{{Short description|Species of leech}} {{Featured article}} {{Speciesbox | image = Macrobdella decora white background.png | image_alt=A large, unflattened leech on a white background. The back is olive-brown with a series of orange points; the belly is dull orange. | taxon = Macrobdella decora | authority = (Say, 1824) | range_map = M. decora range.png | range_map_caption = {{legend|#f56969|Observed}} | range_map_alt = Map showing distribution of Macrobdella decora in eastern North America, centred around the Great Lakes and the eastern coastline. | synonyms = {{Species list | Hirudo decora | Say, 1824}} | synonyms_ref = <ref>{{cite WoRMS |title=''Macrobdella decora'' |id=160023 |access-date=5 January 2025}}</ref> | name = North American medicinal leech }}
'''''Macrobdella decora''''', also known as the '''North American medicinal leech''', is a species of leech found in much of eastern North America in freshwater habitats. ''M. decora'' is a parasite of vertebrates, including humans, and an aquatic predator of eggs, larvae, and other invertebrates. It is a medium-sized leech with a spotted greenish-brown back and a reddish or orange underbelly with black spots. It has ten ocelli, or simple eyes, arranged in a horseshoe shape, as well as three long jaws. Internally, a pharynx takes up a tenth of its digestive tract; a stomach, the majority of its body length. The stomach connects to an intestine, followed by a colon, a rectum, and finally an anus located on the leech's back. ''M. decora'', like all leeches, is hermaphroditic, and has twenty testisacs and two ovisacs, in addition to male and female genital pores. First described by Thomas Say in 1824, the species is now placed in the genus ''Macrobdella.'' Its closest relative is believed to be the species ''Macrobdella diplotertia''. It is not considered to be endangered.
''Macrobdella decora'' is found in North America east of the Rocky Mountains: in southern Canada and the neighbouring parts of the United States. There is, however, one disjunct population of leeches living in northern Mexico. The species may be able to mix and breed randomly across most of its range, but further research into the topic is needed. The saliva of ''M. decora'' contains a blood thinner dubbed "decorsin" which may be unique to the species. A comparison of the saliva of ''M. decora'' and that of European species has led researchers to the conclusion that blood-sucking in jawed leeches likely evolved from a single origin.
== Taxonomy == ''Macrobdella decora'' was originally placed in the genus ''Hirudo'' by Thomas Say, who described it in 1824 in an appendix to a book about an expedition up the Minnesota River. Three other species were described in the same pages: ''Placobdella parasitica,'' ''Nephelis lateralis'', and ''Haemopis marmorata''. Besides a brief physical description, Say noted that the species was "much smaller" than the other leeches he had described and was "comparatively rare."<ref name="Keating, 1824" /> When Addison Emery Verrill erected the genus ''Macrobdella'' in 1872, he transferred Say's species into it.<ref name="Verrill, 1872" />{{Rp|page=138}} ''Macro'' simply means 'big', while ''bdella'' means 'leech' in Greek.<ref name="de Jesus, 2019" /> It is commonly known as the North American medicinal leech.<ref name="McClure et al. 2021" />{{Reference page|page=2}}
''Macrobdella decora'' is most closely related (the sister taxon) to ''Macrobdella diplotertia.'' ''Macrobdella ditreta'' was previously believed to be sister to the clade comprising ''decora'' and ''diplotertia'', but a new species, ''Macrobdella mimicus'', was discovered in 2019 and placed as the sister taxon to that clade.<ref name="Phillips et al., 2019" />{{Rp|page=587}}<ref name=":0">{{Cite journal |last1=Phillips |first1=Anna J. |author-link1=Anna J. Phillips |last2=Siddall |first2=Mark E. |author-link2=Mark Siddall |date=2005 |title=Phylogeny of the New World medicinal leech family Macrobdellidae (Oligochaeta: Hirudinida: Arhynchobdellida) |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1463-6409.2005.00210.x |journal=Zoologica Scripta |language=en |volume=34 |issue=6 |pages=559–564 |doi=10.1111/j.1463-6409.2005.00210.x |issn=0300-3256 |url-access=subscription}}</ref>{{Rp|page=563}} The genus ''Macrobdella'' was formerly believed to be a monophyletic grouping,<ref name=":0" />{{Reference page|page=559}} but the 2019 paper that described ''M. mimicus'' concluded that ''Macrobdella'' was in fact a paraphyletic taxon. ''Macrobdella decora'', ''M. diplotertia'', and ''M. mimicus'' form one monophyletic clade. However, ''Macrobdella ditreta'' is more distantly related, and the grouping ''Macrobdella'' is paraphyletic as it excludes the monophyletic ''Philobdella'' clade. The 2019 researchers, led by Anna J. Phillips, used both maximum likelihood and maximum parsimony techniques to work out the phylogeny of the Macrobdellidae, and the techniques yielded slightly different results, with parsimony supporting the genus ''Philobdella'' as sister to the ''decora'', ''diplotertia'', and ''mimicus'' clade and the maximum likelihood analysis putting it sister to ''M. ditreta''.<ref name="Phillips et al., 2019" />{{Reference page|page=594}} {| style="margin: auto; border: none;" |{{cladogram|title=Parsimony analysis |cladogram= {{clade |label1=Macrobdellidae |1= {{clade |1=''Oxyptychus'' |2= {{clade |1=''M. ditreta'' |2= {{clade |1=''Philobdella'' |2= {{clade |1={{clade |1= {{clade |1='''''M. decora''''' |2=''M. diplotertia'' }} |2=''M. mimicus'' }} }} }} }} }} }} |align=center|caption=After Phillips et al., 2019.<ref name="Phillips et al., 2019" />{{Rp|page=594}}}} |{{cladogram|title=Maximum-likelihood analysis |cladogram= {{cladeR |reverse=yes |label1=Macrobdellidae |1= {{cladeR |1=''Oxyptychus'' |2= {{cladeR |1= {{cladeR |1=''M. ditreta'' |2=''Philobdella'' }} |2={{cladeR |1= {{cladeR |1='''''M. decora''''' |2=''M. diplotertia'' }} |2=''M. mimicus'' }} }} }} }} |align=center|caption=After Phillips et al., 2019.<ref name="Phillips et al., 2019" />{{Rp|page=594}}}} |- |} == Description == alt=A half-submerged leech with dark, olive-green back with rows of black and orange spots|thumb|Individual in Maine, with orange mid-line and black side spots all visible''Macrobdella decora'' is a medium-sized leech, growing between {{Convert|5 and 8.5|cm|in|abbr=on}} long, and weighing from {{Convert|1.5 to 3.7|g|oz}}, based on six specimens.<ref name="Phillips & Goetz, 2023">{{Cite journal |last1=Phillips |first1=Anna J. |last2=Goetz |first2=Freya E. |year=2023 |title=Comparative reproductive morphology of two species of ''Macrobdella'' (Hirudinea: Arhynchobdellida: Macrobdellidae) |url=https://link.springer.com/10.1007/s00435-023-00596-6 |journal=Zoomorphology |language=en |volume=142 |issue=2 |pages=153–168 |doi=10.1007/s00435-023-00596-6 |issn=0720-213X |url-access=subscription}}</ref>{{Rp|page=155}} It has a dark green, brown or olive-green back with a line of 20 or so small orange or red dots down the middle, and two corresponding sets of black dots on its sides. Its underbelly is reddish or orange with black spots dispersed irregularly across it.<ref name="Sawyer, 1972" />{{Rp|page=67}}<ref name="Keating, 1824" /><ref>{{Cite book |last1=Govedich |first1=Fredric R. |title=Ecology and Classification of North American Freshwater Invertebrates |last2=Bain |first2=Bonnie A. |last3=Moser |first3=William A. |last4=Gelder |first4=Stuart R. |last5=Davies |first5=Ronald W. |last6=Brinkhurst |first6=Ralph O. |date=2001 |publisher=Elsevier |isbn=978-0-12-690647-9 |chapter=Annelida (Clitellata): Oligochaeta, Branchiobdellida, Hirudinida, and Acanthobdellida |display-authors=2 |chapter-url=https://www.researchgate.net/publication/279971391}}</ref><ref name="Brooks, 1882">{{Cite book |last=Brooks |first=William Keith |author-link=William Keith Brooks |url=https://www.biodiversitylibrary.org/page/1011351#page/174/mode/1up |title=Handbook of invertebrate zoology. For laboratories and seaside work |date=1882 |publisher=S. E. Cassino |location=Boston}}</ref>{{Rp|page=160}} Its back is rounded but its belly is flattened.<ref name="Brooks, 1882" />{{Rp|page=160}}<ref name="Leidy, 1868">{{Cite book |last=Leidy |first=Joseph |author-link=Joseph Leidy |url=https://www.biodiversitylibrary.org/page/9768378#page/238/mode/1up |title=Proceedings of the Academy of Natural Sciences of Philadelphia |date=1868 |publisher=Academy of Natural Sciences of Philadelphia |volume=20 |location=Philadelphia |page=230 |chapter=Notice of some American Leeches |access-date=2024-11-30 |archive-url=https://web.archive.org/web/20220120155733/https://www.biodiversitylibrary.org/page/9768378#page/238/mode/1up |archive-date=2022-01-20 |url-status=live}}</ref>{{Rp|page=230}} All leech species have 32 segments, but these divisions are obscured by numerous external ring markings called annuli;<ref name="Kuo & Lai, 2018" /> ''M. decora'' has "from 90 to 94 annuli" in total.<ref name="Leidy, 1868" />
=== Anatomy === The head of ''M. decora'' is rounded and has ten simple eyes on the front of its body: one pair between segments two and three; a second pair on segment three; a third on four; a fourth on six; and a fifth and final pair on segment nine.<ref name="Verrill, 1872" />{{Rp|page=138}} They are arranged in the shape of a horseshoe.<ref name="Brooks, 1882" />{{Rp|page=160}}<ref name="Leidy, 1868" /> The nervous system includes twenty-one neuron clusters<ref>{{Cite book |url=https://books.google.com/books?id=zCLLDwAAQBAJ&dq=%22ganglia%22+%22glossary:&pg=PA192 |title=Encyclopedia of Gastroenterology |date=2019-11-06 |publisher=Academic Press |isbn=978-0-12-818728-9 |language=en}}</ref> called ganglia and a nervous cord running the length of the body, comprising two parallel fibres enclosed for most of their length in one sheath. The first and last of the ganglia are larger than the others, and connect to five and seven nerves respectively, whereas the other nineteen connect to four or fewer nerves each. The brain is located above the pharynx. The brain is two-parted, with each half connecting to the five ocelli on that side of the body with corresponding optic nerves.<ref name="Brooks, 1882" />{{Rp|page=|pages=166–7}} Leech jaws are chitinous blades with sharp, serrated edges.<ref>{{Cite book |last1=Raven |first1=Peter |url=https://books.google.com/books?id=CoZvEAAAQBAJ |title=EBOOK: Biology |last2=Johnson |first2=George |last3=Mason |first3=Kenneth |last4=Losos |first4=Jonathan |last5=Singer |first5=Susan |date=2013-02-16 |publisher=McGraw Hill |isbn=978-0-07-715722-7 |language=en}}</ref> ''Macrobdella decora'' has three long jaws which are semicircular and laterally compressed, each with one row of about sixty-five "extremely sharp" teeth.<ref name="Leidy, 1868" /><ref name="Moore, 1901">{{Cite journal |last=Moore |first=J. Percy |author-link=John Percy Moore |date=Feb 1901 |title=The Hirudinea of Illinois |url=https://iopn.library.illinois.edu/journals/inhs/article/view/423/353 |url-status=live |journal=Bulletin of the Illinois State Laboratory of Natural History |volume=5 |archive-url=https://web.archive.org/web/20241202222708/https://iopn.library.illinois.edu/journals/inhs/article/view/423/353 |archive-date=2024-12-02 |access-date=2024-11-30}}</ref><ref name="Sawyer, 1972" />{{Rp|page=67}} Each jaw uses a saw-like motion to cut open its victim's skin.<ref>{{Cite web |title=Triple Jaw Leech |url=https://www.amnh.org/research/microscopy-and-imaging-facility/instruments/hitachi-s-4700/hitachi-images/triple-jaw-leech |url-status=deviated |archive-url=https://web.archive.org/web/20250217012249/https://www.amnh.org/research/microscopy-and-imaging-facility/instruments/hitachi-s-4700/hitachi-images/triple-jaw-leech |archive-date=17 Feb 2025 |website=American Museum of Natural History}}</ref>
''M. decora'' has a large muscular pharynx which accounts for the first tenth of the leech's digestive tract. The stomach is not nearly as muscular as the pharynx, but it occupies about five sixths of the leech's total body length and is subdivided into eleven chambers. The intestine extends from behind the stomach and narrows towards the anus. The last part of the intestine is the colon, followed finally by a small rectum.<ref name="Brooks, 1882" />{{Rp|page=163–5}} The anus is located on the leech's back, above its circular acetabulum,<ref name="Leidy, 1868" /> a large posterior sucker.<ref>{{Cite journal |last1=Panyarachun |first1=Busaba |last2=Ngamniyom |first2=Arin |last3=Sobhon |first3=Prasert |last4=Anuracpreeda |first4=Panat |display-authors=2 |date=2013 |title=Morphology and histology of the adult Paramphistomum gracile Fischoeder, 1901 |journal=Journal of Veterinary Science |volume=14 |issue=4 |pages=425–432 |doi=10.4142/jvs.2013.14.4.425 |issn=1976-555X |pmc=3885736 |pmid=23820216}}</ref>
Nephridia are understood to be the primary organs handling the balance between salt and water in leeches. A 1987 study examined how ''M. decora'' withstood osmotic shock (a shock caused by sudden alteration in the concentration of a given solute, resulting in dehydration via osmosis<ref>{{Cite book |last1=Lund-Hansen |first1=Lars Chresten |url=https://books.google.com/books?id=MUD2DwAAQBAJ&dq=%22osmotic+shock%22+%22glossary%22&pg=PA176 |title=Arctic Sea Ice Ecology: Seasonal Dynamics in Algal and Bacterial Productivity |last2=Søgaard |first2=Dorte Haubjerg |last3=Sorrell |first3=Brian Keith |last4=Gradinger |first4=Rolf |last5=Meiners |first5=Klaus Martin |date=2020-08-07 |publisher=Springer Nature |isbn=978-3-030-37472-3 |page=176 |language=en}}</ref>) and found that the nephridia could not tolerate hypertonicity (overly salty solutions), and, when compared with the European ''Hirudo medicinalis'', the North American species was relatively inefficient at the swift removal of surplus water and salt.<ref>{{Cite journal |last=Wenning |first=Angela |date=1987-09-01 |title=Salt and Water Regulation in <i>Macrobdella Decora</i> (Hirudinea: Gnathobdelliformes) Under Osmotic Stress* |url=https://doi.org/10.1242/jeb.131.1.337 |journal=Journal of Experimental Biology |volume=131 |issue=1 |pages=337–349 |doi=10.1242/jeb.131.1.337 |bibcode=1987JExpB.131..337W |issn=0022-0949|url-access=subscription }}</ref>{{Rp|page=337}}
==== Reproductive anatomy ==== {{See also|Leech#Reproduction and development}} [[File:North American Medicinal Leech imported from iNaturalist photo 56392667 on 4 December 2022.jpg|thumb|An individual from Buckingham, Quebec|alt=A fat, black leech with a line of small orange spots down its back]] All leeches are hermaphrodites whose male reproductive organs mature first and the female ones later.<ref name="Ruppert477">{{cite book |last1=Ruppert |first1=Edward E. |title=Invertebrate Zoology, 7th Edition |last2=Fox |first2=Richard S. |last3=Barnes |first3=Robert D. |publisher=Cengage Learning |year=2004 |isbn=978-81-315-0104-7 |pages=477–8}}</ref> Testisacs are separate sperm-producing parts of the main body cavity; similarly, ovisacs are parts of the cavity which contain tissues specialized for oogenesis. The ovisacs connect to the leech vagina via oviducts, while epididymes connect the vas deferens with the ejaculatory ducts.<ref>{{Cite book |last=Utevsky |first=Andrei |url=https://archive.org/details/bonner-zoologische-monographien-54-0001-0080/page/n3/mode/2up?q=%22Antarctic+Piscicolid+Leeches%22 |title=Antarctic Piscicolid leeches |year=2007 |pages=7–8 |chapter=Glossary of special terms}}</ref>''<ref name="Moore, 1901" />{{Rp|page=510}} M. decora'' has ten pairs of testisacs located from segments thirteen to twenty-three, with large, compact, and much-coiled epididymes, and crescent-shaped or globular ovisacs which are located in the thirteenth segment. A 2023 paper described the leech's oviducts as "thin" and "torturously folded".<ref name="Phillips & Goetz, 2023" />{{Rp|page=155}}<ref name="Moore, 1901" />{{Rp|page=510}} The male and female gonopores, which are external openings to the internal reproductive organs,<ref>{{Cite web |title=gonopore |url=https://www.oxfordreference.com/display/10.1093/oi/authority.20110803095859225 |access-date=2025-01-04 |website=Oxford Reference |language=en }}</ref><ref>{{Cite web |title=Crustacea Glossary::Definitions |url=https://research.nhm.org/glossary/define.html?term=Gonopore |access-date=2025-01-04 |website=research.nhm.org}}</ref> are usually separated by five annuli, or external rings; this degree of separation is an important feature for identifying the species.<ref name="Sawyer & Pass, 1972">{{Cite journal |last1=Sawyer |first1=Roy T. |last2=Pass |first2=K. A. |date=1972 |title=The occurrence of ''Macrobdella decora'' (Say, 1824) (Annelida: Hirudinea) in the Appalachian Mountains of Georgia and South Carolina |journal=Journal of the Elisha Mitchell Scientific Society |volume=88 |issue=1 |pages=34–5 |jstor=24334685}}</ref><ref name="Sawyer, 1972" />{{Rp|page=67}} The male gonopore, when withdrawn, appears as nothing more than a hole in between segments eleven and twelve; however, when the male gonopore and its surrounding parts are everted, they appear as a small cone with deeply furrowed sides, the organ being at the tip. The leech's four copulatory glands are arrayed in a square in an area of rough skin on segments thirteen and fourteen.<ref name="Moore, 1901" />{{Rp|page=509}}
=== Saliva === Leech saliva is known to contain several compounds, including hirudin, an anticoagulant.<ref>{{Cite journal |author-link=John Berry Haycraft |year=1883 |title=IV. On the action of a secretion obtained from the medicinal leech on the coagulation of the blood |journal=Proceedings of the Royal Society of London |volume=36 |issue=228–231 |pages=478–487 |doi=10.1098/rspl.1883.0135 |doi-access=free |author-last=Haycraft |author-first=John B.}}</ref><ref name="Min et al., 2010">{{Cite journal |last1=Min |first1=Gi-Sik |last2=Sarkar |first2=Indra Neil |last3=Siddall |first3=Mark E. |year=2010 |title=Salivary Transcriptome of the North American Medicinal Leech, ''Macrobdella decora'' |url=http://www.bioone.org/doi/abs/10.1645/GE-2496.1 |journal=Journal of Parasitology |language=en |volume=96 |issue=6 |pages=1211–1221 |doi=10.1645/GE-2496.1 |issn=0022-3395 |pmid=21158638}}</ref> The saliva of ''M. decora'' is also known to contain several substances not previously all identified from the same leech, as well as an anticoagulant dubbed decorsin which might be unique to ''M. decora''. The set of all mRNA expressed in ''M. decora'' saliva (its transcriptome) was described in 2010.<ref name="Min et al., 2010" /><ref>{{Cite web |title=transcriptome {{!}} World Library of Science |url=https://www.nature.com/wls/definition/transcriptome-296/ |access-date=2025-08-09 |website=www.nature.com}}</ref><ref>{{Cite web |title=Transcriptome |url=https://genomequebec.com/en/glossary/transcriptome/ |access-date=2025-08-09 |website=Genome Québec |language=en-US}}</ref> A 2019 paper published in the ''Journal of Parasitology'' compared hirudin and decorsin from ''M. decora'', as well as hirudin and "hirudin-like factors" – substances which resemble hirudin but are not known to act as anticoagulants – obtained from European species. The authors concluded that blood-sucking among jawed leeches evolved from a single origin.<ref>{{Cite journal |last1=Müller |first1=Christian |last2=Lukas |first2=Phil |last3=Lemke |first3=Sarah |last4=Hildebrandt |first4=Jan-Peter |date=2019-06-04 |title=Hirudin and Decorsins of the North American Medicinal Leech Macrobdella decora: Gene Structure Reveals Homology to Hirudins and Hirudin-Like Factors of Eurasian Medicinal Leeches |url=https://bioone.org/journals/journal-of-parasitology/volume-105/issue-3/18-117/Hirudin-and-Decorsins-of-the-North-American-Medicinal-Leech-Macrobdella/10.1645/18-117.full |journal=Journal of Parasitology |volume=105 |issue=3 |pages=423–431 |doi=10.1645/18-117 |issn=0022-3395 |pmid=31163003 |url-access=subscription}}</ref>{{Rp|pages=423–4}}
== Ecology ==
=== Distribution and habitat === ''Macrobdella decora'' is the most widely distributed ''Macrobdella'' species, and it is found in North America east of the Rocky Mountains in southern Canada and the neighbouring United States. There is, however, one isolated population in Mexico, in the state of Nuevo León.<ref name="Phillips et al., 2019">{{Cite journal |last1=Phillips |first1=Anna J. |last2=Salas-Montiel |first2=Ricardo |last3=Kvist |first3=Sebastian |last4=Oceguera-Figueroa |first4=Alejandro |date=2019-08-15 |title=Phylogenetic Position and Description of a New Species of Medicinal Leech from the Eastern United States |journal=Journal of Parasitology |volume=105 |issue=4 |pages=587–597 |doi=10.1645/18-119 |issn=0022-3395 |pmid=31414949 |doi-access=free}}</ref>{{Rp|page=587}} For the most part, ''M. decora'' does not occur south of Virginia, ''Macrobdella ditreta'' being the dominant leech species in the southern United States. However, ''M. decora'' has been found in the southern Appalachian Mountains in Georgia and South Carolina.<ref name="Sawyer & Pass, 1972" /> Leeches of the species have been found as far west as Alberta, North Dakota, Nebraska, Colorado, and New Mexico.<ref name="Kennedy et al., 2024">{{Cite journal |last1=Kennedy |first1=Nat |last2=Kvist |first2=Sebastian |last3=Oceguera-Figueroa |first3=Alejandro |last4=Phillips |first4=Anna J. |last5=Stacey |first5=Donald F. |last6=de Carle |first6=Danielle |date=2024-09-03 |title=A phylogeographic analysis of the North American medicinal leech, ''Macrobdella decora'' (Say, 1824) |journal=Zoologica Scripta |language=en |volume=54 |pages=103–118 |doi=10.1111/zsc.12692 |issn=0300-3256 |doi-access=free}}</ref> At the eastern end of their range, they are also found on Prince Edward Island.<ref name="Sawyer, 1972" />{{Rp|page=68}} ''M. decora'' is possibly panmictic (i.e., mixing and breeding randomly<ref>{{Cite web |title=Definition of PANMIXIA |url=https://www.merriam-webster.com/dictionary/panmixia |access-date=2025-01-04 |website=www.merriam-webster.com |language=en}}</ref>) across much of its range. Some populations in Ontario and New England have refrained from panmixia, and, furthermore, a 2024 paper that studied the geographic distribution of the species' genetic diversity<ref>{{Cite book |last=Avise |first=John C. |url=https://books.google.com/books?id=lA7YWH4M8FUC&q=phylogeography |title=Phylogeography: The History and Formation of Species |date=2000-01-03 |publisher=Harvard University Press |isbn=978-0-674-66638-2 |language=en}}</ref> (phylogeography) concluded that it should not be assumed "that ''M. decora'' is truly panmictic" across the study's large range, and that more research into the topic was needed.<ref name="Kennedy et al., 2024" />
''Macrobdella decora'' is a freshwater species that is found in still or slow-moving water bodies such as streams, temporary ponds, ditches, and wetlands.<ref name="Sawyer, 1972" />{{Rp|page=67}}<ref name="de Jesus, 2019" /><ref name="Lloyd Center" /> They are particularly common in temporary ponds; the leeches are able to burrow into the bottom when the pond dries up.<ref>{{Cite book |last=Sawyer |first=Roy T. |url=https://archive.org/details/leechbiologybeha0000sawy/mode/2up?q=decora |title=Leech biology and behaviour |date=1986 |publisher=Clarendon Press, Oxford University Press |others=Internet Archive |isbn=978-0-19-857377-7}}</ref>{{Rp|page=417}} They are able to survive some time on land, and have been found up to {{Convert|30|m}} away from aquariums in which they were kept. They may also attach to a terrestrial host such as a mammal or bird and follow the host onto shore. Nonetheless, their overland biological dispersal ability "is assumed to be limited".<ref name="Kennedy et al., 2024" />{{Reference page|page=105}} In lakes, the leeches are most active in the epilimnion, or top-most layer.<ref>{{Cite journal |last1=Canfield |first1=Samuel |last2=Crowl |first2=Todd |last3=Bahleda |first3=Kristin |date=2017-04-04 |title=''Bellamya chinensis'' and ''Lymnaea stagnalis'' mortality in the presence of ''Macrobdella decora'' |journal=Proceedings of the West Virginia Academy of Science |volume=89 |issue=1 |doi=10.55632/pwvas.v89i1.254 |issn=2473-0386|doi-access=free }}</ref>{{Rp|page=3}}
NatureServe lists the species as Secure within Ontario, but no assessment has been completed for other regions.<ref name="NS" /> ''M. decora'' was described as unendangered in a 2021 paper on its gut microbiome.<ref name="McClure et al. 2021" />{{Rp|page=1}} As of October 2025, ''M. decora'' was the most-observed species of leech in Canada on the citizen science platform iNaturalist, and the second-most-observed species in the United States, after ''Placobdella parasitica''.<ref>{{Cite web |title=Observations (Canada) |url=https://www.inaturalist.org/observations?place_id=6712&subview=map&taxon_id=63081&view=species |access-date=2025-08-02 |website=iNaturalist |language=en}}</ref><ref>{{Cite web |title=Observations (United States) |url=https://www.inaturalist.org/observations?place_id=1&subview=map&taxon_id=63081&view=species |access-date=2025-08-02 |website=iNaturalist |language=en}}</ref> [[File:North American Medicinal Leech, Tolland, Connecticut, United States imported from iNaturalist photo 785245.jpg|alt=An underwater photograph of a leech swimming through a cloud of small, black frog's eggs|thumb|An individual swimming through a cloud of wood frog eggs in Connecticut]]
=== Parasitism and diet === ''Macrobdella decora'' is both parasitic and predaceous. Using its teeth to pierce the host's skin, it sucks the blood of many vertebrates, including humans but also amphibians, fish, turtles, wading birds, and cattle.<ref name="Sawyer, 1972" />{{Rp|pages=67–8}} The leech can remain attached to its host for up to two hours.<ref name="Kennedy et al., 2024" />{{Reference page|page=105}} It also hunts voraciously, and eats oligochaete worms, snails, amphibian eggs, the larvae of insects, and even other individuals of its own species. In the spring, the leech's aggressive predation of American toad eggs may lead to up to 80% mortality.<ref name="Sawyer, 1972" />{{Rp|pages=67–8}} The leeches have also been recorded hunting amphibian larvae: in 2020, a leech was found preying on tiger salamander larvae in Minnesota.<ref>{{Cite journal |last1=Seymour |first1=Alexander M. |last2=Lamb |first2=Jennifer Y. |date=2020 |title=Natural History Notes |url=https://www.researchgate.net/publication/352101325 |journal=Herpetological Review |volume=51 |issue=2 |pages=288}}</ref> However, ''M. decora'' is also preyed on by ''Haemopis grandis'', a predator and scavenger leech.<ref name="Sawyer, 1972" />{{Rp|page=62}} The leeches are also themselves parasitized by trematodes, a new species of which, ''Alloglossidum hamrumi'', was described from the intestine of a specimen of ''M. decora'' in 1976.<ref>{{Cite journal |last1=Neumann |first1=Mary P. |last2=Vusse |first2=Frederick J. V. |date=Aug 1976 |title=Two new species of ''Alloglossidium'' Simer 1929 (Trematoda: Macroderoididae) from Minnesota leeches |journal=The Journal of Parasitology |volume=62 |issue=4 |pages=556–9 |doi=10.2307/3279414 |jstor=3279414}}</ref>
=== Reproduction === The leeches engorge themselves with blood before mating. One or two months after feeding, they produce spongy cocoons, which are pale yellow and elliptical in shape. About another month later, the young, only {{Convert|20 to 22|mm|in}} long, emerge.<ref name="Sawyer, 1972" />{{Rp|page=68}} They will take several years to become fully mature.<ref>{{Cite thesis |publisher=Louisiana State University and Agricultural and Mechanical College |degree=PhD |last=Beckerdite |first=Fred Willie |title=The Description and Life History of a New Species of Alloglossidium (Trematoda: Macroderoididae).Alloglossidium (Trematoda: Macroderoididae). |url=https://repository.lsu.edu/cgi/viewcontent.cgi?article=3444&context=gradschool_disstheses |journal= |archive-date=2024-07-19 |access-date=2024-12-20 |archive-url=https://web.archive.org/web/20240719141444/https://repository.lsu.edu/cgi/viewcontent.cgi?article=3444&context=gradschool_disstheses |url-status=live }}</ref>
=== Gut microbiome === The gut microbiome is simply the collection of microorganisms living in an animal's digestive system.<ref>{{Cite book |last1=Ishiguro |first1=Edward |url=https://books.google.com/books?id=pi2gEAAAQBAJ&q=what+is+a+gut+microbiome |title=Gut Microbiota: Interactive Effects on Nutrition and Health |last2=Haskey |first2=Natasha |last3=Campbell |first3=Kristina |date=2023-06-22 |publisher=Elsevier |isbn=978-0-323-91389-8 |language=en}}</ref> The gut microbiome of the North American ''Macrobdella decora'' is quite similar to that of Europe's ''Hirudo verbana.'' Bacteria of the genera ''Aeromonas'', ''Bacteroides'', ''Butyricicoccus'', and ''Proteocatella'' dominate ''M. decora''{{'}}s gut microbiota.<ref name="McClure et al. 2021">{{Cite journal |last1=McClure |first1=Emily Ann |last2=Nelson |first2=Michael C. |last3=Lin |first3=Amy |last4=Graf |first4=Joerg |date=2021-04-27 |editor-last=Johnson |editor-first=Karyn N. |title=''Macrobdella decora'': Old World Leech Gut Microbial Community Structure Conserved in a New World Leech |journal=Applied and Environmental Microbiology |language=en |volume=87 |issue=10 |article-number=e02082-20 |bibcode=2021ApEnM..87E2082M |doi=10.1128/AEM.02082-20 |issn=0099-2240 |pmc=8117757 |pmid=33674439}}</ref>{{Rp|page=1}} The intraluminal fluid – that is, fluids found in the gut<ref>{{Citation |last=Skolnick |first=M. Leon |title=Intra- and Extraluminal Fluid |date=1981 |work=Real-time Ultrasound Imaging in the Abdomen |pages=191–212 |editor-last=Skolnick |editor-first=M. Leon |url=https://link.springer.com/chapter/10.1007/978-1-4612-5919-0_9 |access-date=2025-01-01 |archive-url=https://web.archive.org/web/20250101150528/https://link.springer.com/chapter/10.1007/978-1-4612-5919-0_9 |archive-date=2025-01-01 |url-status=live |place=New York, NY |publisher=Springer |language=en |doi=10.1007/978-1-4612-5919-0_9 |isbn=978-1-4612-5919-0 |url-access=subscription}}</ref> – was found to be most abundant with bacteria like ''Aeromonas'' and ''Bacteroidales''; combined, on median they represented 60% of microbiota living in the fluids, while much of the rest was ''Clostridiales'', which on median accounted for 30% of the microbiota.<ref name="McClure et al. 2021" />{{Rp|page=5}} [[File:North American Medicinal Leech, Algonquin Provincial Park, Algonquin Highlands, ON, CA imported from iNaturalist photo 88700087.jpg|thumb|right|''M. decora'' on a human hand in Algonquin Provincial Park]]
== Interactions with humans == ''Macrobdella decora'' may parasitize humans and is often encountered by people swimming in Canada and the northern United States. Sometimes swimming areas have had to be restricted or closed due to the leech's presence.<ref name="Sawyer, 1972" />{{Rp|page=67}} In Europe, ''Hirudo medicinalis'' was traditionally used for bloodletting.<ref>{{Cite book |last1=Kirk |first1=Robert G. W. |url=https://books.google.com/books?id=wcy3Wb27iEEC&dq=%22leech%22+%22bloodletting%22&pg=PA52 |title=Leech |last2=Pemberton |first2=Neil |date=2013-02-15 |publisher=Reaktion Books |isbn=978-1-78023-068-9 |page=46 |language=en}}</ref> Despite its common name as a "medicinal leech", ''M. decora'' was historically not used very often for this purpose.<ref name="McClure et al. 2021" />{{Rp|page=2}} However, there is some evidence of their medicinal use as a replacement to European leeches, specifically in Philadelphia during the 19th century.<ref name="Kennedy et al., 2024" /> Indeed, Addison Emery Verrill, writing in 1872, noted ''M. decora''{{'}}s use by doctors as a stand-in for "imported leeches", and he noted the North American species was "equally efficacious".<ref name="Verrill, 1872" />{{Rp|page=132}} It is possible that human leech-trading helped move leeches between water bodies. According to a 2024 paper, they are sometimes used by fishers for fishing bait, and they may be transported for that reason. However, they are not a preferred choice, due to a tendency to get free of collection traps. Fish are also claimed anecdotally by fishers to find them less attractive than other leech species.<ref name="Kennedy et al., 2024" />{{Reference page|page=115}}
== References == <references>
<ref name="Sawyer, 1972">{{Cite journal |last=Sawyer |first=Roy T. |date=1972 |title=North American freshwater leeches, exclusive of the Piscicolidae, with a key to all species |url=https://www.biodiversitylibrary.org/item/114451 |url-status=live |journal=Illinois Biological Monographs |location=Urbana |publisher=University of Illinois Press |volume=46 |doi=10.5962/bhl.title.53881 |hdl=2142/27340 |isbn=0-252-00214-8 |oclc=304005 |archive-url=https://web.archive.org/web/20170319234056/http://www.biodiversitylibrary.org/item/114451 |archive-date=2017-03-19 |access-date=2024-11-29 |hdl-access=free}}</ref>
<ref name="de Jesus, 2019">{{Cite web |last=Garcia de Jesus |first=Erin I. |title=This Smithsonian Scientist is on a Mission to Make Leeches Less Scary |url=https://www.smithsonianmag.com/blogs/national-museum-of-natural-history/2019/08/23/smithsonian-scientist-mission-make-leeches-less-scary/ |url-status=live |archive-url=https://web.archive.org/web/20241130090030/https://www.smithsonianmag.com/blogs/national-museum-of-natural-history/2019/08/23/smithsonian-scientist-mission-make-leeches-less-scary/ |archive-date=2024-11-30 |access-date=2024-11-29 |website=Smithsonian Magazine |language=en}}</ref>
<ref name="Lloyd Center">{{Cite web |title=Freshwater leech (''Macrobdella decora'') |institution=Lloyd Center for the Environment |location=Dartmouth, Massachusetts |url=https://lloydcenter.org/freshwater-leech-macrobdella-decora/ |access-date=2024-11-29 |language=en-US}}</ref>
<ref name="NS">{{Cite NatureServe|id=2.841852|title=''Macrobdella decora''}}</ref>
<ref name="Kuo & Lai, 2018">{{Cite journal |last1=Kuo |first1=Dian-Han |last2=Lai |first2=Yi-Te |date=4 November 2018 |title=On the origin of leeches by evolution of development |journal=Development, Growth & Differentiation |volume=61 |issue=1 |pages=43–57 |doi=10.1111/dgd.12573 |pmid=30393850 |s2cid=53218704 |quote=and a fixed number (32) of segments |doi-access=free}}</ref>
<ref name="Keating, 1824">{{Cite book |last1=Keating |first1=William Hypolitus |author-link1=William H. Keating |url=https://www.biodiversitylibrary.org/page/13640684#page/296/mode/1up |title=Narrative of an expedition to the source of St. Peter's river, Lake Winnepeek, Lake of the Woods, &c., performed in the year 1823, ... under the command of Stephen H. Long |last2=Long |first2=Stephen H. |author-link2=Stephen H. Long |last3=von Schweinitz |first3=Lewis David |author-link3=Lewis David de Schweinitz |date=1824 |publisher=H. C. Carey & I. Lea |volume=2 |location=Philadelphia |page=268}}</ref>
<ref name="Verrill, 1872">{{Cite journal |last=Verrill |first=A. E. |author-link=Addison Emery Verrill |year=1872 |editor-last=Dana |editor-first=James D. |editor-link=James Dwight Dana |editor2-last=Silliman |editor2-first=Benjamin |editor2-link=Benjamin Silliman Jr. |title=Brief Contributions to Zoölogy from the Museum of Yale College. No. XVII.—Descriptions of North American fresh-water Leeches |url=https://www.biodiversitylibrary.org/page/36995314#page/147/mode/1up |url-status=live |journal=The American Journal of Science and Arts |series=Third series |location=New-Haven |publisher=S. Converse |volume=3 |page=126–139 [137] |archive-url=https://web.archive.org/web/20231108042842/https://www.biodiversitylibrary.org/page/36995314#page/8/mode/1up |archive-date=2023-11-08 |access-date=2024-11-29}}</ref>
</references>
== External links == *{{cci|Macrobdella decora}}
{{Taxonbar|from=Q5166955}}
Category:Arhynchobdellida Category:Freshwater animals of North America Category:Invertebrates of North America Category:Animals described in 1824 Category:Taxa named by Thomas Say