(ORDO NEWS) — Brown bears rub against trees to repel parasites with the smell of tar. Experiments have shown that ticks parasitizing these predators are afraid of the smell of turpentine and beech tar.
Thus, by rubbing against the trunk properly, the bear will protect itself from ticks and get rid of those that have already settled on its body.
In addition, scratching on trees allows you to get rid of shedding hair and leave marks for relatives. Some animals are able to be treated with the help of plants.
For example, common chimpanzees (Pan troglodytes) and bonobos (P. paniscus) remove helminths by swallowing leaves with a rough surface, and male bustards (Otis tarda) during the mating season fight parasitic fungi, protozoa and nematodes by eating poisonous herbs.
Similar behavior has even been described in insects.
For example, caterpillars of Grammia incorrupta butterflies, infected with parasitic larvae of hedgehogs (Tachinidae), get rid of them by eating plants with a high concentration of alkaloids.
A team of zoologists led by Agnieszka Sergiel from the Institute for Nature Conservation of the Polish Academy of Sciences has discovered another example of how animals fight parasites with the help of plants.
Researchers were interested in the habit of brown bears (Ursus arctos) to rub their backs against tree trunks.
According to the traditional explanation, this is how these predators comb out molting wool and leave scent marks for communication with relatives.
However, Sergyel and her co-authors suggested that there is an additional reason for the bears to rub against trees.
The fact is that when the bark is damaged, many trees emit resin, the pungent smell of which is unpleasant for ectoparasites.
Perhaps bears rub against tree trunks to soak up the smell of resin and protect themselves from ticks and blood-sucking insects.
In favor of this idea is the fact that bears prefer to rub against the trunks of coniferous trees, which emit a more odorous resin than deciduous ones.
In addition, sometimes these predators scratch on other strong-smelling objects, such as creosote-soaked power poles.
And bears are more likely to rub against trees during the period of the year when ticks are especially active. However, it remained unclear whether the parasites that live on bears are really afraid of the smell of tar.
To get to the bottom of this issue, Sergiel and her co-authors captured 113 adult meadow ticks (Dermacentor reticulatus) (a species that often parasitizes bears) and performed a series of experiments on them in the laboratory.
During the tests, hungry mites were planted in the middle part of a test tube, at the ends of which there were pieces of filter paper soaked in distilled water, turpentine, or beech tar.
After that, the researchers observed for three minutes which way the experimental individuals would go. It turned out that ticks really don’t like the smell of turpentine.
They never entered the paper impregnated with this substance and tried not to approach it closer than a few centimeters. By comparison, mites frequently visited the end of the tube with water-soaked paper.
The paper impregnated with beech tar did not like the mites either. Although they occasionally came into contact with it, this was less common than with water-soaked paper.
At the same time, the individuals who tried the side of the test tube with turpentine or tar, visited it only one.
Additional analysis showed that the mites, smelling turpentine or tar, mainly tried to move closer to the end of the test tube with paper soaked in water.
At the same time, their relatives, who were in the test tube, where the water-soaked paper lay at both ends, remained in its middle part.
The results of the study confirm that meadow mites that parasitize brown bears do not tolerate the smell of tree resin, especially coniferous trees. Most likely, these conclusions are true for other types of ticks.
Thus, if a bear rubs against a tree trunk and becomes saturated with the smell of resin, it will provide itself with effective protection against ticks and be able to get rid of those that have already settled on it.
At the same time, in order for the effect of the repellent to continue, the predator will need to regularly repeat the procedure.
Interestingly, this is not the first example of brown bears self-medicating with plants.
Previously, zoologists have found that in North America, these predators use oshu (Ligusticum porteri), a plant from the umbrella family, to fight blood-sucking insects.
To do this, the bears chew it, and then grease the wool with the resulting paste.
Giant pandas (Ailuropoda melanoleuca) have learned to cover themselves with fresh horse manure to keep them cool in cold weather.
The caryophyllene and caryophyllene oxide contained in the litter inhibit the work of thermosensitive receptors responsible for the perception of cold.
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