The germinating seeds of plants called dodder must find a host within a few days or they will die. The nettle is a favourite target and the dodder seedlings can tell if one is feeble or well-nourished. As the dodder grows around the nettle it inserts tubes into the stem and sucks out the sap, fuelling its own growth and its hunt for another victim. A relative of bindweed, the dodder climbs in a similar way, its tendrils always searching and winding around other plants. Once it's fully established and sucking the sap from hundreds of nettles, it can finally flower, producing bundles of little white blossoms. Eventually the whole nettle bed is overwhelmed by hundreds of writhing dodder stems.