In the realm of entomology, few creatures command as much fascination as the mantis. Throughout history, these striking insects have been deeply woven into local myths and legends, sometimes respected as mystical soothsayers that can guide lost travelers home, and other times feared as little devils.

Today they remain captivating animals, serving as excellent bioindicators of biodiversity, and helping us identify rich and diverse ecosystems when present as native species.

However, a new study published in the open-access Journal of Orthoptera Research reports that two mantis species identified in Europe - Hierodula tenuidentata and Hierodula patellifera - have been formally recognised as Invasive Alien Species (IAS). This shift in status highlights a growing threat to the biodiversity that native mantises typically help us protect. Led by Roberto Battiston of the Museum of Archaeology and Natural Sciences “G. Zannato”, a team of researchers investigated the impacts of these native to Asia species on European ecosystems which, until now, were largely unknown.

According to Battiston, these mantises have been present in Europe for about a decade, but their numbers have recently exploded in the Mediterranean and continental regions.

“They are pushing increasingly further north, thanks to climate change,” Battiston explains, noting that viable populations are now frequently spotted by the public in local parks and gardens. Because they are large and fascinating, they often inspire more curiosity than concern, with members of the public frequently wondering if these striking insects are a positive sign for their local environment. “This study was born to give people those answers and to develop strategies to contain them”, Battiston adds.

Hierodula tenuidentata and Hierodula patellifera are large and adaptable tree-dwelling predators, characterised by their high reproductive potential. They are capable of hatching an average of around 200 nymphs per egg case, which is almost double that of the native European mantis (Mantis religiosa). Coupled with their low rate of cannibalism among young nymphs, they are able to grow very rapidly.

These species are considered particularly dangerous to local biodiversity because they fatally lure native males into mating attempts that end in the males being eaten, potentially depressing native populations. They additionally consume a wide range of other native species, including essential pollinators like honeybees, and small protected vertebrates such as lizards and tree frogs. These negative interactions demonstrate the need for urgent assessments, particularly in Mediterranean islands with endemic species of invertebrates and vertebrates.

Interestingly, domestic cats have emerged as the primary vertebrate predator of the invasive Asian mantises, accounting for 45% of recorded positive predation events. Battiston notes that while cats serve as an effective means of containment for these invaders, they are unable to distinguish between alien and native species. Consequently, roaming cats also prey on native species like the European mantis, which already suffer competition from their exotic cousins in peri-urban environments and are in decline.

Human-modified environments, particularly in urban and suburban areas, significantly facilitate the expansion of Hierodula mantises. These insects utilise artificial structures, such as insect hotels, as concentrated hunting grounds, and leverage urban heat islands to survive longer into colder months. Thus, by exploiting human infrastructure and localised warming, these mantises are successfully extending their range and survival beyond natural limits.

To mitigate the spread of Hierodula, Battiston mentions the following initiative:

“My colleagues William di Pietro and Antonio Fasano (GRIO) have managed to set up a huge citizen science project and collect over 2,300 reports from enthusiasts and citizens. Citizen science is a fundamental tool not only for monitoring but also for raising awareness and informing people in an active and participatory way about these issues.”

Beyond reporting sightings, the public can also take direct action by intervening during the winter months when trees and shrubs are leafless. During this time, the oothecae - brownish, spongy egg cases about 2-3 cm in size - are well-exposed and easily recognisable on branches. While these cases are easy to remove and their destruction is painless, Battiston cautions that the public should always consult a specialist before removal to ensure that they are not accidentally targeting native mantises.

The expansion of the Asian mantis is a powerful reminder of how human activity shifts natural boundaries and makes active community-led conservation more important than ever. As these adaptable invaders continue to reshape European ecosystems, our collective vigilance and participation in citizen science are effective tools for protecting Europe's native biodiversity.