To cover the body with detritus to camouflage
The fossil, about four millimetres long, is a predatory larva of the order Neuroptera. It is covered by a tangle of filamentous plant remains that it collected with its jaws to form a defensive shield and camouflage itself. This kind of behaviour, the trash-carrying, is a survival strategy observed in current species to render them nearly undetectable to predators and preys. The fossil, related to current green lacewings, represents a new genus and species designated Hallucinochrysa diogenesi, alluding to its mind-blowing appearance and resemblance to Diogenes syndrome, a human behavioural disorder characterized by compulsive hoarding of trash.
According to the study, the filamentous plant remains composing the larval trash packet are recognised as trichomes, that is, plant hairs with diverse shapes and functions. Observing the morphology, micro-structure and composition of these trichomes, researchers were able to state that they belonged to ferns.
Today green lacewing larvae harvest plant materials or even detritus and arthropod remains and carry them on their backs, nestled among small tubercles with hairs. On the contrary, Hallucinochrysa diogenesi possessed a bizarre, unique morphology; it showed extremely elongated tubercles, with hairs that had trumpet-shaped endings acting as anchoring points. All this structure, completely unknown until now, formed a dorsal basket that retained the trash and prevented it from sliding when the insect moved.
The most ancient insect camouflage
In the authorsʼ opinion “Hallucinochrysa diogenesi proved that camouflage strategy and its necessary morphological adaptations early appeared in insects; they already existed in the era of the dinosaurs. In the case of green lacewings, it can be stated that this complex behaviour has not changed for at least 110 million years. This fact constitutes a relevant piece of information for evolution studies about animal behaviour and the adaptation strategies of organisms throughout Earthʼs history”.
The study also shows, providing then an outstanding data, a close ancient plant-insect interaction —possibly an example of mutualism—; the predatory larvae saved ferns from plagues, whereas ferns provides larvae with a habitat and protecting remains; in other words, both organisms profited from each other. In a Cretaceous scenery where resin forests in the ancient Iberian Peninsula were razed by wildfires, this larva collected remains from a fern that grew abundantly after wildfires.
El Soplao outcrop, where the discovery was made, is one of the most important current references to unravel evolution mysteries of Earth invertebrates and better know how the forest ecosystems were 110 million years ago. The study, which is part of the researches developed by AMBARES group (Ámbares de España), has been possible thanks to the collaboration of El Soplao cave, SIEC, and the Government of Cantabria; the study was funded with regional, Spanish and North American funds.