In my lifelong absorption with butterflies and moths, I have never known anything as effective at catching them (temporarily) as the light trap which brought joy into my life thanks to Penny's secret birthday planning, five years ago. But there are other methods which also don't have the downside of my schoolboy net, which meant curtains (it was muslin, appropriately) for the insects.
You can track down caterpillars, for example, by checking their foodplants at the right time of the year. Nettles in late May and June are specially good for the Vanessids - Small Tortoiseshell, Red Admiral and Peacock - though remember that they sting. The nettles, not the caterpillars. It is also rare to pass a year without meeting a 'woolly bear', one of those hairy moth caterpillars which are intrepid pedestrians. They always seem to be going somewhere. Keeping caterpillars to pupation is a bit like having pets - constant feeding, familiarity with poo etc - but the reward of actually watching a butterfly or moth hatch is stupendous.
And now, this post's photograph. Pupa-hunting always struck me as a boy as the dreariest of pursuits. Romantic accounts of digging beneath appropriate trees didn't acknowledge the boredom and lack of rewards. But there are people who like fishing in canals, which seems to have about the same level of excitement. Serendipitous pupa-finding, however; that's another thing altogether. And here are two chrysalises, both vacated by their former occupants, which I just found while cleaning out flowerpots. One was an inch below the surface - imagine the force of instinct which gets a caterpillar to bury itself. The other was under the pot, tucked up inside the rim. I've displayed them on an extract from The Butterfly Collector's Vade Mecum which Miss Laetita Ford published in 1836. It's a great book.