Our good friend, the leach

                                                                                     Erpobdella punctata

 

Leeches more than just bait

 

Leeches, live and imitation (such as the egg-sucking leech fly pattern for Salmon/Steelhead above), are probably the single best all-round bait for freshwater gamefish, including trout. They are important in the food web of a lake or aquatic ecosystem acting both as predators, prey, and parasites.

The vast majority of the world's 650 species of leeches are found in cool freshwater, shallow lakes, ponds and back waters of rivers and creeks of North America and Europe. Leeches can also be found attached to the underside of submerged stones, logs or in organic pond sediment or concealed among aquatic plants -- especially the underside of pond rushes.

Leeches spend the winter buried in mud just below the frost line. All leech species are carnivorous and have evolved from detritus-eating earthworms. Some are predatory, feeding on a variety of invertebrates such as worms, snails, insect larvae, crustaceans, while a very few are parasitic, blood-sucking leeches feeding on the blood of vertebrates such as amphibians, waterfowl, reptiles and fish. Given the opportunity, they will also feed on human blood. The most important predators on leeches are fish, aquatic insects, crayfish and other leeches specialized for predation on leeches.

After some sleuthing, I learned the name of the leech sold in my local bait shop and was I surprised: Bait leech. Its scientific name is Nephelopsis obscura, but because of its worm-like crawling behavior -- vermiform -- on a solid surface it is commonly called a worm-leech. It is taxonomically classified within the "Order" of "jawed" leeches (Arhynchobdellida), and sub-order "jaws unarmed with teeth."

The worm-leeches consist of freshwater or amphibious leeches that have lost the ability to penetrate a host's tissue and suck blood. These leeches are carnivorous and are equipped with a relatively large mouth to ingest worms, or insect larvae, which are swallowed whole. N obscura, the bait leech, is very closely related to our common New York state worm-leech Erpobdella punctata, but adapted to colder, more northerly waters. The bait leech sold locally has been shipped from Minnesota or Wisconsin where it was trapped. Rod Fudge, for example, of Perham, Minn. -- with his crew of seven employees crouched in "john boats"  from midnight  until  8 a.m. all over northern Minnesota -- ships 15 tons of "fishing" leeches, all caught by hand, to bait shops across the country.

Jawed leeches, armed with hundreds of tiny sharp teeth, include the European medical leech, Hiruda medicinalis and its North American counterpart -- the much less efficient medical leech -- Macrobdella decora. H. medicinalis is an endangered species in Europe, but it is being commercially raised by Biopharm in Wales, UK for medical purposes, like reconnecting the blood capillaries of a severed finger, nose or body limb .

The second  "Order"  of leeches is the "jawless" leeches (Rhynchobdellida), armed with a muscular straw-like proboscis puncturing organ in a retractable sheath. A good example is Glossiphonia complanata -- the snail leech -- which sucks up the body fluids and soft parts from invertebrate prey organisms.

Helobdella (Glossiphonia) stagnalis is the most widely distributed leech in the world. It is a major predator on small benthic invertebrates, primarily oligochaetes (worms) and midges, and finds organically enriched (polluted) waters hospitable. It, together with E. punctata and its European counterpart E. octoculata, are considered pollution indicator species.

Leeches have exploited the sucker mode of locomotion, feeding and reproduction to an extreme.

The suckers are really suction cups at each end of the body that create a slight negative pressure, or vacuum suction, or secreting a viscous mucopolysaccharide adhesive glue for attachment to substrate or prey.

Leeches move by either a unique graceful yet  quick up-and-down swimming style; or by vermiform -- inchworm-- crawling using an exaggerated loop.

It is a curious fact that only the "jawed" leeches, which include worm-leeches, can swim. As a general rule the jawless leeches such as H. stagnalis can't swim under any circumstances, even though they live in an aquatic environment. When dropped into water they curl up into a ball and sink to the bottom.

 

More Leach info

The Leech and I

   By STANLEY SCHARF

 
The Finger Lakes Environmental Film Festival for 2003 screened a film, "The  Leech and the Earthworm" which took its title from a folktale, repeated in the film by Chief Viraleo ,  of the South Pacific (Oceania) Island nation of  Vanuato famous for giving the
world its native  yam harvest celebration of "bungee jumping."  It is  the story of a deadly lie: the leech convinces the earthworm
that life will be better if it would only come up out of the earth into the hot sunshine...
 

 Leeches and earthworms are ,indeed, closely related. They both belong to the animal phylum, Annelida, whose bodies are built of many joined segments or rings (annuli). Both are specialized worms of the group Clitellata, or "packsaddle" segmented worms comprising Oligochaeta (which includes the earthworm) and Hirudinea (leeches).

 
 Clitellates are hermaphradites,  characterized by the clitellum band of clitellar gland cells distinctly visible  on the skin of
earthworms but only becoming visible on leeches during maturation of the female reproductive system.  Fertilization is internal.. The
clitellum secretes the egg containing cocoon which slips off over the head to be deposited on substrates, attached to parent, or
contained in an internal brood pouch.
 
All clitellates are divided  into repeating units. In  Hirudinea the basic or primary number of annuli per body  segment is three.  The
total number of segments is a  constant 34;with 6 segments devote to the head. The constraint of a fixed number of segments prevents the leech from regenerating lost or damaged segments.. By contrast the earthworm can add an almost unlimited number of annuli as it grows and has the remarkable capacity for regenerating new segments.Unlike the earthworm the leech does not have internal walls separating its segments so a cavity is available as a fluid reservoir.
 
Leeches do have a number of features  which are more like those found in arthropods (insects)  than  in Oligochaetes. Salient among these are compound eyes and yolky eggs. Division of Clitellata into the two classes: Oligochaeta and Hirudinea reflects their diversity of feeding habits. The former feed on detritus  and other organic material present in soil whereas ALL leeches are carnivorous.  They are more advanced physiologically than their cousins the earthworm from whom they evolved. Their undulating locomotion in water, feeding, and reproduction is primarily achieved by means of suction cups, suckers, located at both ends of
the body.  The oral sucker which is on the ventral side of the leech head space is a specialized muscular and glandular disk.
 
 Of the 650 leech species worldwide some are marine, and a few terrestrial but the vast majority have found a niche and reach their
greatest abundance in cool-freshwater shallow lakes, ponds and backwaters of rivers and creeks of temperate North America and
Europe. Contrary to popular belief, the most common and widespread species of leech are predatory leeches which feed and prey upon invertebrates! In temperate regions ,at least, bloodsucking leeches constitute a very minor part of the leech fauna.
 
The quintessential leech, the European bloodsucking  medical leech, Hirudo medicinalis is today an endangered species all across Europe and  is, in fact, already extinct in Ireland.  However it is being commercially raised by Biopharm in Swansea, Wales, UK  for such unique uses as reconnecting limbs such as fingers. The  incision mark left on the skin by the  European medical leech is an inverted Y inside of a circle.... the insignia of Mercedes Benz.. The comparable but much less efficient North American bloodsucking leech is Macrobdella decora. The  *ultimate* leech bloodsucking-parasite of mammals is not the European leech , but the  buffalo leeches of Southeast  Asia...Its  jaw is larger and bear more teeth  enabling them, even as baby  hatchlings ,to pierce the tough hide of water buffalo and even ...elephants ...Imagine how USEFUL it could be against your enemies or not nice people!!
 
Medicinal leeches like Macrobdella decora in North America and Hirudo medicinalis in Europe normally feed on frogs and other
amphibians .. H. medicinalis represents an order (Arhynchobdellida) of "jawed" leeches. They have multiple jaws with several hundred tiny sharp teeth to cut through skin in order to withdraw blood. The bite is painless and usually not noticed because along with the bite is an injection of  leech  saliva containing a numbing anesthetic and anti-coagulant. The jawed leech , alone among leeches, is distinguished sexually by having a penis and a vagina..
 
The other  major order (Rhynchobdellida) of leeches is the "jawless" leeches  such as Glossiphonia complanata (the snail leech) which suck up the body fluid and soft parts from invertebrate prey organisms, etc, by means of a muscular straw-like proboscis
 
puncturing organ in a retractable sheath. (Helobdella Glossiphonia) stagnalis is the most widely distributed leech in the world.  In the
northern hemisphere it reaches its highest population density in eutrophic waters. It is a major predator on small benthic  invertebrates, primarily oligochaetes and cheronomids, and thus  finds organically enriched (polluted) waters hospitable. H.
stagnalis is 10-15 mm long,2-3 mm wide and is easily identified by the position of the brown scute-plate on the nape of its neck.  
Theromyzon tessulatum  has only a rudimentary proboscis to feed on the blood of aquatic birds through the thin membranes! of their nasal passages or gills or skin of fish (Piscicolidae).
 
Erpobdelliformes, or worm-leeches, belonging to the  order of jawed leeches,  consist of freshwater or amphibious leeches which have lost  the ability of penetrating the tissue of a host and sucking blood. These leeches are carnivorous and  come equipped with a relatively large mouth to ingest worms, insect larvae, etc., which are swallowed whole.. An example from this group is Erpobdella punctata, one of the most common  of  American leeches.  The body is 20-80 mm long,4-7 mm wide and colored a uniform  dark brown or chocolate color with two or four longitudinal rows of blackspots on the dorsal surface.  It is found attached to the
underside of submerged stones or occasionally in organic sediment at the bottom of ponds and from the inside of the outer dead leaves of pond rushes.
 
 Growth in leeches is of two basic types, namely, continuous and step-wise or saltatory.  In  species with continuous growth
,increase in body weight following a meal is less than half the prefeeding weight.  Digestion is rapid and  feeding is frequent ,on
the order of days.  It is characteristic of  predaceous species such as E. punctata and species with rudimentary bloodsucking habits. By contrast, species  with saltatory growth , increase in body weight four, five or more times their prefeeding weight and their weight remains constant between meals. Digestion is slow and feeding infrequent, on the order of weeks or months. Saltatory growth is specialized and characterizes the  higher "bloodsucking" species such as Hirudo medicinalis.
 
 It was long thought that bacteria in the gut carried on digestion for the leech instead of endogenous enzymes which are very low or
absent in the intestine. Relatively recently it  has been discovered  that, ALL  leeches and leech species studied do produce
endogenous intestinal exopeptidases which  can unlink  free terminal-end amino acids, one, amino acid monomer, at a time from a
gradually unwinding and degrading  protein polymer. However, unzipping of the protein can start from either the amino (tail) or carboxyl (head)  terminal-end of the protein molecule. It just so happens that the leech exopeptidase (arylamidases), possibly aided by proteases from endosymbiotic bacteria in the intestine, starts from the tail  or amino protein, free-end , slowly but progressively  removing many hundreds of individual  terminal amino acids for r! esynthesis into proteins that constitute the
leech. Since leeches lack endopeptidases ( proteolytic enzymes that cleave a protein molecule, from within, into smaller  segments
or fragments called  peptides)  the mechanism of protein digestion can not follow the same sequence as it would in  all other animals where exopeptidases act  sequentially on peptides produced by the action of endopeptidases . Exopeptidases are especially prominent in our locally common leech-worm E. punctata. This evolutionary  choice of exopeptic digestion in the Hirudinea distinguishes these carnivorous clitellates  from Oligochaeta.
 
 Deficiency of  digestive enzymes (except exopeptidases) but more importantly deficiency of vitamins, B complex for example, in leeches is compensated for by enzymes and vitamins  produced by endosymbiotic microflora. In Hrudo medicinalis these supplementary factors are produced by an obligatory symbiotic relationship with a single bacterium species, Aeromonas hydrophila, which maintains itself in  pure culture by secreting an antibiotic known to medicine since the 19th century, well before  Fleming's 1929 discovery of penicillin.  Non-bloodsucking  leeches such as E.punctata are host to three bacterial symbionts, Pseudomonas sp, Aeromonas sp, and Klebsiella sp (a slime producer). The bacteria are passed from parent to offspring in the cocoon as it is formed.
 
The  antibiotic is  reported to kill or weaken various pathogens while in the leech gut: Anthrax, Tetanus, Meningitis, and Streptococcal infections. The most important predators on leeches are fish, aquatic insects, crayfish, and other leeches specialized for predation on leeches. Leeches are a favorite food of North America's largest freshwater fish...sturgeon.  A 200 lb. female was recently caught, landed and released , on either a worm or a leech in a  river tributary of Georgian Bay, Ontario, Canada....

 

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