Shrew Culture, Myths, Stories and Poisonous Facts...

Poisonous Shrews

"...it biteth deep and poysoneth deadly..." (E. Topsell, 17th century)

There is evidence that a few shrew species produce a toxic secretion, which probably helps to immobilise especially large prey, such as other small mammals, reptiles, amphibians, fish and larger invertebrates, by its effects on the nervous system. This poisonous bite has been reported from North American Blarina and European Neomys. The bite can be quite painful to a human hand for, although shrew's teeth rarely puncture the skin, the toxin in the saliva of some species seems to produce a slight inflammation and reddening of the skin which can persist for several days.

The learned author of the "Speculum Mundi" thus portrayed the shrewmouse: "...In Latine it is called Mus araneus, because it containeth in it poison or venime, like a spider, and if at any time it bite either man or beast the truth of this will be apparent..."

Already the ancient Greeks and Romans believed that shrews were evil. Throughout history they have been thought of as poisonous and even deadly. English rustics still say so. If a shrewmouse ran over the limb of man or beast, paralysis of such limb followed. Horses or cattle stiff in the joints or otherwise lame, were asserted to be "shrew-struck". In "Historia Animalium" by Aristoteles there is a passage about the effect of the shrew bite to horses: "Shrew's bites are dangerous, as also to other beasts of burden: blisters develop. The bite is more dangerous if the shrew is pregnant when it bites; for then the blisters burst, while otherwise they do not. (Translated by D.M.Balme).

There are many records of these dangerous beasts dating from the 17th century to the present, but the scientific results are sometimes controversal and lack toxicologic analysis. It would be interesting to know more about the neurotoxic agent in the saliva of shrews and what the exact concentrations are. Three mammal groups are said to have some kind of toxic agent: platypus from Australia, solenodons from Cuba, and of course shrews. In some literature moles are said to also have venomous saliva.

After so many years this topic was warmed up by a simple question Brent (Iowa State University) posted to the Mammal-L newsgroup:

I've always thought that Blarina brevicauda has a neurotoxic venom in it's saliva. Where I got this particular idea, I have no idea, but assuming that it is true, does anyone know what the behavioral effects of this might be on a stricken adult Microtus pennsylvanicus? And, is this venom sufficiently potent that a good bite into the vole's musculature will transfer sufficient venom to kill the animal without further attacking the animal? I ask in as much as I found a M. penn. that would only run in counter-clockwise circles this morning. It was a mature adult. I easily caught it, and found that it was bleeding from very minor tail and foot wounds, but otherwise unharmed as far as I could tell. I could think of no reason for it's odd behavior, which frantically continued as soon as I released it, other than some sort of toxic effect. And, Blarina are the only candidates for toxic critters in this area. Last I saw, it was spiralling across the prairie making easy hawk bait of itself, but no Blarina was to be found lurking nearby. - Brent

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Accounts & Descriptions of the effects of shrew bites:

According to hitherto accounts on the effect of a shrew bite, the topic is quite controversal, and it might be useful to also hear reports of Blarina 'victims' that showed no reaction to the bite. Blarina's poison might cause an allergic reaction such as an anaphylactic shock, to which not everybody is susceptible.

These data were compiled for a review of shrew poison. I would be thankful to receive any further reports on this topic.

Maynard, C. J. 1889. Singular effects produced by the bite of a short-tailed shrew, Blarina brevicauda. Contributions to Science, 1:57-59.

"All this occupied perhaps thirty seconds, when I began to experience a burning sensation in the first two bites, followed by a peculiar sensation ... in the right hand. I walked to the house, only a few hundred yards away, but by this time, the pain which had been rapidly increasing, had become quite severe, and by the time I had placed the shrew in an improvised cage, I was suffering acutely. The burning sensation, first observed, predominated in the immediate vicinity of the wounds, but was now greatly intensified, accompanied by shooting pains, radiating in all directions from the punctures but more especially running along the arm, and in half an hour, they had reached as high as the elbow. All this time, the parts in the immediate vicinity of the wounds, were swelling, and around the punctures the flesh had become whitish. I bathed the wounds in alcohol and in a kind of liniment, but with little effect. The pain and the swelling reached its maximum development in about an hour, but I could not use my left hand without suffereing great pain for three days, nor did the swelling abate much before that time. At its greates development, the swelling on the left hand caused that member to be nearly twice its ordinary thickness at the wound, but appeared to be confined to the immediate vicinity of the bites, and was not prominent on the right hand; in fact, the first wound was by far the most severe. The burning sensation disappeared that night, but the shooting pains were felt, with less and less severity, upon exertion of the hand, from the elbow downward, for a week, and did not entirely disappear until the total abatement of the swelling, which occured in about a fortnight."

(Excerpt provided by Luis A. Ruedas)

I am not at all sure that the toxin is used to subdue anything and suggest that it is not. The literature suggests they eat mice, and they do at times (see old paper by Bob Eadie in J.M.), but apparently only when mouse populations are huge, and then probably only young ones. Blarina feeds mostly on earthworms, snails, centipedes, beetles, etc. They are not about to start feeding on larger animals. I have been bitten by a Blarina. I put my finger down at the far end of a 10 gallon aquarium. The shrew immediately came running over and bit me. It got me pretty good. I had no reaction whatever. Either I am not alergic to Blarina bite, orperhaps the toxin in the saliva is only emitted under certain conditions.

John Whitaker

One of my colleagues was once bitten by Blarina - the shrew managed to really chomp her - the arm became very swollen, and she was also in a lot of pain. Cannot remember the timeframe for all the post-bite events, but somehow do recall many of the symptoms lasting for at least a day.

Lita Pinter

I have been bitten by Blarina. The bite was painful, but more odd feeling than severe. My skin was broken and I did bleed a bit. I had a mild 'tingly' feeling, but no other major symptoms. I do recall that my finger was a bit numb for a few hours afterwards. We have observed our short-tails attacking live voles, etc., and consuming dead M. ochrogaster, S. hispidus, P. maniculatus., etc.

Billy Schweiger

Over the last year and a half I have kept several Blarina in captivity, and have watched them rather intently, particularly when they feed. The first individuals I had were fed solely crickets and earthworms. The shrews would immediately run around quite quickly in the 10 gallon aquarium and "bite" each of the crickets, then cache them together often in a corner or a piece of tubing in the aquarium. On more than one occassion I returned several hours later to discover that the insects, although unable to move, were still alive. The only movement that could be detected, which was slight and slow, was in antennae and some legs. The insects were very much alive and the shrews would simply go and partake at their leisure. When a Blarina was fed a large earthworm, they would frequently bite all along the length of the body, which appeared to immediately numb those regions, followed quickly by total paralysis and assumed death. If it was a particulary large earthworm however, the part that remained was usually also cached for further consumption later.

Robert L. Connour II

In the June 20 newletter, a question was posed concerning Blarina bites and the effect in humans. In an early paper, a reaction to a Blarina bite was described in which it swelled up and hurt for days. However, I have been bit and had no such reaction. It is rare that the skin is broken to where the venon can be "applied". Even when this occurs, the reaction may depend on the person (this may or may not be similar to anaphylactic shock).

For original papers, see:

O. Pearson, 1942, J. Mammalogy 23: 159-166

O. Pearson, 1956, in VENOMS edited by E. Buckley AAAS 44 S.

Ellis & O. Krayer, 1955, J. Pharm Exper Therapeutics 114: 127-137

T. Tomasi, 1978, J. Mammalogy 59: 852-854

Tom Tomasi

question about how poisonous shrews prevent the neurotoxin from being self-reactive...

(... )lack of data on the chemical makeup of the venom and its target cells in the prey. However one could speculate that to be active the venom must enter the blood stream or the extracellular fluid in the immediate vicinity of the target cells. In the shrews, the venom in the saliva would normally be swallowed and enter the stomach where the acidic environment and digestive enzymes would break it down and deactivate it. Why wouldn't venom be absorbed through oral tissues and enter the blood stream? The venom molecule may be too large to move readily into the blood stream from the oral cavity (evidence suggests that the venom is a protein), or the shrew may have a protein in its blood that binds to the venom and inactivates it when it enters the shrews blood stream. Another possibility is that the venom is not present in the saliva at all times, but is only released into that fluid when the shrew attacks a prey. Any or all of these are possibilities, but only time and further research will clarify the situation.

Keith A. Carson In view of the, sometimes controversal reports on the severity of shrew bites, it might be appropriate to take into account the possibility of "passive toxicity", at least in some cases, as W. Bujatti suggested:

Some animals are not actively poisonous, but their victims still suffer from toxic effects, e.g. 1) Moray eels (Muraenidae, Pisces) do not produce venom, but it is assumed that "ptomaine poisons" account for their victims being 'poisoned'. 2) Komodo dragons (Varanidae, Reptilia), also scavengers, were shown to bite their prey only once and then wait until their victims become weak, which can take upto two weeks.

If this were the case with the shrew Blarina, the 'ptomaine poison' should be detectable in the shrew's saliva.

Acknowledgements:

For providing literature and sharing personal accounts and thoughts I would like to thank Wolfgang Bujatti (Univ. of Vienna, Federal Ministry of Environment of Austria), Keith A. Carson (Dept. of Biology, Old Dominion University, Norfolk), Robert L. Connour II (Dept. of Biology, Western Illinois Univ.), Lita Pinta, Luis A. Ruedas (Museum of Sothwestern Biology, Univ. of New Mexico), Jukka Savolainen (Dept. of Biology, Univ. of Joensuu), E. William Schweiger (Dept. of Systematics and Ecology, Univ. of Kansas), Thomas E. Tomasi (Southwest Missouri State University), and John Whitaker (Indiana State Univ.).

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Further Literature:

591 Bücherl, W., E. Buckley, V. Denlofen (eds.) (1968): Venomous animals and their venoms. Vol. I. Venomous vertebrates. Academic Press, New York.

719 Carson, K.A., R.K. Rose (1985): Ultrastructure of the submandibular gland of the venomous short-tailed shrew, Blarina carolinensis. Anat. Rec. 211 (3): 35a-36a.

xxx Carson, K.A., R.K. Rose (1993): Fine structure of the submandibular gland of the venomous short-tailed shrew, Blarina brevicauda Say (Insectivora, Soricidae). Eur. J. Morphol. 31: 111-128.

908 Cranbrook, The Earl Of (1959): The feeding habits of the water shrew, N. fodiens bicolor Shaw, in captivity and the effect of its attack upon its prey. Proc. Zool. Soc. Lond. 133(2): 245-249.

1055 Demeules, D.H. (1954): Possible anti-adrenalin action of shrew venom. J. Mamm. 35 (3): 425.

xxx Dufton, M.J. (1992): Venomous mammals. Pharmacol. Ther. 53: 199-215.

1265 Eadie, W.R. (1944): The short-tailed shrew and field mouse predation. J. Mammalogy 25: 359-364.

1268 Eadie, W.R. (1948): Shrew-mouse predation during low mouse abundance. J. Mammalogy 29: 35-37.

1270 Eadie, W.R. (1949): Predation on Sorex by Blarina. J. Mammalogy 30: 308-309.

1271 Eadie, W.R. (1952): Shrew predation and vole populations on a localized area. J. Mammalogy 33: 185-189.

1310 Ellis, S., O. Krayer (1955): Properties of a toxin from the salivary gland of the shrew, Blarina brevicauda. J. Pharm. Exp. Therapeutics 114 (2): 127-137.

2939 Kraft, R., G. Pleyer (1978): Zur Ernährungsbiologie der europäischen Wasserspitzmaus, Neomys fodiens (Pennant, 1771) an Fischteichen. Z. Säugetierk. 43: 321-330.

3089 Lawrence, B. (1945): Brief comparison of short-tailed shrew and reptile poisons. J. Mammalogy 26 (4): 393-396.

xxx Lopez-Jurado, L.F., J.A. Mateo (1996): Evidence of venom in the Canarian shrew (Crocidura canariensis): immobilizing effects on the Atlantic lizard (Gallotia atlantica). J. Zool. Lond. 239: 394-395.

3340 Martin, I.G. (1981): Venom of the short-tailed shrew (Blarina brevicauda) as an insect immobilizing agent. J. Mammalogy 62(1): 189-192.

3419 Maynard, C.J. (1889): Singular effects produced by the bite of a short-tailed shrew, Blarina brevicauda. Contr. Science 1: 57-59.

3918 O'Reilly, R.A. (1949): Shrew preying on ribbon snake. J. Mammalogy 30: 309.

4096 Pearson, O.P. (1942): On the cause and nature of a poisonous action produced by the bite of a shrew (Blarina brevicauda). J. Mamm. 23 (2): 159-166.

4105 Pearson, O.P. (1956): A toxic substance from the salivary glands of a mammal (short-tailed shrew). In: E.E. Buckley, N. Porges (eds.). Venoms. Publ. no. 44, Amer. Ass. Adv. Sci., Wash. 44: 55-58.

4258 Pournelle, G.H. (1967): Classification, biology and description of the venom apparatus of insectivores of the genera Solenodon, Neomys, and Blarina. In: Pournelle, G.H. (ed.): Venomous animals and their venoms. Pp. 31-42. New York: Academic Press.

4298 Pucek, M. (1957): Die toxische Wirkung der glandulae submaxillares bei Neomys fodiens fodiens Schreb. Bull. Acad. Pol. Sci., Cl. II, Ser. Sci. Biol., 5 (9): 301-306.

4299 Pucek, M. (1959): The effect of the venom of the European water shrew (Neomys fodiens fodiens Pennant) on certain experimental animals. Acta Theriol. 3(6): 93-104.

4300 Pucek, M. (1959): Venomousness in mammals. Przegl. Zool. (A7) 3: 106-115.

4304 Pucek, M. (1967): Chemistry and pharmacology of insectivore venoms. In: Pounelle, G.H. (ed.): Venomous animals and their venoms. Vol. 1: 43-50. New York: Academic Press.

4305 Pucek, M. (1969): Neomys anomalus Cabrera, 1907, a venomous mammal. Bull. Acad. Pol. Sci., Cl. II, Ser. Sci. Biol., 17: 569-573.

5488 Tomasi, T.E. (1978): Function of venom in the short-tailed shrew, Blarina brevicauda. J. Mammalogy 59(4): 852-854.

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