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Effect of ale, garlic, and soured cream on the appetite of leeches

By Anders Baerheim and Hogne Sandvik who were awarded the prestigeous Ig Nobel Prize in biology for their scientific achievements. You may listen to a RealAudio recording of the Ig Nobel Prize Ceremony

The Journal of the Norwegian Medical Association recently published an experimental study on the protective effect of garlic against vampires. Rather surprisingly, this study showed that garlic seems to have an attractive force on leeches (and probably also on vampires).

Leeches are used in microsurgery to prevent harmful swellings in replanted body parts. Sometimes however, the leeches refuse to do their job properly. To stimulate the leeches' appetite several remedies have been used, such as immersing them in strong beer before application or smearing soured cream on the skin. The present study was designed to evaluate the effect of these remedies (ale, garlic, and soured cream). It was published in the BMJ (British Medical Journal) 1994; 309: 1689.


Differences in willingness to bite were measured by median time from application on Hogne's forearm to biting him. Some leeches did not bite within the predefined time limit of 300s, but as the study was run according to the intention-to-bite principle, these incidences were registered with a time interval of 301s in the statistical analysis.

Six leeches were dipped briefly in one of two different types of beer (Guinness Stout or Hansa Bock) or in plain water (control) before being placed on the forearms. Each leech was, in random order, exposed three times to each liquid. As serotonin probably is involved in controlling feeding behaviour, we also measured the serotonin content of both beers (high-pressure liquid chromatography).

After having been exposed to beer, some of the leeches changed behaviour, swaying their forebodies, losing grip or falling on their backs. Leeches dipped in Guinness bit after 187s, those dipped in Hansa after 136s, and controls after 92s. The serotonin content was low, and similar for the two beers (0.1 ug/ml).


After having completed the first part of the study the leeches became lazy, their scientific enthusiasm diminished. Discipline failed, appointments were forgotten, some even ran away on their own.

In the next study part six other leeches were therefore used. This time the left forearm was either smeared with soured cream or not prepared at all. Leeches exposed to soured cream were often seen sucking frantically on the wall of their container after they had been on the arm. While on the cream-smeared arm however they bit no sooner than the controls.


The other forearm was smeared with garlic. Two leeches placed on this arm started to wriggle and crawl without assuming the sucking position. They were placed in water, but their condition deteriorated. When placed on a bare arm they tried to initiate feeding, but did not manage to co-ordinate the process. Both died 2-3 hours after the exposure to garlic. For ethical reasons the garlic arm was abandoned at this point.

We believe this to be the first study showing lethal effect of garlic by skin absorption. Garlic has a definite force of attraction on leeches, but further research into this fatal attraction can only be performed by in-depth qualitative methods.


Let this study be a reminder of how medical beliefs may stand uncontradicted for decades. We should never forget the necessity of critical research on commonly accepted medical truths.


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Department of Public Health and Primary Health Care, last updated 15.09.02

Hogne.Sandvik@isf.uib.no