Given the large number of nests found in 2025 (163), it was not feasible to complete the genetic analysis undertaken in previous years.
Instead, Defra commissioned research using an alternative genetic method, to look at relatedness between the nests found in 2025. This method used far more genetic information per hornet (a panel of some 160 Single Nucleotide Polymorphisms), but with fewer samples per nest. This gave a different type of information to previous years, with greater detail about how pairs of nests were related (including whether nests were cousins to each other). However, it did not include, in-depth investigations of the life stages present in each nest or analysis of whether a nest was offspring of a nest in 2024.
An overall conclusion from this is that all nests showed some degree of kinship to each other, as might be expected from the relatively recent origin of the European Yellow-Legged Hornet (YLH) population. Notably, some nests were far more related to each other (up to 26 potential cousin relationships to other nests) than others (only one or two potential cousin relationships to other nests). The nests which were more related to each other likely reflect UK resident breeding by YLH, including hitchhiking events/ internal movements with human transport within the UK, while the nests which were less related to each other likely reflect continuing arrival of queens from continental Europe that were able to establish nests.
The map given below shows the numbers of cousin relationships each nest had with other UK 2025 nests, where larger circles reflect nests with greater numbers of relationships than smaller ones (see key). Only a sub-set of nests are shown. As can be seen from the map, it is likely that both breeding in the UK and continuing arrivals from abroad were occurring. Results from microsatellite analysis of YLH nests destroyed before 1st October, 2025 showed that all analysed hornets were from the European YLH population and not arrivals from elsewhere. This is consistent with what was seen in previous years.
Map of Yellow-legged hornet nest connectivity 2025
Notes on methods:
The previously used analyses used a small number (15) of microsatellite markers in the nuclear genome, as described in Jones et al 2020 https://www.nature.com/articles/s41598-020-76690-2.
The current project used a large panel of Single Nucleotide Polymorphisms (SNPs) developed by a PhD student at Fera Science and Newcastle University (thesis unpublished).
Further information here on Historic UK Yellow-Legged Hornet Incursions » APHA – National Bee Unit – BeeBase
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