The common name derives from its main foodplant, tansy (Tanacetum vulgare), but it can also use other wetland plants such as gypsywort (Lycopus europaeus) and water mint (Mentha aquatica).

It measures 7.7–10.5 mm in length and has a characteristic bright metallic green colouration, with pitted elytra and a coppery tinge.

[3] Other, small, fenland populations exist at Woodwalton Fen and at Welney Wildfowl and Wetlands Trust (WWT) reserve.

The tansy beetle was first described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae as Chrysomela graminis[4] and was later transferred to the genus Chrysolina.

Evidence from archaeological excavation has shown that its presence in western Europe is confirmed at least as early as the Neolithic period.

[21] The beetles may be found on tansy (Tanacetum vulgare) and water mint (Mentha aquatica) in fen land and the banks of rivers with broad floodplains in Britain.

[16] In Russia it may be found in the tundra zone from the Polar Urals to the Kolyma River, and in the nearby countries of Kazakhstan, and Mongolia.

[24] In the United Kingdom, its range is currently restricted to about 45 km of the banks of the River Ouse centred on York, North Yorkshire.

Tansy beetles had previously been recorded from Wicken Fen, Cambridgeshire, where species of mint (Mentha spp.

[22][25] In August 2014 a new sighting was made nearby at Woodwalton Fen,[26] following this a translocation programme of Yorkshire beetles was attempted to boost the population.

[22] Neglect may also lead to loss or degradation of habitat such as through over-shading or competition of food plants with invasive species such as Himalayan balsam (Impatiens glandulifera).

[31] The loss of habitat impacts upon the ability of the tansy beetle to find an alternative source of the host plant.

[34] Mated females lay batches of 3–15 elongated, yellow eggs (each 2 mm long) on the underside of the tansy leaves.

[25] In laboratory conditions, newly hatched larvae have been shown to survive for at least four days without food and thus have a long window of opportunity in which to reach a tansy plant.

[16] Long-term monitoring has indicated that survival during winter hibernation is surprisingly high, as autumn and spring population sizes are very similar.

[35] This is despite annual winter flooding of the River Ouse, implying that overwintering individuals must be extremely tolerant of long periods of inundation and oxygen deprivation.

[16] Both adult and larval tansy beetles are unable to detect their host plant, or each other, at a distance, either by smell, sight or a combination of the two.

The species has, however, also been recorded consuming a wider range of food plants including Lycopus europaeus (gipsywort), Stachys palustris (marsh woundwort), Achillea ptarmica (sneezewort), Mentha aquatica (water mint), Mentha rotundifolia (false apple mint), as well as other species of the genera Chrysanthemum, Scutellaria, and Artemisia.

For example, the steam distillate of fresh leaves and flowers of tansy contains high levels of camphor and umbellulone and is strongly repellent to the Colorado potato beetle (Leptinotarsa decemlineata).

[39] The species is formally designated as 'Nationally Rare' in the United Kingdom and categorised as a 'Species of Principal Importance' in accordance with the Natural Environment and Rural Communities Act 2006.

[22] In order to publicise the conservation project Rachael Maskell, the Member of Parliament for the constituency of York Central became a 'Tansy Beetle Species Champion' in 2016.

[47] In August 2024 a series of 17 metal tansy beetle sculptures were displayed in York and decorated by local artists to highlight historical 'trailblazers' in the city.