Researchers studying amber containing the larvae of Cretaceous insects reveal that immature lacewings likely specialized in killing spiders. They walked across spider webs with ease thanks to long, thin legs and serrated claws, according to findings published in Current Biology last month.
Today, lacewings and their relatives are mostly predatory. In their immature stages, they have modified jaws that allow them to pierce their prey and drain its fluids. The larvae of green lacewings, in particular, have unique specializations (both anatomically and behaviorally) for approaching and subduing prey, including camouflage. Early relatives of modern green lacewings were called mesochrysopids.
A team led by China Agricultural University’s Xingyue Liu and Michael Engel from the University of Kansas, Lawrence, examined 100-million-year-old amber from the Hukawng Valley of Kachin in northern Myanmar. These contained both adult and juvenile mesochrysopids, including a new ancient lacewing species they named Pedanoptera arachnophila. The adults have a forewing length of 7.7 millimeters, elongated legs, and a prolonged body. The larvae were equipped with long, thin, curved toothless “jaws” and extremely long, slender legs that ended with serrated claws. Compared to these appendages, its body was relatively massive.
The adults enjoyed a predatory lifestyle, though, unlike their larvae, the adults were likely generalists. The larvae, however, had features usually found in spider-associated insect groups. The claws on the larvae allowed them to grasp the silken threads of web-spinning spiders without becoming entangled. The researchers can’t say for sure why the larvae were entering spider webs, but they think the immature lacewing were preying on the spiders themselves – rather than acting like kleptoparasites and stealing prey captured by spiders. “Their massive bodies would have made hiding within a web virtually impossible,” the team wrote.
Spiders were both diverse and abundant in Burmese amber forests. And while web-spinning spiders were very skilled at catching bugs that fly, several insect lineages evolved strategies for hunting spiders themselves. It’s unclear how far back these spider-insect associations developed. Pedanoptera arachnophila demonstrates that by the mid-Cretaceous, at least one insect lineage had already evolved extreme traits that allow them to enter spider webs.
