Thank you Jonathan and Martin for your quick replies! We are on the second
floor, so not too high, and we overlook a large garden with lots of fruits
trees - in fact a massive pear tree stretches right up and beyond the height
of our balcony so close we can almost reach out and pick the fruit.
Hence we seem to get plenty of insects, mainly wasps as they come for the
pear tree, but also bees, butterflies, ladybirds, hover flies. I will try
the paint brush trick though this afternoon - thanks for the tip both of
you - and I will also try and get a cutting or another plant.

Tracey