These critters are a welcome addition to any garden. Not only are they important pollinators but they are also a pleasure to watch. Ask yourself if the caterpillar you saw had bristles or hairs, if it was smooth or bumpy. For butterflies and moths, have an idea of the size, colour and any body markings the butterfly or moth may have had.
If you would like help in identifying a particular caterpillar, butterfly or moth, check out the following references:
Peterson First Guides: Caterpillars by Amy Bartlett Wright
The Butterflies of Canada by Ross A. Layberry, Peter W. Hall, and J. Donald Lafontaine