In findings published in the Journal of Orthoptera Research, researchers have determined that two species of giant praying mantises native to South Asia are negatively impacting European ecosystems and officially classified them as invasive.
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This classification follows extensive research conducted by Roberto Battiston from the G. Zannato Museum of Archaeology and Natural Sciences (in Vicenza, Italy) and his team.
The species – Hierodula tenuidentata and Hierodula patellifera – have been present in Europe for around a decade, but their populations have risen greatly recently, especially throughout Mediterranean and continental regions, posing great risks for native (and often endemic) wildlife.
“They are pushing increasingly further north, thanks to climate change,” said Battiston.
Established populations of the species are regularly reported in parks and gardens, and many people don’t even realise they’re invasive due to their striking appearance.
“This study was born to give people those answers and to develop strategies to contain them,” Battiston explained.
The impact
There are several reasons why these praying mantises have been able to make themselves at home in Europe. First, they reproduce rapidly, with H. tenuidentata hatching an average of 209 young in one egg case, nearly twice as the native European mantis (Mantis religiosa). The researchers have also observed low cannibalism rates among the young, further supporting population growth that could lead to them dominating these habitats within a few reproductive cycles.
Humans are playing their part too – urban and suburban areas pose ideal conditions for praying mantises, with helpful structures like insect hotels becoming perfect hunting sites. Furthermore, as urban areas tend to get warmer, the mantises can stay active until later in the year.
European mantis males are attracted to the pheromones of females of the invasive species, but their attempts to mate never end well: in the majority of encounters, the female ends up eating them.
Apart from the unsuspecting males, these Asian praying mantises also feed on a wide range of native animals, such as honeybees and small vertebrates often protected by EU legislation. For example, the common wall lizard or Perrin’s tree frog.
Teamwork
Hierodula mantises are not without enemies, however. The study found hornets (Vespa crabro) to be their major insect predator. Stink bugs (Halyomorpha halys and Nezara viridula) were observed piercing the mantis’ developing eggs with their mouthparts. Native ant species (Crematogaster scutellaris) were seen nesting inside hatched egg capsules of Hierodula mantises.
Vertebrate predators included the Eurasian golden orioles (Oriolus oriolus) and the little owl (Athene noctua), but the leading one was the domestic cat (Felis catus), accounting for 45 per cent of recorded positive predation events. But as cats can’t tell the difference between invasive and native species, they also prey on European mantises.
A lot of the data collected for this study was made possible thanks to citizen science.
"My colleagues William di Pietro and Antonio Fasano (from the monitoring project GRIO) have managed to set up a huge citizen science project and collect over 2,300 reports. 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,” said Battiston.
Mantids are largely sit-and-wait predators, so they remain hidden and inactive most of the time – making field sampling of predator-prey interactions difficult. The researchers have highlighted that if it wasn’t for the georeferenced observations collected by the public, such a detailed look into rarely-witnessed interactions wouldn’t have been achievable.
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The researchers note that an average citizen can do more than just report sightings, too – during winter, when the trees and shrubs are bare, the mantis’ brown, spongy egg cases (which can measure 2 to 3 cm) become easy to spot.
The eggs are not dangerous, but scientists have emphasised that people should still notify a specialist before removing them as they can easily be mistaken with eggs of native mantis species.
Read the full findings here.
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Top image: Hierodula tenuidentata. Credit: DINA LUKOIANOVA/Getty Images
