A grasp of the past

by Ricardo Perez-De-La Fuente, research fellow

Few creatures look weirder – or are cooler, in my opinion – than mantidflies. There are around 400 species of these small predatory insects known worldwide – a scarce diversity by insect standards.

Like praying mantises, mantidflies have long ‘necks’ and forelegs armed with powerful spines and other structures used to hunt their prey with a sudden lethal grasp. The unfortunate victims become immobilised until they are meticulously eaten alive – not the best way to spend your last minutes on Earth!

Mantidflies belong to the Neuroptera order of insects and so aren’t actually related to praying mantises, but to insects such as lacewings and antlions.

A new paper that a colleague and I have published presents a new fossil mantidfly from Spanish amber that is important in understanding the evolution of their gripping – or raptorial – forelegs. The finding is presented in the open access journal Scientific Reports today.

Although the discovery has just been published, we excavated the new fossil during the scorching summer of 2010 in Teruel, northeastern Spain.

Amber excavations are very romantic – while they take place we carefully store the amber, piece by piece, into muddy plastic bags, remaining oblivious of what creatures are being unearthed because the amber surfaces have become opaque during fossilisation. Later, in the laboratory, the surfaces of the amber pieces are polished and screened for inclusions. Then a first glimpse is gained into what has remained frozen in time for millions of years.

It is only when the amber inclusions are carefully examined and studied that the implications of the specimens that were dug up years earlier start to be revealed. In this case, a specimen that was preserved in fragments, nothing spectacular at first look, ended up being truly exceptional.

Foreleg of Aragomantispa lacerata, showing powerful spines and other structures adapted to strike and hold prey.

Extinct true mantidflies, particularly those preserved in amber, are extremely rare. Our new fossil, pictured above at the top of the article, is 105 million years old, from the Cretaceous period. It currently stands as the oldest true mantidfly known in amber. The new extinct species, named Aragomantispa lacerata, has allowed us to compare the structures of the raptorial forelegs between extinct and extant mantidflies with an unprecedented detail.

Comparison between the foreleg spine-like structures of the new fossil mantidfly (up), with those from a close modern species (bottom).

Present-day mantidflies have forelegs with spines that bear minute cones at their tip. These cones are sensory organs that elicit the striking reflex and feel the prey’s movements once captured and restrained by the mantidfly’s tight embrace.

The forelegs of Aragomantispa lack these cones at the spines’ tip, instead having larger, icicle-shaped tips. We do not know how sensitive the mantidfly forelegs were in the Cretaceous, but the spines of at least some of these insects seem to be not as specialised as those from their present-day relatives.

Some mantidflies have smaller, reclined hair-like structures forming an edge on the leg’s surface opposing the spines. These reinforced edges create a scissor effect that stuns prey when the forelegs strike. Although Aragomatispa has these structures on the forelegs, they are also different in shape to those found on extant mantidflies.

Reconstruction of Aragomantispa lacerata striking at a hypothetical prey on a fern in the Cretaceous Spanish forest.

The fossil record offers the only direct means to assess when and how the traits characteristic of a given animal group originated in time. However, this kind of fossil evidence appears very occasionally. Our discovery shows that the foreleg spine-like structures of recent mantidflies were not fully developed in at least some of their Cretaceous ancestors.

The most exciting part is to think that this story and literally thousands more lie waiting to be discovered – or otherwise forgotten forever – buried underground.

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