… a blog by Karim Vahed, England Manager for Buglife and member of the England Species Reintroduction Task Force.
Conservation translocations are the deliberate movement and release of individuals of a species into the wild for conservation purposes. Given the stories that make the headlines, you would be forgiven for thinking that conservation translocations in Britain are almost entirely about the feathered and furred, such as Beavers, Pine Martens and birds of prey- and that they are something new. Invertebrates, in comparison, have received little attention, yet there is a history of invertebrate conservation translocations in Britain that spans over half a century and covers a multitude of diverse species.
National reintroductions
The stories that receive media attention often involve the translocation of large animals over large distances, crossing country boundaries. There are some invertebrate examples that do involve large scales: the Large Blue Butterfly (Phengaris arion) in the 1980s and early 1990s, and the Chequered Skipper (Carterocephalus Palaemon) from 2018, were both successfully reintroduced to England from surviving populations in mainland Europe. Perhaps due to the small size of invertebrates, however, the majority of invertebrate conservation translocations in the UK have involved a much smaller scale, using individuals from donor populations within the region.
Local reintroductions
Such local reintroductions have included Field Crickets (Gryllus campestris) and Wart-biter Bush-crickets (Decticus verrucivorous) since the 1990s, Barberry Carpet Moths (Pareulype berberata) in the 1990s, Marsh Fritillary Butterflies (Euphydryas aurinia) from 2005, Freshwater Pearl Mussels (Margaritifera margaritifera) from 2007, Fisher’s Estuarine Moths (Gortyna borelii lunata) from 2008, Fen Raft Spiders (Dolomedes plantarius) from 2010-2015, Southern Damselflies (Coenagrion mercurial) from 2009, White-faced Darter Dragonflies (Leucorrhinia dubia) from 2010, Large Marsh Grasshoppers (Stethophyma grossum) from 2018, Pine Hoverfly (Blera fallax) from 2018, Pond Mud Snails (Omphiscola glabra) from 2019, Dark-bordered Beauty Moth (Epione vespertaria) from 2022, Medicinal Leech (Hirudo medicinalis) from 2023, and Tadpole Shrimp (Triops cancriformis) from 2023.
In fact, translocation projects involving Netted Carpet Moth (Eustroma reticulatum) 2006-2008, Ladybird Spider (Eresus sandaliatus) since the mid-1990s, and Narrow-headed Ant (Formica exsecta) since 2017, have all involved the movement of individuals from donor populations to new receptor sites within the same county (Cumbria, Dorset and Devon, respectively). In the case of the Narrow-headed Ant, the distances involved in translocations have been as little as 400 m. In these instances, the small and isolated nature of the key microhabitats, combined with the low mobility of the species means that natural colonization of suitable habitat would have been very unlikely.
Conservation rearing
In some cases, ex-situ conservation rearing can be a useful way of boosting the number of individuals for release. Arguably, the small size of invertebrates and the high reproductive potential of some species, makes this approach more cost effective than in most mammals or birds. Conservation rearing has played an important part in at least fifteen of the above translocation projects. Collaboration between zoos can make this particularly effective: at least ten different zoos and aquaria, for example, collaborated from 2010-2015 to rear thousands of Fen Raft Spider spiderlings, which were released to establish four new populations in Norfolk and Suffolk. Incidentally, the response of the media to news of the success of some of these populations in 2024 was disappointing. Several tabloids ran with headlines such as ‘Spiders the size of rats invade UK in their thousands as homeowners given urgent warning’!
For a few invertebrate species that are relatively easy to rear, citizen science has had a role to play in the process. Buglife’s Marvellous Mud Snails Cornwall project involved local schools, colleges and volunteers in rearing the Pond Mud Snail in small aquaria, following the success of a similar project in Scotland. This resulted in the release of around 500 snails at four new sites in Cornwall. Similarly, Citizen Zoo’s Hop of Hope project has seen the release over 6,000 Large Marsh grasshoppers to new sites in Norfolk. These were reared by 47 volunteers.
A long and complex life cycle doesn’t necessarily preclude conservation rearing. That of the Freshwater Pearl Mussel, for example, involves tiny larvae called glochidia, which need a salmonid fish host in order to survive to the next stage. The mussels are very long-lived and take many years of rearing until they are large enough to be released. Despite this, the Freshwater Biology Association have been able to rear over 50,000 individuals in specialised facilities since 2007 and have recently begun to release hundreds of juvenile mussels to reinforce ageing populations in Northern England.
Assisted colonization
The conservation translocation examples covered so far have focused on reintroduction (translocation of an organism within its natural range to an area from which it has been lost) and, in the case of Freshwater Pearl Mussels, reinforcement (translocation of individuals into an existing population). There are other forms of conservation translocation however, such as assisted colonisation. This is the translocation of an organism to benefit the conservation status of the focal species outside of its natural range. From 2000, Stephen Wills and colleagues from Durham University introduced Marbled White Butterflies (Melanargia galathea) and Small Skippers (Thymelicus sylvestris) into two sites in northern England, beyond their northerly range margins, to sites that were predicted to have become climatically suitable. Nine years later, Wills and colleagues reported that both populations were doing well.
Ecosystem services
A further reason for conservation translocations is to introduce a species to an area due to the role it plays within the ecosystem. Invertebrates provide a wide range of ecosystem services, including pollination, decomposition and nutrient cycling, predation of pest species, water purification and many others. Forestry England, for example, are looking at the feasibility of translocating the Wood Ant (Formica rufa) which are regarded as a keystone woodland species, to woodlands where they are currently absent, such as Kielder Forest in Northumberland.
Rescue
The case of White-clawed Crayfish (Austropotamobius pallipes) illustrates a further reason for conservation translocations: rescuing populations in immediate danger. For the last few decades, numerous projects across the UK have focussed on translocating individuals from populations at immediate risk from the invasive North American Signal Crayfish (Pacifastacus leniusculus) to safe ‘ark sites’. The Signal Crayfish both outcompetes the native species and carries a fungal ‘Crayfish Plague’, to which White-clawed Crayfish are particularly susceptible.
What makes a successful reintroduction project?
Although invertebrate conservation translocations may often be logistically easier than those involving mammals and birds, they still need to be planned rigorously, following the appropriate guidelines (e.g., see Reintroductions and conservation translocations in England: code, guidance and forms – GOV.UK). A key consideration, particularly with reintroductions, is understanding why the species is no longer at a site. If that is because site conditions have changed, putting in place habitat management to reverse those changes before a reintroduction is undertaken will be crucial. Indeed, a key factor in the success of all of the above conservation translocations has been the restoration of natural habitat, linked with a detailed knowledge of the micro-habitat requirements of each stage of the species’ life cycle. It is worth noting here that conservation translocation is just one element of the conservation tool kit; in many cases targeted habitat restoration and management alone can allow species to recover, especially for more mobile species. Another notable feature of successful projects has been close collaboration between a wide range of stakeholders, including Natural England, species specialists, eNGOs, landowners and the public.
We also have a lot to learn from cases in which conservation translocations have been unsuccessful, although such cases are even less likely to be publicised. A lack of genetic diversity in donor stock may have contributed to the lack of success of initial attempts to reintroduce the Short-haired Bumblebee (Bombus subterraneus) in the 2010s. On the other hand, Paul Waring in 2004 proposed that sub-optimal management of Barberry bushes was the reason for the failure of populations of Barberry Carpet Moth to establish at one site, despite the release of thousands of caterpillars in multiple attempts.
Why should we raise the profile of invertebrate reintroductions?
Given the range of examples of successful invertebrate conservation translocation projects, it is perhaps surprising that they receive so little attention in comparison with their feathered and furred relatives. But does that really matter? Unfortunately, I think it does, because people will only care about what they know about. And what people care about will ultimately influence the allocation of conservation funding. A study by Benoit Guénard and colleagues, published in 2025 (see Limited and biased global conservation funding means most threatened species remain unsupported | PNAS), revealed that 80% of global conservation funding goes to vertebrate species and just 6% to invertebrates, despite the imbalance in species numbers being precisely the opposite pattern. So, while recent news of the change in legislation that now allows beavers to be released into the wild in England is a great conservation success worth celebrating, we must make more effort to ensure that conservation translocations of invertebrate species receive a similarly high profile.
Main Image Credit: Wart-biter Bush-cricket (Decticus verrucivorus) © Dr Sarah Henshall