# Range Expansion of the Giant Water Bug Lethocerus patruelis (Stål, 1854) in Europe

## TL;DR

This study shows that the giant water bug Lethocerus patruelis is expanding its range in Europe, likely due to climate change, and could spread further in the future.

## Contribution

The study provides new insights into the range expansion of Lethocerus patruelis and its potential future spread under climate change scenarios.

## Key findings

- Lethocerus patruelis is expanding westward and southward in Italy.
- The species shows niche conservatism but also ongoing colonization.
- Suitable habitats are expected to increase under future climate scenarios.

## Abstract

Climate change is altering freshwater ecosystems, causing extinctions, range expansions, and facilitating biological invasions. Colonization by novel species can drastically affect local biodiversity, particularly in aquatic habitats.
Lethocerus patruelis
(Stål, 1854) is a large predatory aquatic insect whose distribution spans from the Balkans to south‐eastern Asia. In the last decades,
L. patruelis
sightings outside its known range have increased, particularly in Italy. The aim of this study was to assess the drivers of this expansion and the potential for future spread. We collected records of
L. patruelis
using published literature, citizen‐science platforms, and social media. These data were used to test for directional expansion and to compare historical and novel niches. Second, we used observations from the historical range of the species to create a suitability model using MaxEnt, testing it using observations from Italy. Finally, we projected the model under three future climatic scenarios to assess the potential for future expansions. We detected a significant westward and southward expansion of
L. patruelis
in Italy. Niche conservatism between historical and novel ranges was observed. Nonetheless, we found limited overlap and a high level of niche unfilling, suggesting an ongoing colonization process. The suitability model showed good predictive performance, indicating a preference toward Mediterranean climates and a selection against agricultural areas. Suitable areas were predicted to increase under all three future climatic scenarios. This study suggests an ongoing spread of
L. patruelis
and a strong expansion potential in Europe facilitated by climate change.

We modeled the expansion of the giant water bug, with a focus on niche dynamics and habitat suitability. Our results show evidence for an ongoing expansion, with strong potential for further spread under future climatic conditions.