Good visitors to your home look after it with care. They leave you olive bread for when you get home after a longish flight, they keep the place clean and eat everything you leave there for them (and nothing that isn't theirs.) They also eat all the nasties lying around the place and look pretty while doing it.
Bad visitors do this - they mangle the furniture beyond repair and eat it along the way. Who woulda thought just one bunch of bad aphids could do so much damage to a forming plant.
Previously I have mentioned my torment with a horde of snails. Good visitors or bad visitors - I know which ones I prefer! In balcony gardening in particular, with the confined space, wierd microclimate and close proximity of plants it seems pests run really rife. I know Mum's broccoli was similarly covered in aphids, in her vast garden, though the icy weather seemed to finish those off for her, and what brassica doesn't get mauled from time to time. But thus was a cornflower, none of which have been overly attacked in the garden before. It was so infested that it grew wildly, wrongly and finally wilted and died. I would have pulled it earlier but I left it as a form of science experiment (and maybe secretly hoped it would act as a beacon to lure ladybugs.)
How do you manage pests? Sprays, picking them off and throwing them away (like caterpillars and snails) or encourage natural predators like ladybugs. I know I employ all three, in a balcony garden the battle is constant and with the lack of nearby gardens most good pests seem to steer clear.