Evolution and function of stick insects' "mushroom sensilla"

Some ground-dwelling stick insects (Phasmatodea) contain sensillae with mushroom-like shape of yet unknown function. These mushroom sensillae are located in two (e.g. Sungaya inexpectata) or three (e.g. Epidaris nolimetangere) fields on the ventral prosternite, each containing up to 60 individual sensillae. Phylogenetic studies revealed that ground-dwelling stick insects derived from tree-dwelling ancestors and that species of both groups contain mushroom-sensilla despite the fact that they are not closely related to each other. However, a high degree of similarities between mushroom-sensilla of different stick-insect species indicates homology between these sensilla, which in turn makes a re-evolution or reduction of sensilla in certain species more likely than their convergent evolution.