Predation of the social wasp Polybia occidentalis (Hymenoptera:Vespidae) by the water scorpion Ranatra obscura (Hemiptera:Nepidae)

Abstract

The genus Ranatra (Nepomorpha) is a formidable predator with significant importance in trophic webs, playing a crucial role in regulating aquatic and semi-aquatic communities through population control. However, studies on the diet of Ranatra species remain scarce, particularly in poorly understood Amazonian regions such as Marajó Island. This lack of data hampers our understanding of species behavior and the development of targeted conservation actions needed to maintain the ecological balance of complex networks, especially in areas under anthropogenic threat. Our study was conducted in the municipality of Salvaterra, within the Marajó Island archipelago, where we observed predation of the predatory species Polybia occidentalis (Olivier, 1791) by Ranatra obscura Montandon, 1907. We captured the insects using a sieve in the water column of a stream, which had been previously divided into three 50-m sections. Subsequently, we monitored Ranatra's behavior during the predation event, revealing its predatory aggressiveness and hunting ability—traits often underestimated due to its piercing-sucking mouthparts. This new record enhances our understanding of the diet and natural history of Nepomorpha and Ranatra, and highlights the importance of allochthonous material for predator species, revealing their role in terrestrial and semi-aquatic ecological networks.