The red amiral butterfly distributes its eggs one by one on its hostplants, the stinging nettle. The caterpillar is relatively easy to find.
One week after spotting the adult around the hostplant, you look for rolled up leaves, if the leave is closed their is a caterpillar inside.
Raise your caterpillars in a rearing box or in a cage by supplying them fresh cut hostplant in small water viles like they use at the florist.