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Rosemary Beetle Spotted in Northern England Gardens: A New Invasive Threat
By Drooid · · How we work
A Shimmering New Visitor
A garden diarist in the North Pennines reported finding a brightly coloured beetle among rosemary leaves in an herb bed. The insect, identified as the rosemary beetle (*Chrysolina americana*), displays purple-green striped elytra and is native to the Mediterranean. Its appearance in a UK garden signals a potential expansion of this non-native species.
Background and Spread
*Chrysolina americana* was first recorded living outdoors in the United Kingdom in 1994. Since then, observers note a rapid increase in its presence, which the diarist attributes to a warming climate that creates milder winters and longer warm periods. The beetle’s short wings limit its flight range, suggesting that human-mediated movement of plants may aid its spread.
Threat to Lamiaceae Herbs
Both adult beetles and their grey, longitudinally-striped larvae feed on the foliage of plants in the Lamiaceae family. The diarist observed damage to lavender, sage, thyme and rosemary, noting that the beetles can strip plants to bare stems, leading to die-back. Adults tend to congregate on lavender seedheads rather than flowers, and they drop from stems when disturbed, making detection difficult.
Monitoring and Management Advice
The Royal Horticultural Society (RHS) is actively monitoring the beetle’s distribution and has called for public sightings to track its spread. RHS guidance recommends hand-picking adults and larvae where feasible and tolerating their presence “where possible” as a colourful addition, though the advice acknowledges the risk to herb crops. The diarist’s observations underscore the need for early detection, especially in frost-hollow gardens that may provide the mild conditions the beetle requires to survive winter.