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Goats’ Table Manners: Avoidance of Herbivorous Insects

Tali Berman, Matan Ben-Ari, Tzach Glasser, Moshe Gish and Moshe Inbar

Herbivorous animals (plant eaters) cause physiological, chemical, structural and phenological changes to the eaten plants. This set of changes causes indirect effects (moderated by the plant) to the dispersal and fitness of the herbivorous insects that exploit these plants. However, mammals may have direct effects (via predation and trampling) on the insects while eating the plant matter. These direct interactions have been scarcely studied, and in fact, it is not clear whether and how herbivorous mammals deal with the presence of insects on their food.

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In this study we examined the direct interactions between mammals and herbivorous insects using a model system comprising larvae of Ocnogyna loewii and goats. Due to their polyphagous nature (feeding on a wide range of plants) and their abundance, this system is very convenient for examining the underlying mechanisms of these interactions.

First, we examined how the larvae of O. loewii affect the eating behaviour of the goats by filming and analysing their behaviour while eating. Moreover, we examined how goats locate the larvae on their food by preventing them from using different senses. We found that goats are not deterred by the presence of larvae on the plant due to their efficient ability to sort them (see video #1).

Not one of the many larvae that participated in the study was eaten by the goats. By repeated touching of their food with their mouths (sense of touch),

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the goats detected the presence of larvae on the plant. Leaves with larvae were shaken or thrown away. If a larva entered a goat’s mouth (low probability), the goat felt it (senses of touch and taste) and spat it out, usually without harm (see video #2). As a result, 98% of the larvae survived the goats’ eating. Similar behaviours were observed in response to the presence of silk worms, which are not hairy and dangerous like O. loewii (see video #3).

The sense of sight is not involved in the process at all. Using their sharp senses (that are also effective at night when the insect is hidden) and effective behaviour, the goats manage to eat the plants only, without the insects. This ability of herbivorous mammals to effectively deal with insects on their food highlights the importance and abundance of direct interactions in terrestrial ecosystems.

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