Fig 1.
Vespa tropica workers foraging.
(A) V. tropica worker attacking a small colony of a eusocial wasps (Ropalidia sp.) near Bengaluru, India (photo courtesy of V. Kumar). (B) V. tropica worker, left, compared to a giant hornet Vespa soror worker, right, on banana flowers in Hong Kong (photo courtesy of J. Yang).
Fig 2.
Detections of V. tropica nests on Guam.
(A) Number of reports made by the public of V. tropica nests, by month from 2016 to 2024 (inset: number of reports made by year). (B) A below-ground nest constructed in the buried box of an irrigation system. (C) An above-ground, exposed nest in a bamboo patch. (D) Heights of 34 above-ground nests.
Fig 3.
Reported losses of managed Apis mellifera colonies on Guam due to Vespa tropica attack.
(A) Per reporting apiary, the number of managed honey bee colonies that were considered an economic loss due to attack by V. tropica, from the first detection of V. tropica in 2016 until the end of 2024. (B) The number of colonies reported lost due to V. tropica attack out of the total number of managed hives per year (left y-axis), which yielded the percentage of managed colonies for which loss was attributed to V. tropica attack (right y-axis).
Fig 4.
Predatory behavior of Vespa tropica workers.
(A) Many beekeepers screen hive entrances to prevent hornet entry. (B) A V. tropica worker lunging at A. mellifera workers on the periphery of a bee carpet. (C) Multiple hornets attacking honey bees in a bee carpet. (D) Dead bees discarded by hunting hornets in front of a hive.
Fig 5.
Seasonal pattern of V. tropica adult activity.
Number of reports per month and year (inset) were summed across reporting constituencies. Beekeepers reported hornet sightings in apiaries to the Guam Beekeepers Association; their reports covered 2017–2024 and ranged from single and multiple-hornet attacks on colonies to no attack (e.g., flying around the apiary). Outside of apiaries, the general public reported adult hornet sightings to the Pest Hotline; those reports covered 2020–2024.
Fig 6.
Workers in A. mellifera colonies piped repeatedly during V. tropica hornet attacks.
(A) Spectrogram of A. mellifera workers piping when V. tropica attackers were hunting at a hive entrance; audio is from a cell phone recording made ~0.5 m from a hive entrance. White brackets indicate pipes that were clear enough to determine pipe duration; the red bracket indicates a series of many overlapping pipes. (B) Duration of 108 isolated pipes recorded at five hive entrances during hornet attacks.
Fig 7.
Color profiles of V. tropica hornets on Guam did not match the known color forms described across V. tropica’s native range.
Color profiles for the head+thorax and gaster were estimated for individual hornets across available specimens (images from iNaturalist.org for all native geographic regions; collected specimens and video records additionally for Guam). Within each native region, color forms adhered to Archer’s [33] descriptions. The number of records (and percentage of total) are given for each combination of colors that was observed for either the head+thorax or gaster in a geographic location (row).
Fig 8.
Color forms across V. tropica’s native range compared to hornets from Guam.
The map shows locations where community scientists have photographed V. tropica hornets, affirming its described native range [33] and presence on Guam (based on 2,112 research-grade observations from iNaturalist.org, accessed on July 17, 2025 [46]). Examples of seven V. tropica color forms, detailed by Archer [33], are shown (black-bordered images, with arrows to sites), as well as a pinned worker from Guam (red-bordered image, with a circle showing Guam). Top row, left to right: Indian-Chinese forms from India and Hong Kong (haematodes); northern Philippines form (deusta); southern Philippines and Palawan form (anthracina). Bottom row, left to right: Andaman form (eulemoides); Malayan form (leefmansi); Java and Bali form (tropica); Sulawesi-New Britain form (trimeres). The Buruan form (unicolor), indistinguishable from the southern Philippines form and lacking iNaturalist records, is not depicted. Hornets on Guam were variable, with most color profiles intermediate between haematodes and leefmansi. Photo credits clockwise from top left: SA Kajawe; YC Tam; F Botial-Jarvis; L Chen; GW Otis and S Paiero; F Botial-Jarvis; G. Cahyadi; GC Weei; J Meyer. The map was generated using QGIS Geographic Information System, whose world map is licensed under the Creative Commons Attribution–Share Alike 3.0 license (CC BY–SA). The authors specify that this figure, with our addition of V. tropica location data, is licensed under CC BY 4.0.
Fig 9.
A Vespa mandarinia adult was recently intercepted by the Port Authority of Guam.
A dead female giant hornet was discovered by an Environmental Compliance Specialist in a cargo container on October 18, 2023. A live inseminated gyne could found an entire colony.