The question of invasiveness matters because the terms alien and invasive are often used interchangeably, yet they carry very different regulatory weight. Under EU regulations and IUCN protocols, an alien species that simply appears in new localities is not automatically a cause for alarm. Only when a species causes serious adverse impacts on biodiversity, ecosystem services, or social and economic interests can it be classified as invasive, a status granted to roughly 10 to 15 percent of alien species in Europe. Until now, the impacts of alien mantises on native ecosystems have been poorly understood, with studies so scarce that biocontrol regulations, public communication, and conservation planning have all been hampered. The new research set out to close that gap by quantifying reproduction, testing chemical attraction between species, and cataloguing real-world interactions across Italy.

The laboratory results on reproduction are striking. Oothecae, the foam egg cases that mantises produce each autumn, were collected from two Northern Italian populations around Castel Goffredo and Milan, roughly 120 kilometers apart, and incubated under controlled conditions. When nymphs emerged the following April, the researchers counted a total of 3,133 individuals, averaging 209 hatchlings per ootheca, with individual cases producing between 101 and 304 nymphs. That figure is roughly double the productivity documented for the native European mantis, Mantis religiosa, which averages about 127 nymphs per ootheca. Equally important, the young nymphs showed remarkably low cannibalism rates during their first weeks of life, even at high densities and in the absence of prey. Low early cannibalism means that crowded urban environments, where many hatchlings may emerge in a single garden or park, can still support rapid and competitive population growth.

Reproductive output alone does not make a predator damaging, but the behavioral experiments revealed a second, more insidious mechanism. In a purpose-built arena with four tubes carrying different airborne cues, the researchers tested whether male Mantis religiosa could distinguish the pheromones of females of their own species from those of Hierodula females. Over 50 trials, monitored by roughly 30,000 time-lapse photographs, the males spent 73.8 percent of their away-from-center time heading toward females rather than toward food or empty controls. Nearly 40 percent of those choices favored conspecific females, but 34.2 percent led the males toward Hierodula females, a statistically insignificant difference from their response to their own species. The pheromone signals of the two genera appear almost interchangeable to native males, a weakness with potentially serious evolutionary consequences.

The consequences became lethal when the barriers were removed. In follow-up trials inside a large mesh container, all five Mantis religiosa males that approached Hierodula females were captured and devoured. The researchers describe this as a fatal attraction, closely paralleling a phenomenon documented in New Zealand, where males of the endemic Orthodera novaezealandiae are lured to their deaths by the pheromones of the alien Miomantis caffra. Because mate-searching males are the most mobile stage of a mantis life cycle, even a modest rate of heterospecific misorientation could translate into substantial extra mortality, skewing the operational sex ratio of native populations and depressing fertilization success wherever the two genera coexist. Notably, most of the misdirected males in the tests preferred Hierodula patellifera over H. tenuidentata.

The citizen science records painted a broad picture of what these predators actually eat. Of 2,393 general observations submitted to the Italian project Progetto Mantidi Aliene between June 2020 and December 2024, 86 documented direct interactions with other species. Fifty-three of these, or 62 percent, were negative interactions in which Hierodula preyed on native animals, while 31 documented predation on the mantises themselves and two were cases of Hierodula cannibalism. Among the prey, hymenopterans dominated, accounting for 43 percent of negative interactions, followed by true bugs, mantises, flies, butterflies, grasshoppers, and damselflies. Adults took large and even hazardous prey, including hornets, paper wasps, cicadas, the Egyptian locust, and the invasive brown marmorated stink bug, while nymphs concentrated on smaller insects such as flies and honey bee workers. Every recorded interaction occurred in urbanized settings such as gardens, parks, and balconies.

The most alarming records involved vertebrates. Four documented cases showed adult Hierodula females preying on common wall lizards, Podarcis muralis, and a late-instar nymph capturing an Italian tree frog, Hyla perrini. Both species are listed in Annex IV of the EU Habitats Directive, meaning they enjoy strict legal protection. Although vertebrate predation is clearly rare, the ability of large female mantises to subdue amphibians and reptiles raises the specter of spillover into fragmented or insular habitats harboring micro-endemic herpetofauna. A recent August 2024 sighting of Hierodula on the island of Elba, home to a distinct local subspecies of the wall lizard, illustrates the risk, and the researchers flag the Aegean islands, where the mantises have been recorded since 2012, as an urgent priority for assessment before impacts on delicate island ecosystems become irreversible.

Hierodula is not without enemies, but the study found the resistance to be strikingly one-sided. Hornets, particularly the European hornet Vespa crabro, emerged as the principal natural predators of the alien mantises, taking both nymphs and adults, while domestic cats accounted for 45 percent of recorded vertebrate predation on Hierodula, with golden orioles, little owls, great spotted woodpeckers, and blue tits also involved, the latter two birds carrying off entire oothecae. Stink bugs were observed piercing mantis egg cases with their rostrums, and native Crematogaster scutellaris ants nested inside hatched oothecae. Crucially, no instance of native mantids feeding on Hierodula was ever recorded, suggesting weak top-down resistance in the recipient community. The researchers liken this pattern to the harlequin ladybird, another generalist invader whose European success has been attributed partly to limited natural enemy pressure combined with aggressive predation on native competitors.

Human-modified environments appear to be the launchpad for the invasion. All recorded interactions occurred in urban or suburban settings, and the mantises have been observed using artificial refuges, including hunting directly over an insect hotel in a private garden, and exploiting city heat islands to prolong their activity into colder months. This adaptability, combined with broad trophic generalism and high fecundity, mirrors the trajectory of the Chinese mantis in North America, where Tenodera sinensis has repeatedly been shown to depress populations of the smaller native Carolina mantis through both competition and direct predation. The authors caution that their competition tests were conducted under artificial conditions and that niche separation, with the tree-dwelling Hierodula favoring shrubs and foliage while Mantis religiosa keeps to low grasses, may moderate interactions in natural habitats. In heavily anthropized landscapes, however, such separation is not always possible.

The study concludes that the two Asian mantises satisfy four of twelve IUCN criteria for invasive species: exceptionally high reproductive output, demonstrable reproductive interference with a native mantis, extensive predation on native vertebrates and pollinators, and exploitation of anthropogenic habitats. The scale of the impacts still requires further investigation, but the authors urge management to move beyond passive monitoring. Their recommendations include detailed risk assessments using predictive models, targeted surveillance in areas hosting endemic or threatened vertebrates and sensitive pollinator networks, and public communication discouraging the deliberate relocation of individuals or oothecae, with removal under specialist guidance encouraged instead. They also note that parasitoid wasps of the genus Podagrion, known to attack Hierodula egg cases in their native range and already present in Europe, may emerge as future limiting factors. Acting promptly, they warn, is essential before these formidable generalists inflict deeper damage on European ecosystems.

Subject of Research: First measured impacts of the alien mantises Hierodula tenuidentata and Hierodula patellifera on European biodiversity

Article Title: Call me invasive: Testing the first impacts of the alien mantises Hierodula patellifera and Hierodula tenuidentata on European biodiversity

Article References: Battiston, R., Di Pietro, W., Boscato, F., & Fasano, A. (2026). Call me invasive: Testing the first impacts of the alien mantises Hierodula patellifera and Hierodula tenuidentata on European biodiversity. Journal of Orthoptera Research, 35(1), 179-190. https://doi.org/10.3897/jor.35.165233

Image Credits: AI Generated

DOI: 10.3897/jor.35.165233

Keywords: invasive species, Hierodula tenuidentata, Hierodula patellifera, Mantis religiosa, predation, pheromone attraction, citizen science, pollinators, reproductive interference, European biodiversity, oothecae, urban ecology