Yellow-Legged Hornet (YLH) is native to the tropical and subtropical areas of Southeast Asia. This wasp was first reported to the Georgia Department of Agriculture (GDA) in Savanah GA by a beekeeper. On August 9, 2023, APHIS confirmed it as a yellow-legged hornet. Later they found several nests of YLH in the area and were able to successfully eradicate them. This is the first report of YLH in the United States.
YLH is a social wasp species that constructs a large paper nest above ground, particularly in trees and man-made structures like eves on roofs. As the colony grows, the nests can house up to 5000 – 6000 workers on average.
YLH nest (Location unknown)
Don’t confuse YLH with the ‘northern giant hornet’ (Vespa mandarinia), formerly called ‘Asian giant hornet’. V. mandarinia was first reported in the US, in Fall 2019 from Blaine, Washington. So far, this species is not considered established in the US (Tripodi A, Hardin T. 2020).
Quick size comparison of a few wasps and hornets common to western and north-eastern US, from left to right - 1. yellow-legged hornet (Vespa velutina), 2. eastern yellow jacket (Vespula maculifrons), 3. European hornet (Vespa crabro), 4. Northern paper wasp (Polistes fuscatus), 5. eastern cicada killer (Sphecius speciosus), 6. northern giant hornet (Vespa mandarinia), 7. western cicada killer (Sphecius grandis).
YLH is about 2.5 cm long and smaller than the European hornet (Vespa crabro). The queen is about 30 mm and males and workers are about 24 and 20 mm in length respectively. A distinct character to separates them from other hornets is the yellow tarsi. The head from above is black but can be yellow in different subspecies. 10 subspecies have been identified worldwide (Nguyen et al., 2006). While the subspecies nigrithorax du Buysson (1905) is invasive in Europe (More Info), the subspecies reported in the USA are unknown.
Vespa velutina subspecies nigrithorax - adult worker showing characteristic identification features.
Left, YLH nest recorded in France (Monaceau et.al., 2014) and Right, YLH attacking a honey bee
Are they recorded anywhere else?
Yes, YLH was first reported in France in 2004, and has since established in other parts of Europe (Monaceau et.al., 2014).
The first record of the hornet as far north as Ireland was in April 2021. Most interestingly, in the molecular analysis of CO1 (Cytochrome Oxidase 1) gene, the entire range of YLH in Europe converged to a single mated queen arriving from China some 15-20 years ago, which has expanded since the first recorded YLH in France. These data show the potential for exotic insects to establish and spread with very few or single individuals (Dillane et.al., 2022).
After the first report in Georgia in August 2023, YLH was reported in Jasper County, South Carolina on November 2023. So far this species has been reported only in these two US states. Although several authors indicate that it is unlikely YLH will be established in the US, (More Info.) it is important to be vigilant as we are experiencing warmer weather patterns globally.
Are there ecological or economic impacts?
Yes. YLH feeds on honey bees as well as other insects. During the summer, YLH will hunt foraging honey bee adults and invade honey bee colonies to steal the larvae. This is a great threat to local honey bee and native bee populations in the US (Read more).
Studies indicate that approximately 30% of the honey bee hives in France are being attacked and weakened. Also, the same study showed the diet of YLH is composed of almost 70% of honey bees and other similar species (Apoidea) in certain areas (Monaceau et.al., 2014).
YLH life cycle in temperate climate
When a fertilized queen emerges after surviving the winter, the queen feeds on sap, develops her ovaries, and looks for a suitable nesting site in the spring. In Ireland, it was found that 99% of queens don’t survive the winter, but often 1 queen is enough to start the population.
Once the queen selects a suitable site, she alone is responsible for building a ‘primary nest’ close to the ground, foraging for resources, laying eggs (around April), and caring for the young. Emerging workers from the ‘primary nest’ (females – usually emerge in June) assume all duties outside of the nest, including building a ‘secondary nest’ (typically oval and found high up in trees and buildings) and feeding the young in the spring. The queen moves to the 'secondary nest' and keeps laying more eggs. YLH adults feed on sugary substances, but, they prey on other insects especially honey bees to provide proteins necessary for the development of the broods.
When temperatures start to peak in summer-early fall, the colony begins producing males and the next year’s queens. At this time workers attack more honey bee hives, killing all the adult bees to obtain food with higher protein content for these developing reproductive castes. Then the hornets remove the hive’s brood, taking bee larvae and pupae back to their nests to feed the young.
Nest size peaks in September to October and can have 6000 workers on average including 200-500 future queens. At this time, the queen produces males and they leave the nest before the next year queens emerge. Male YLHs locate and mate with the new queens, which is their only function in the colony.
After mating, queens will spend the colder months overwintering in a sheltered spot and the cycle continues (De la Hera et. Al., 2023, Monceau et al. 2014 and https://invasives.ie/species-alerts/asian-hornet/ ).
Control
Control methods currently used to limit the impact of this hornet include trapping, physical protection of the apiaries using nests, and hornet nest destruction using chemicals or sulfur dioxide (gas) (This needs to be done by professionals). The direct nest destruction methods by insecticide or gaseous sulfur injection in the nest are efficient, but at the same time, can impact non-target beneficial insects, have side effects on the environment, and cause respiratory problems in humans. The biggest problem is locating the nests early in the season before predation on honey bee hives. These control methods are hampered by the colonies being discrete, numerous, often not accessible, and well-hidden mostly in the foliage of trees (Poidatz et al., 2018).
Apart from insecticides and nest removal, some countries in Europe use ‘tailored trapping’ of the hornet to decrease their population by using sugar bait in winter and protein bait in the summer. However, Rojas-Nossa et. Al., 2023 showed that trapping needs to be used more carefully as this baited trapping method is an added threat to the native biodiversity – ‘See how this trap works here’
According to a 2020 study in Korea, the larvae of YLH could be a potential human food source, similar to the larvae of the Northern giant hornet (Vespa mandarinia), which are a Japanese delicacy (Jeong et. Al., 2020).
Reporting tools
Reporting YLH in SC - Click here to log details.
Report YLH in GA - Click here to log details.
Outside of Georgia, please contact your state plant regulatory official, here . If it is safe to do so, take a photo or collect a dead specimen of the pest to help experts identify the insect.
OH, residents can contact The Ohio State University's Entomology Department or Plant and Pest Diagnostic Clinic (PPDC) via email (ppdc@osu.edu, or entomology@osu.edu) or send specimens or photographs to PPDC. Details on how and where to send specimens and images can be found here.
References
De la Hera, Omaira, María Luz Alonso, and Rosa María Alonso. 2023. "Behavior of Vespa velutina nigrithorax (Hymenoptera: Vespidae) under Controlled Environmental Conditions" Insects 14, no. 1: 59. https://doi.org/10.3390/insects14010059
Dillane E, Hayden R, O'Hanlon A, Butler F, Harrison S (2022) The first recorded occurrence of the Asian hornet (Vespa velutina) in Ireland, genetic evidence for a continued single invasion across Europe. Journal of Hymenoptera Research 93: 131-138. https://doi.org/10.3897/jhr.93.91209
Jeong, Hyeyoon; Kim, Ja Min; Kim, Beomsu; Nam, Ju-Ock; Hahn, Dongyup; Choi, Moon Bo (July 2020). "Nutritional Value of the Larvae of the Alien Invasive Wasp Vespa velutina nigrithorax and Amino Acid Composition of the Larval Saliva". Foods. 9 (7): 885. doi:10.3390/foods9070885. ISSN 2304-8158. PMC 7404655. PMID 32640612.
Monceau K, Bonnard O, Thiéry D. 2014. Vespa velutina: A new invasive predator of honeybees in Europe. Journal of Pest Science 87: 1-16. DOI:10.1007/s10340-013-0537-3
Nguyen LTP, Saito F, Kojima J, Carpenter JM, 2006. Vespidae of Viet Nam (Insecta: Hymenoptera). 2. Taxonomic notes on Vespinae. Zoological Science, 23(1):95-104. http://zsj.jstage.jst.go.jp/
'Northern Giant Hornet’ Adopted as Common Name for Vespa mandarinia https://www.aphis.usda.gov/aphis/ourfocus/planthealth/plant-pest-and-disease-programs/honey-bees/agh/asian-giant-hornet
Poidatz. J, R. López Plantey, D. Thiéry, 2018. Indigenous strains of Beauveria and Metharizium as potential biological control agents against the invasive hornet Vespa velutina,. Journal of Invertebrate Pathology, Volume 153, Pages 180-185, ISSN 0022-2011, https://doi.org/10.1016/j.jip.2018.02.021.
Rojas-Nossa SV, Mato S, Feijoo P, Lagoa A, Garrido J. Comparison of Effectiveness and Selectiveness of Baited Traps for the Capture of the Invasive Hornet Vespa velutina. Animals (Basel). 2023 Dec 29;14(1):129. doi: 10.3390/ani14010129. PMID: 38200860; PMCID: PMC10778013.
Tripodi A, Hardin T. 2020. New Pest Response Guidelines. Vespa mandarinia Asian Giant Hornet. United States Department of Agriculture. (13 April 2020)
Vespa velutina in APHIS web site- https://www.aphis.usda.gov/aphis/ourfocus/planthealth/plant-pest-and-disease-programs/honey-bees/yellow-legged-hornet
Vespa velutina in CABI Digital Library -https://www.cabidigitallibrary.org/doi/10.1079/cabicompendium.109164
