instead of fully developed coloration of their annuli, the color will be a paler shade. North American medicinal leeches during their juvenile stage are typically 1 cm to 3 cm.

North American medicinal leeches have thinner muscles compared to all other medicinal leeches, like European medicinal leeches ( Hirudo medicinalis ). North American medicinal leeches also have horizontal stripes on their bodies while European medicinal leeches have longitudinal stripes. North American medicinal leeches are ca. 3 cm longer than European medicinal leeches.

• Other Physical Features
• ectothermic ectothermic
• bilateral symmetry bilateral symmetry

• Sexual Dimorphism
• sexes alike

Development

North American medicinal leeches begin their development after fertilization of both the parent leeches. These leeches are hermaphroditic. Both parent leeches exchange sperm and both of their eggs are fertilized. The pregnant leeches will have multiple eggs fertilized within their ovisacs at once. Between one and one hundred eggs will be fertilized and will soon move from the pregnant leeches’ ovisacs to their clitellum. Once the eggs are moved into the clitellum the formation of a cocoon will begin, where all eggs will be packed together. The cocoon is made up of a substance that protects the eggs from exterior harm. After the completed formation of the cocoon, the pregnant leeches will secrete the cocoon out of their body, using their clitellum to push it out. It takes between one month to nine months for the pregnant medicinal leeches to secrete the cocoons. Because North American medicinal leeches live in fresh, shallow, and murky water, the cocoons are often laid in shallow areas where there are protective objects. For instance, fallen trees, rocks, or other vegetation are used to shelter the cocoons.

As the cocoons and eggs take 2 to 4 weeks develop within the sheltered areas, the eggs provide the needed nutrition for the leeches until they are ready to hatch. At hatching, they begin their intermediate life stage before they are adults. Within this intermediate stage the leeches are smaller than the adult leeches, at a length less than 5 cm and a mass less than 1 g. These juvenile leeches will feed on small amphibians like salamanders. While in the juvenile phase, North American medicinal leeches also shed their epithelium until they reach their adult sizes. The juvenile stage of North American medicinal leeches lasts around six months.

The adult stage of North American medicinal leeches is characterized by sexual maturity, the ability for these hermaphroditic leeches to mate and exchange sperm. Adult North American medicinal leeches are also significantly larger than their juvenile stage, the leeches grow to be between one and five centimeters and weigh between 1 and a half grams to five grams. Feeding habits and abilities are also key factors in separating the differences between juvenile and adult leeches. Those with the ability to prey upon and attach to large mammals successfully are adults. For successful attachment to larger prey these leeches must use fully developed anterior and posterior suckers.

As invertebrates, these leeches exhibit indeterminate grwoth.

• Development - Life Cycle
• indeterminate growth indeterminate growth

Reproduction

North American medicinal leeches are hermaphroditic. These leeches search for mates that can provide them with sperm to fertilize eggs in their ovaries, so that they can both become pregnant. They are also polygynandrous, as leeches will mate with multiple partners throughout their lives. No social structures exist within the leeches as they choose multiple mating partners. These leeches will mate with one leech at a time, and year round.

North American medicinal leeches find their mates by using chemical signals. However, limited studies have examined these signals. These pheromones can be detected in the water by sexually-mature leeches. Some studies suggest that physical contact must be made for these pheromones to be detected. No other factors (visual or tactile) come into play regarding mate selection.

Once two North American medicinal leeches have located each other for mating, the two bodies of the leeches will connect vertically in the water. After their bodies have connected using both of their male genitalia, the leeches will spin in the water to mate. The product of mating is a spermatophore that contains the sperm needed for fertilization, transferred between individuals. After mating concludes, each mate will not engage with their partner in any way.

• Mating System
• polygynandrous (promiscuous) polygynandrous (promiscuous)

North American medicinal leeches breed year-round. When fertilized, these leeches will cease breeding for one to nine months, during which eggs within the leeches' bodies are being covered by a cocoon. These leeches typically breed once or twice a year.

North American medicinal leeches are simultaneous hermaphrodites that breed opportunistically year-round. The act of copulation takes minutes, and fertilization can take from one hour to 23 hours. Leeches are oviparous. The 1 to 100 eggs are laid year-round, 1 to 9 months post-mating.

Two to four weeks after the cocoon is released, the eggs will hatch, and the juvenile leeches are fully independent. One to 100 eggs will hatch, with the typical hatching mass unknown. Juvenile leeches are classified as being under 5 cm total length. These leeches reach sexual maturity between one and two years old. North American medicinal leeches are also iteroparous, as they will mate many times and produce many cocoons of eggs throughout their lives.

• Key Reproductive Features
• iteroparous iteroparous
• year-round breeding year-round breeding
• simultaneous hermaphrodite
• sexual sexual
• oviparous oviparous

North American medicinal leeches receive little to no parental care within their life stages. These leeches are hermaphroditic. The pregnant leech will act only as a vessel of development for cocoon formation to the offspring. This protective cocoon will form within the leeches’ body and then be laid in fresh water. After the cocoon is laid by the parental leech, the offspring are left, and the parental leech will not continue any involvement with the offspring.

• Parental Investment
• no parental involvement
• pre-hatching/birth
  • provisioning
    • male
    • female

Lifespan/Longevity

Lifespan and maximum longevity are not reported for North American medicinal leeches. Others in the genus, such as European medicinal leeches ( Hirudo medicinalis ), have an average lifespan of 1 to 3 years. These leeches are kept in captivity, specifically in clinical settings like hospitals and research settings like universities. However, captive lifespans have not been reported.

Pollution within North American medicinal leeches’ environment can severely impact their lifespans. Trash within the lakes, ponds, and rivers have made attaching to prey more difficult because hosts are dying at higher rates. Extreme changes in the usual temperatures of these leeches' environments are also making it more difficult for these leeches to reach adulthood. Colder and warmer water temperature trends in the Great Lakes of the United States are causing these leeches hatch at abnormal rates.

Behavior

North American medicinal leeches are solitary animals, only interacting with other leeches to mate. After mating, partners will not have any contact with the other or the offspring. These leeches do not have social orders or hierarchies. There has not been recorded evidence of intraspecific aggression.

North American medicinal leeches live in murky, freshwater like rivers, ponds, and lakes. They live in shallow sections of these bodies of water sheltered by fallen trees, boulders, plants, or trash to hide from predators and to have ample opportunity to attach to their prey. There have been accounts of these leeches living close to one another in these areas if the environment is favorable.

These leeches are parasitic, as they attach to their prey to consume the blood of the host. Often, they will stay in a small area until they find their prey. If attached to prey these leeches can travel large distances in the air, water, or land. When consuming the blood of their prey they will grow as they fill up with blood. These leeches will detach from their prey when they are full of blood and become too heavy to stay attached. After becoming engorged with blood from their prey they can withstand long periods without food and will often seek prey less. These leeches can also withstand long periods without food, up to 1 year.

These leeches have unique ways of moving within the water. Their bodies are very flexible for efficient water travel. When moving they bend their bodies in an up and down motion to move forward. They can spin and exert small bursts of motion when in danger from predators to swim away quickly. Despite being more active during the night than the day, they are not exclusively nocturnal. These leeches do not sleep but remain inactive for rest periods.

• Key Behaviors
• natatorial natatorial
• diurnal diurnal
• parasite parasite
• motile motile
• sedentary sedentary
• solitary solitary

Home Range

The home range of North American medicinal leeches is very small, between one and fifteen square meters within a freshwater environment including ponds, rivers, and lakes.They do not defend a territory.

As parasites, hosts may move these leeches large distances in air, water, or on land.

Communication and Perception

North American medicinal leeches have little research done on their communication. However leeches do communicate chemically utilizing their anterior sucker to release pheromones from their saliva. Their saliva will then travel within the body of water they inhabit and reach other leeches. Utilizing these pheromones aids in communication for reproduction. Leeches will not seek out conspecifics for reproduction unless their bodies are full of blood. North American medicinal leeches sense vibrations in the water that alerts them about possible incoming hosts. North American medicinal leeches are also able to feel when other organisms brush against their epithelium which enables them to attach to their prey. These leeches also have 5 pairs of eyespots to sense the differences in light and dark in their environment.

• Communication Channels
• visual visual
• tactile tactile
• chemical chemical

• Other Communication Modes
• pheromones pheromones
• vibrations vibrations

• Perception Channels
• visual visual
• tactile tactile
• vibrations vibrations
• chemical chemical

Food Habits

North American medicinal leeches are classified as sanguivorous, feeding on blood. Blood is consumed from their prey by their anterior sucker while the posterior sucker holds onto prey. Blood consumed by these leeches provide a variety of nutrition including proteins, carbohydrates, and irons. Their primary food sources include amphibians such as frogs and salamanders. Leeches opportunistically consume eggs and tadpoles of green frogs ( Lithobates clamitans ). These leeches consume fish eggs from smallmouth bass ( Micropterus dolomieu ) and brook trout ( Salvelinus fontinalis ). North American medicinal leeches will often attach to the body of the fish host’s gills or pharynx. These leeches will opportunistically feed upon birds in rare cases. Often when these leeches attach to birds they attach when the birds walk, fly, or are wading into the water and brush upon the leeches’ bodies. Their flexible epithelia and invertebrate bodies aid them with wind resistance and the rapid movements when feeding on these birds. There have been reports of North American medicinal leeches attaching to ducks such as the American black duck ( Anas rubripes ). They also attach to mammalian hosts, including humans ( Homo sapiens ) and other large mammals when opportunity arises. North American medicinal leeches also successfully attach to prey more during the night compared to morning or afternoon hours. The activity of these leeches decreases during daytime, thus affecting successful attachment and feeding.

• Primary Diet
• carnivore carnivore
  • sanguivore sanguivore

• Animal Foods
• birds
• mammals
• amphibians
• fish
• eggs
• blood

Predation

North American medicinal leeches have three main predator types: birds, reptiles, and fish. All the leeches’ predators hunt for them in freshwater habitats such as rivers, streams, and lakes. Most predators feed opportunistically on these leeches. The only recorded bird species that consume North American medicinal leeches are northern shovelers ( Spatula clypeata ).

Among the fish that eat the leeches are smallmouth bass ( Micropterus dolomieu ). These fish inhabit the freshwater rivers and also serve as leech hosts. Bluegill ( Lepomis macrochirus ) and redear sunfish ( Lepomis microlophus ) consume leeches, the latter eat large quantities of these leeches.

Common snapping turtles ( Chelydra serpentina ) and eastern painted turtles ( Chrysemys picta ) consume North American medicinal leeches, as do eastern garter snakes ( Thamnophis sirtalis ).

Leeches avoid predators by successful escape in water and camouflage – they are a mix of dark green and dark brown with colorful orange spots. The areas in which these leeches inhabit are often under or around rocks, fallen trees, and mud which the leeches will dig into to camouflage against their predators.

• Anti-predator Adaptations
• cryptic cryptic

Ecosystem Roles

North American medicinal leeches are opportunistically preyed upon by birds, reptiles, and fish. These leeches are parasites that attach to fish, frogs, large mammals, birds, salamanders, and fish eggs. There is no report of North American medicinal leeches having parasites.

North American medicinal leeches act as parasites that attach externally to hosts. The main fish these leeches attach to are smallmouth bass ( Micropterus dolomieu ) and brook trout ( Salvelinus fontinalis ). These leeches will also eat the eggs of these fish when they encounter them in the water. Occasionally, these leeches will attach to birds such as American black ducks ( Anas rubripes ) when physical contact occurs. These leeches also attach to large mammals if encountered. North American medicinal leeches are used in medical practice by humans ( Homo sapiens ) which is a role that these leeches have acquired more commonly recently.

Primarily these leeches act as predatory parasites within rivers, ponds, lakes, and steams. In most cases these leeches will remove toxins from their hosts as they feed on them.

• Ecosystem Impact
• parasite parasite

Economic Importance for Humans: Positive

North American medicinal leeches have a variety of economic importances for humans. These leeches are mainly used in medicine for blood treatments and post-surgical treatment. European medicinal leeches ( Hirudo medicinalis ) have been used for centuries, North American medicinal leeches have only been used within the past 200 years. The usage of these leeches in modern medicine is performed with well-researched procedures in hospitals and clinics, where physicians use lab-grown North American medicinal leeches. Lab-grown leeches provide patients with sterile and safe leeches for their treatments. These leeches provide profits to many hospitals and clinics worldwide. The United States of America is the country that records the greatest use of these leeches and these leeches are considered a medical device therein medicine. In many other countries, North American medicinal leeches are also commonly used with European medicinal leeches. European countries' use of medicinal leeches is on the rise.

These leeches are used to treat blood ailments because North American medicinal leeches contain an enzyme called thrombin that prevents the coagulation of blood. It should be noted that North American medicinal leeches are better at feeding on blood than European medicinal leeches because North American medicinal leeches contain more thrombin than European medicinal leeches. Historically, North American medicinal leeches were used in a medical practice called blood letting, where they would be attached to a patient to drain their blood to get rid of toxins in the body and to balance what physicians believed to be the four humors of the body.

North American medicinal leeches are profitable and important in scientific research, mainly in universities, hospitals, and private companies. The research efforts to find more effective leeches for medical use is ongoing and some researchers aim to breed leeches to find variants with larger amounts of the two histamines: hyaluronidase and bdellin within the leech’s bodies. Other researchers are focused on cultivating larger sized North American medicinal leeches. The current price of a singular North American medicinal leech is twelve dollars; however these leeches are often used in bulk to treat humans in the medical setting which increases the price for consumers, thus making them more expensive. The price for bulk use in the medical setting usually starts at one thousand dollars if patients do not have insurance.

• Positive Impacts
• source of medicine or drug source of medicine or drug
• research and education

Economic Importance for Humans: Negative

North American medicinal leeches have not been recorded to cause any adverse effects to humans. However, when they are used in the medical setting they do attach to the skin of the patient through piercing through the skin, leaving an incision millimeters in length. The attachment of these leeches is not painful to humans.

Verriere et al. (2016) found that some leeches used in European medicinal therapy were infected with a harmful bacterium in the genus Aeromonas . Post-treatment infections are rare, but should be monitored to reduce negative human interactions. McClure et al. (2021) confirmed that this bacterium is present in North American medicinal leeches, and therefore poses the same threat.

• Negative Impacts
• injures humans
  • bites or stings
  • carries human disease

Conservation Status

North American medicinal leeches are not evaluated by the IUCN red list, and have no special status on the US federal list, CITES appendices, or the state of Michigan list.

Threats to these leeches include overharvesting from the wild to meet a rising demand for their use in medicinal treatments. Once removed from the wild, these leeches are grown in sterile lab conditions. Threats in the wild also include predators and droughts, which reduce suitable aquatic habitats.

Currently, North American medicinal leeches are lab grown for medicinal use in hospital and clinical settings. The captive breeding, raising, and distribution of these leeches is one of the only conservation efforts today. North America BioPharma is a large private company that sells medicinal leeches to the public. This company currently sells European medicinal leeches ( Hirudo medicinalis ) but is expanding to include North American medicinal leeches.

Additional Links

Encyclopedia of Life

Contributors

Fiona Steinour (author), Radford University, Natalie May (editor), Radford University, Alexander McVicker (editor), Radford University, Karen Powers (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.

References

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