Reintroducing a nationally extinct predator, the forest caterpillar hunter (Calosoma sycophanta), for biocontrol of the invasive oak processionary (Thaumetopoea processionea) in Britain: considerations, benefits and risks

Kyle Alexander Miller , Jordan Patrick Cuff, Katiana Saleiko, Max Blake

1. Controlling invasive species remains one of the greatest challenges of the 21st century. Sustainably managing invasive pests like the oak processionary moth (Thaumetopoea processionea; OPM), which lacks natural enemies in Britain, may require the introduction, or reintroduction, of suitable biocontrol agents.
2. The forest caterpillar hunter (Calosoma sycophanta; FCH) is thought to have been historically native to Britain but is now possibly nationally extinct. A voracious predator of caterpillars, FCH could be an effective biocontrol agent of OPM, but we must first understand its ecology and natural history, which is scarcely recorded in patchy literature from the past century.
3. Here, we conducted a systematic review to inform a wider synthesis on the status of FCH in Britain and Europe, its known trophic interactions and habitat preferences, and the influence of climate on its current and future distributions. This informed discussion of the risks and benefits of reintroducing FCH to Britain.
4. Based on the records available, we stipulate that translocation of FCH populations to Britain should be based on the cautious assumption that it is a reintroduction following national extinction, likely due to poor prey availability. The biocontrol of various pest species by FCH, including OPM, is likely, and the suitability of Britain’s climate may increase.
5. Reintroduction of FCH to Britain could aid management of OPM whilst also returning an important invertebrate predator to British forests. Further evidence of the wider direct and indirect interactions of extant FCH populations elsewhere, and deeper investigation into FCH’s habitat requirements, are, however, required to safeguard the success and sustainability of prospective reintroduction.