 Adult Lundy cabbage flea beetle measure around 3 millimetres ( 0 @.@ 12 in ) in length . They have brassy @-@ green heads and bodies , with reddish @-@ brown elytra . The adults feed upon the leaves of the Lundy cabbage , while the larvae mine into the plants to feed . The species is threatened by fluctuating numbers of Lundy cabbages , particularly due to invasive common rhododendrons ( Rhododendron ponticum ) . 
