When the group denies individual nutritional wisdom

In social insects, decisions are usually predicted to be more accurate than individual decisions, because individual preferences are amplified at the group level. Although social caterpillars, as individuals, possess considerable ‘nutritional wisdom’ and have the capacity to regulate their nutrient intake: does this mean that the collective nutritional decisions made by colonies are better? We investigated individual feeding responses and collective decisions when caterpillar colonies were faced with different food sources. Forest tent caterpillars, Malacosoma disstria, had to choose between nutritionally balanced and unbalanced food sources placed at opposite ends of a bridge. At the individual level, caterpillars showed a clear preference for the balanced food source. In contrast, at the collective level, colonies of caterpillars randomly chose one of the two, and then became trapped for at least 24 h as a result of trail following behaviour. If the first caterpillar found the unbalanced food, it was followed by the others and the colony was unable to reverse this choice. This study provides evidence for a novel potential cost to group living, and shows that group feeding behaviour cannot always be simply predicted from individual preferences.