A balcony is no ecosystem.
That a balcony is no ecosystem is, of course, not a novel insight. Yet sometimes one needs a little reminder. Over the past couple of days, this caterpillar and its twin have devoured more melissa leaves than I would need for a cup of tea. And since the city birds of our street are spoiled by fast food and pizza, they did not seem to care about a fresh green dose of proteins.
Because of its love for herbs, I think it is the larva of a Silver Y. But this is more of a guess.