Colourful new species of weevil discovered in Co Down

The colourful insect, nicknamed the "Fence-climber Twiglet Weevil" due to its prevalence on wooden fences, was found in County Down by Buglife Conservation Officer Joshua Clarke, during a night-time survey in September 2022.

After the initial discovery and additional finds, Joshua partnered with Stewart Rosell, a PhD student based at Agri-Food and Biosciences Institute, to intensively search other sites with similar habitats; their efforts uncovered numerous specimens of the mysterious weevil. It was then discovered leading Irish entomologist, Dr. Roy Anderson, had independently collected specimens as early as 2011 that remained undetermined, which were later confirmed to be the same species.

To formally evaluate and describe the new species, the Northern Irish team collaborated with Dr. Peter Stüben, a leading weevil researcher at the Curculio Institute in Germany. Dr Stüben described the weevil’s morphology and provided its DNA barcode, available in the journal Weevil News.

"The distinct features, like the raised reddish-brown structure on its back called the scutellum, along with genetic analysis of its mitochondrial DNA, revealed this weevil was not closely related to any known Western Palearctic species," stated Dr. Stüben.

The new weevil has officially been named Xenosacalles irlandikos, which loosely translates as the Irish stranger weevil, reflecting that this colourful weevil probably arrived in Ireland from somewhere else.

"This discovery highlights our incomplete understanding of global invertebrate biodiversity," said Stewart Rosell. "and the challenges this creates for entomologists identifying and understanding non-native invertebrates."

Joshua Clarke added “The influx of non-native species to Ireland shows no signs of slowing down. Introductions frequently occur through the importation of plants and wood products and factors like climate change may enable introduced species to gain a foothold and proliferate in new regions.”

He continues: “This includes non-native species being described outside of their native range, such as the flatworm Marionfyfea adventor (Jones & Sluys 2016) with probable introduction from New Zealand, and Anasaitis milesae (Logunov 2024), a jumping spider with speculative origins from the Caribbean.”

The authors had speculated the weevil could be an accidental introduction from another part of the world, like Australia. After publication, they had been contacted by a Tasmanian entomologist and weevil enthusiast, Otto Bell, who recognised the species as a possible undescribed weevil specimen he and his twin brother Bruno Bell had collected in Victoria, Australia.

“We only know of several specimens of this previously undetermined species” stated Otto Bell.

Two of those specimens are available in the Tasmanian Museum & Art Gallery collections, with senior curator Dr. Simon Grove on his Facebook page saying, “these specimens were collected by Dick Bashford in 2010 on King Island as by-catch during panel traps for monitoring Ips bark beetles and remained undescribed until now”, adding “we agreed Xenosacalles irlandikos is our weevil.”

This exciting find by the dedicated Irish entomologists working together with international expertise in Germany, and now Australia, contributes to our knowledge of the varied insects present in Ireland, and provides further insight into global biodiversity. Research is currently ongoing to confirm origins, phylogeny, and ecology.