AsianScientist (Nov. 27, 2025) –Ecologists often cite a straightforward rule known as the ecological competitive exclusion principle: two species that rely on the same food resources should not be able to coexist indefinitely. Sooner or later, one is expected to outcompete the other. Yet in many urban areas of central Japan, two apex insect predators—the yellow-vented hornet (Vespa analis) and the Japanese yellow hornet (Vespa simillima)—manage to coexist.
These hornets share nesting sites, foraging periods, and general behaviours, making their coexistence in cities somewhat unexpected. With urbanisation reducing prey diversity and simplifying habitats, the assumption would be that competition between them should intensify rather than ease. This contradiction prompted researchers at Kobe University to investigate the specific mechanisms that allow both species to thrive amidst the increasing ecological pressure.
Because visually tracking the feeding habits of hornets is extremely difficult, the team employed DNA metabarcoding, a technique that extracts and analyses genetic material from hornet larvae gut contents, to identify the prey species consumed. They combined this dietary information with detailed mapping of urban land cover within 500 metres of the nest sites, corresponding to the hornets’ typical daily foraging range, to explore how urbanisation influences predator diets.
The study, published in Entomologia Generalis, identified over 150 prey species across various insect orders, highlighting the complex food webs affected by urban habitat simplification. Statistical models showed that prey species richness declined sharply as developed land increased, forcing predators to adjust their hunting preferences.
Interestingly, the two species responded differently to urban pressures. The Japanese yellow hornet, usually a flexible generalist, focused on its preferred soft-bodied prey such as crickets and moths. Its diet became less diverse, but remained consistent, suggesting a strategy that prioritises nutritional quality over opportunistic feeding. In contrast, the more dominant yellow-vented hornet shifted its diet dramatically in urban areas, preying on tougher insects like beetles and other wasps. The researchers suggest that urban simplification makes these surface-active insects easier to find, even though catching them can be more challenging.
In non-urban areas, the two species consumed similar prey, reflecting their natural competitive relationship. “These patterns surprised us because the yellow-vented hornet usually displaces the Japanese yellow hornet in sugar-feeding experiments and is thus considered more competitive,” said lead entomologist Saga Tatsuya. Instead, it adjusted its diet more drastically, showing that flexibility can matter more than dominance under stress.
The results challenge the assumption that generalist predators automatically resist environmental changes. The study shows that urbanisation forces species towards dietary divergence and niche specialisation, allowing similar species to coexist by partitioning resources differently. “These changes show that cities act as trait filters that drive niche differentiation by selecting on traits that confer resilience under stress,” explained Saga.
DNA analysis also revealed a significant consequence of urban pressure. The Japanese yellow hornet DNA appeared frequently in the gut contents of yellow-vented hornet larvae. It suggests that in cities, the dominant hornet may engage in intraguild predation—hunting or scavenging its competitor—to cope with limited resources.
“The study highlights hornets as important ecosystem regulators, not just pests,” Saga noted. It offers a transferable framework for studying how central-place foragers adapt to rapid urbanisation. The key to surviving urban stress appears to be behavioural flexibility, which is the ability to radically switch prey, rather than a generalist diet.
The researchers point to the importance of investigating whether these dietary adjustments persist throughout the year and how they impact colony fitness. They emphasise the need to combine advanced techniques like DNA analysis with behavioural studies and environmental sampling to shed light on how urban forces alter food webs over time.
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Source: Kobe University; Image: Shutterstock
This article can be found at: Urbanization reduces prey diversity and promotes dietary divergence in sympatric hornet species
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