Posted: Jul 12, 2017 2:17 pm
Actually, cannibalism in Lepidoptera larvae is a well-documented phenomenon. Here in the UK, the larvae of the Orange Tip, Anthocharis cardamines, are cannibalistic in the first instar in the wild. Larvae of two Nocutid moths, the Dun-Bar (Cosmia trapezina) and the Satellite (Eupsilia transversa), are carnivorous toward other Lepidoptera larvae in the wild, and will exhibit cannibalism in captivity, to the point where captive rearing of the larvae of these species requires segregating the larvae in individual containers. These species will attack other Lepidoptera larvae in the wild, as a means of eliminating food competition, and will also weed out other individuals of their own species in an overcrowding situation on a given foodplant.
Spodoptera exigua, the Small Mottled Willow, is a migrant species from the UK standpoint, and resident in continental Europe, with no previous documented carnivorous behaviour associated with its larvae. As a consequence, the emergence of carnivorous behaviour under experimental conditions is interesting to put it mildly, and it's worth pursuing whether this switch is a feature restricted to this species, or more widespread. It's also worth noting that this species is a member of the same taxonomic SubFamily as the two moths I cited above as having documented carnivorous behaviour in the wild (all three are members of the Xyleninae). It's possible that carnivory is a latent trait within Xylenines, expressed under certain conditions, and that the two documented carnivorous larvae cited above express this trait because the conditions are met in these species.
Spodoptera exigua, the Small Mottled Willow, is a migrant species from the UK standpoint, and resident in continental Europe, with no previous documented carnivorous behaviour associated with its larvae. As a consequence, the emergence of carnivorous behaviour under experimental conditions is interesting to put it mildly, and it's worth pursuing whether this switch is a feature restricted to this species, or more widespread. It's also worth noting that this species is a member of the same taxonomic SubFamily as the two moths I cited above as having documented carnivorous behaviour in the wild (all three are members of the Xyleninae). It's possible that carnivory is a latent trait within Xylenines, expressed under certain conditions, and that the two documented carnivorous larvae cited above express this trait because the conditions are met in these species.