Insects exhibit a wide diversity of anatomical specializations in their adult and immature stages associated with particular aspects of their biology. The order Neuroptera (lacewings, antlions, and their relatives) are a moderately diverse lineage of principally predatory animals, at least in their immature stages, as all have a modified piercing-sucking mandible-maxillary complex that allows them to drain fluids from their prey. As such, the larvae of various groups have evolved unique anatomical and behavioral specializations for approaching and subduing their prey, particularly the green lacewings (Chrysopidae), where immatures are also adept at camouflage [1-4]. Here we report the discovery of a unique mode of life among mid-Cretaceous mesochrysopids, an early stem group to modern green lacewings [5-7] exhibiting a combination of morphological modifications in both adults and larvae unknown among living and fossil Neuroptera, even across winged insects. The new mesochrysopids exhibit a uniquely prolonged thorax, elongate legs, and dramatically reduced hind wings in adults, and larvae have extremely elongate, slender legs with pectinate pretarsal claws and lacking trumpet-shaped empodia. The peculiarities of the larvae include features principally found in spider-associated insect groups, implying that these lacewings were early specialists on web-spinning spiders, either as active predators or kleptoparasites. This reveals a dramatic and ancient degree of ecological refinement in a major lineage of insect predators, for a food resource otherwise not utilized by most lacewings.
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