In recent weeks, residents of Belfast have reported thousands of invasive ash sawfly larvae raining down from ash trees across the city, especially in the Twinbrook area. Known for their striking lime-green hue, these caterpillars have become a significant concern as they voraciously feed on the leaves of ash trees—one of Ireland's most common hedgerow trees, second only to hawthorn. The larvae's feeding habits can lead to complete defoliation, ultimately stunting the growth of these vital trees. Ash trees are not only crucial for local wildlife but also play a role in traditional crafts, being used to make items like hurls.

Michael McCorry, the community outreach projects coordinator for Belfast City Council, observed a sudden explosion in the caterpillar population this year. “I noticed one tree last year in Twinbrook, but this year there’s about 20 trees – it has really exploded,” he remarked. He further described how children in the area have found themselves covered in the crawling creatures as they drop from the trees. While some of the caterpillars have fallen prey to local birds, McCorry noted that the predation has not significantly reduced their numbers.

Dr. Archie Murchie from the Agri-Food and Biosciences Institute (AFBI) explained that the ash sawflies are "eating machines" thriving in Belfast's environment due to the absence of their natural predators and parasites. This particular invasive species, which was first recorded in the Belvoir estate in 2016, is believed to have spread from Scotland during an outbreak in Aberdeen. The larvae’s incredible growth rates have been exacerbated this year by an unusually warm and dry spring, accelerating their life cycle and resulting in rapid defoliation.

Monitoring of ash sawflies has been ongoing since their introduction to Northern Ireland, with specialists like Dr. Florentine Spaans noting that they have also been discovered in regions such as County Meath and Dublin. The lack of predators in their new environment has allowed the population to thrive unchecked. Dr. Spaans suggested that the sawfly larvae typically come from infected foliage that can be inadvertently transported by people. “Somebody could have got in the car at the wrong time, taken a bunch of flies with them and then crossed in the ferry and arrived in Belfast – as easy as that,” she explained.

Although the infestation can lead to significant leaf loss, the long-term impact on tree health remains uncertain. Research indicates that while repeated annual damage could diminish tree vigour, strong and healthy specimens might withstand these assaults for years. Presently, experts advise against chemical interventions, instead recommending monitoring and manual removal of the larvae as strategies to mitigate the issue.

The rapid spread of the ash sawfly, combined with existing threats such as ash dieback disease—which has been affecting Ireland’s ash tree population since 2012—presents a multifaceted challenge for the future of these iconic trees. As urban areas like Belfast encounter this invasive species, the urgency for continued monitoring and understanding of these outbreaks grows, heralding a potential shift in the ecosystem balance that could leave lasting effects on the landscape.

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Source: Noah Wire Services