Topical use of a potentially medicinal plant acting as a repellent against insects has been already observed in brown bears. But do brown bears rub against resinous trees also for anti-parasitic self-medication, in addition to the more widely accepted chemical communication function? Our newly published paper aimed at bringing some elements together to answer this question. To Dermacentor reticulatus ticks we offered a binary microhabitat choice in individual horizontal tubes with resin products that are known to attract bears and elicit rubbing behaviour (turpentine or beech tar) placed on filter paper at one end, and control substance (neutral distilled water) at the other.
Beech tar and turpentine, elecit brown bears rubbing behaviour and share several chemical properties with natural resin that flows when bears are clawing trees before rubbing against them. Brown bears rub different body regions depending on the season, age and sex, but the core postures include areas preferred by ticks to attach. Moreover, the peak of tree-rubbing behaviour in bears also co-occur with the peak of tick’s host-seeking behaviour and of infestation levels. In this study, we found that ticks almost consistently touched neutral ends while avoided treated ones, and did not spend more than one minute at a treated side. These findings suggest that rubbing against substances with intense smells may also carry an anti-parasite behaviour trait, having the function of limiting tick infestation levels in addition to the more widely accepted chemical communication function.
More in the article „Anti-parasitic function of tree-rubbing behaviour in brown bears suggested by an in vitro test on a generalist ectoparasite” by A. Blaise, D. Kiewra, K. Chrząścik, N. Selva, M. Popiołek, A. Sergiel