I'd witnessed a similar phenomenon a couple of years back while reading on the balcony one sunny morning. A continuous stream of butterflies proved increasingly distracting, many of them drawn to the brightness of the open page. As with the Vagrant Emperors, unusually good breeding conditions in Africa had triggered a boom in the Painted Lady population, and they were heading north.

Other, less transient, wildlife can be found on a balcony, especially one with unswept corners and neglected plant pots. Jumping spiders can be observed waving their palps about and ambushing prey. Geckos scuttle up walls, and will make a dash for the interior of your flat through an open window. Their voracious diet for insects makes them useful house guests. Once I saw a bizarre Thread-waisted Wasp enjoying a quiet groom on the railing, providing an opportunity for closer examination. Its thorax and abdomen seemed on the point of separating, joined together by the thinnest waist imaginable.

And in the winter, there are many birds in town, looking for food in the warmer urban climate. If you refrain from spraying with pesticides, Chiffchaffs will come to pick the bugs off your plants, their small sharp bills able to handle tiny insects.

Lucy Brzoska runs nature tours and writes for www.iberianature.com.