They seem to be heaviest in June, but they can be found in April depending on the weather. If you're trying to attract them, plant a datura. They love them, but all parts of the plant are toxic to us.

Hah - attract them NOT. I want to know when to cover my tomato plants. What is the weather pattern that brings them in earlier? Thanks andy.

I believe early heat and humidity will bring them out earlier. Last year I saw a few at the start of May and it was in the 90s in my back yard in February.

One trick to keeping them off your tomatoes is to plant something they like much more, like Datura. I did that one year that we had them especially bad and they completely stripped my Datura down to it's lower branches and left everything else alone in my yard. The datura was back to normal like nothing had happened to it within a few months. The downside to Datura is the seed pods, they are just another thing to clean up.

That's a good idea, a sacrifice plant but I've had datura before and keeping ahead of the seed pods can be a real trick. I'll just cover with mosquito netting. Thanks for the input Andy.