The Tansy beetle (Chrysolina graminis) is a beautiful iridescent green leaf beetle, identifiable by their distinct coppery sheen. Measuring roughly just 1 cm in length, they are around a quarter of the size of a 1 pence coin. These beetles are specialist herbivores, mainly feasting on Tansy plants (Tanacetum vulgare), a perennial herb which is often found beside riverbanks or in wetlands. They rely on these plants to complete their entire life cycle on and around.
Adult Tansy beetles are active around the tops of the plants from April until June, where they feed, mate, and lay eggs. The eggs hatch between May and July into larvae, which then also feed on Tansy leaves. The larvae eventually burrow underground at the base of the Tansy plants and spend the winter there, until emerging as adults in April of the following year.
The Tansy beetle was once widespread in wetland areas across the UK, but they are currently listed as an endangered species, not just in the UK but across its worldwide range. They are now only found along the banks of a 30km stretch of the River Ouse around York, with a much smaller population recently discovered in Cambridgeshire. The decline in Tansy Beetle populations has led to its designation as a UK Biodiversity Action Plan (UKBAP) priority species in England (section 41 species), which means that public bodies have a duty to protect it, together with its habitat.
Although the Tansy plant is widespread along the River Ouse, land-use changes and the increase of invasive species have resulted in a decline in plants over the past few decades. As the beetles are dependent on Tansy plants as their sole food source, if a clump disappears, the beetles have to walk to a new patch as they very rarely fly. This has had an adverse affect on Tansy beetle numbers, as their populations have become increasingly isolated.
The conservation of this threatened species is steered by the Tansy Beetle Action Group (TBAG), a collaboration of local and national organisations seeking to save the species and support a more resilient habitat.
TBAG was set up in 2008, to initiate and oversee conservation efforts aimed at saving the Tansy beetle from extinction in the UK.
Alongside volunteers from The Deep, the group comprises representatives from Askham Bryan College, BIAZA (British and Irish Association of Zoos and Aquariums), Buglife, Carstairs Countryside Trust, City of York Council, Environment Agency, National Trust, Natural England, Species Recovery Trust, St Nicks, University of York, Wildfowl and Wetland Trust and York Natural Environment Trust.
Together, the group is working to a five year conservation plan for the beetle.
Thanks to funding from the National Lottery Heritage Fund, the Ernest Cook Trust, SITA Trust, York Business ‘Sumptuosity’ and a legacy donation, these conservation efforts have been made possible.
Volunteers from TBAG have been continuously working through the below actions, which were set out to ensure the beetles' protection.
These include:
- Removing invasive plant species such as riverside willow and Himalayan Balsam that grow on the banks of the River Ouse, helping to encourage the growth of Tansy plants.
- Planting clumps of the Tansy plant along the banks where there are large patches of space, as the beetles can only walk a maximum of 200 metres.
- Creating ark sites for the beetle; these are safe havens away from the river where their populations can be protected from summer floods.
- Working with landowners and land managers to reduce grazing pressure on Tansy plants by using short-term fencing and livestock management.
- Ensuring that during Ragwort control work, riverside land owners know the difference between Tansy and Ragwort plants.
- Yearly surveys by the group's volunteers to monitor existing populations along the River Ouse and in Woodwalton Fen.
- Increasing public awareness of the beetle, through BIAZA partner organisations.
- Captive breeding to facilitate research introductions and re-introductions.
- Re-introductions and expansion within the East Anglian Fens.
2023 proved to be a record year for the endangered Tansy beetle along the River Ouse. The annual survey, carried out by volunteers from the TBAG, revealed a population estimate of 91,000, which is nearly double the previous highest estimate of 46,000 back in 2016.
Our Aquarist Phill, one of the many volunteers in the TBAG, spotted 3,425 beetles along his transect in 2023, a huge increase from the 929 counted on his survey in 2022.
Conservationists have welcomed the positive news and say it demonstrates the success of changes to the riverbank’s management. Working together with local landowners, the group have helped ensure that the Tansy plant has been left to grow, allowing the beetles to complete their lifecycle.
Despite the record numbers, there are still concerns about how the Tansy beetle might cope with the increase in summer flooding events that are expected with climate change. The threat of the Tansy plant being out-competed by invasive plants, such as Himalayan Balsam, still remains.