Lepidopteran Caterpillars in Ambers from Lebanon, Myanmar, Mexico, and the Dominican Republic Indicate Diversification of Defensive Structures and Increasing Abundance over Time

Caterpillars are still rare as fossils, but most commonly preserved in ambers. We report here twelve additional specimens from four different types of ambers plus one caterpillar in Tanzanian Holocene copal. Most of these prove to be challenging to be dealt with from a taxonomic point of view. Despite this challenge we measured protruding defensive structures, setae and spines, and compared these between the types of amber and according to age. We furthermore compared the relative abundance of caterpillars in ambers in relation to larvae of another extensively sampled group in amber, namely Neuroptera. Our results show that the maximum length of protruding structures becomes successively longer over time, reaching the highest extreme in the modern fauna. Yet, already in the Miocene very long setae have occurred, as demonstrated by a new fossil from Dominican amber. Relative abundances of caterpillars in relation to lacewing larvae in resins increase significantly and steadily over time. Combining both aspects indicates an increase in diversity of morphological structures of caterpillars and an increase in abundance. At the same time lacewing larvae lost diversity and abundance towards the modern fauna. The results demonstrate that taxonomically challenging fossils carry ecologically meaningful information and should not be ignored.