White-lined sphinx caterpillars
Published in Yard and Garden News, July 1, 2007
Whitelined sphinx caterpillars were recently reported from two sites in central Minnesota (you can find this insect throughout Minnesota). In both cases they were feeding on evening primrose. They are also reported in the literature to feed on grape plants, plants in the Rosaceae (rose family), and many types of herbs and woody plants. They apparently feed June through July.
This insect grows as large as three inches long. You can identify it as a sphinx caterpillar by the distinctive horn or tail on the end of its body. The color of whitelined sphinx caterpillars is variable. Most are green with black stripes and yellow and orange markings, although some are mostly black with some greenish yellow. This insect turns into an attractive moth which can be seen visiting flowers at dusk in August and September. Because of its rapid wingbeats and darting motions it is often mistaken for a hummingbird.
In most cases, you can ignore whitelined sphinx caterpillars in your garden. If they are causing more damage than you wish to tolerate, try to move them to an alternative food source (you will have to experiment to see what they like). If that is too much effort, than just handpick them and throw them into a bucket of soapy water. You should not need insecticides to deal with these caterpillars.