One would have thought that Tansy Beetles (Chrysolina graminis) from their name just eat the tansy plant (Tanacetum vulgare). However, the adult beetles are known to vary their location, if not always their diet, by laying eggs on neighbouring plants including nettles and anything nearby to prevent predation by other Tansy Beetles.
In 2013, in an attempt to observe what happened, we planted some water mint (Mentha aquatica) and apple mint (Mentha suaveolens) near to some existing tansy patches. We’re now planning to add gipsywort (Lycopus europaeus) to the collection and observe what becomes of that.
In September 2014 the mint plants still had beetles munching away on them, whilst they had largely disappeared from the many tansy plants. We are informed that captive beetles don’t successfully breed when on a diet of mint, which is of concern when we learn of the recent discovery of Tansy Beetles at Wood Walton Fen, and the reintroduction at Wicken Fen where there is no tansy, but time will tell in both York and Cambridgeshire.
Just to be confusing the Tansy Leaf Beetle also has a relative – the Mint Leaf Beetle (Chrysolina menthastri) of a bluer hue than the greener tansy one.