There are many reasons explaining why bears rub their backs against tree trunks.
Sometimes, they do this to mark their scent on the tree, and other times it’s to scratch themselves in hard-to-reach places. A recent study has revealed another reason: using natural tick repellents. When a bear rubs against a tree trunk, the tree secretes sap. Oak sap adheres to their fur and skin for a long time and has waterproofing properties, making it a potential “candidate” for the most effective tick repellent.
Bears rub their backs against tree trunks to repel ticks on their bodies.
According to scientists, animals rarely exhibit complex behaviors, such as rubbing against a tree for just one reason. Over many years, they observed that grizzly bears and black bears prefer certain types of trees, especially oaks, to the extent that scientists have used the strong scent of oak sap to “lure” bears for research or into zoos.
To test the hypothesis that tree sap could treat ticks, scientists placed Dermacentor reticulatus, a type of hard tick that primarily lives on bears, in the middle of a horizontal tube. One end of the tube contained oak sap, while the other end contained distilled water, and they observed which way the ticks would go. The result showed that they ran towards the end of the tube with distilled water, with some ticks moving very quickly and hiding under the water. The scientists also experimented with pine sap, and the results were similar: the ticks ran towards the end of the tube with distilled water.
The researchers focused on ticks because they have a wide geographical distribution and are quite adaptable to different environments. Due to climate change, they are spreading further and becoming more active. Ticks are also disease carriers, although scientists are still unsure what diseases they transmit to bears.
The results of this study provide the first experimental evidence supporting the idea that tree sap could be a natural insect repellent. Other animals in nature also have ways to repel insects using natural resources; for example, capuchin monkeys often rub their fur with citrus peels, dolphins can clean their skin with coral, and cats may use mint leaves to repel mosquitoes. Thus, it is understandable that bears rub against tree trunks for similar reasons.
