Nice find! Giant Leopard Moths are quite common in Maryland, and have been documented across the entire state. We would not consider them rare, though perhaps many people don't encounter them. The BugGuide database states that "larvae feed on a great variety of broad-leaved plants, including banana, cabbage, cherry, dandelion, maple, orange, sunflower, violet, willow." Their diet is so wide-reaching that, if you wanted to try planting hosts to support them, you might need to just include a variety of native species, since they are far from being host-specific. (Granted, some of that quoted plant list is non-native, but native plants would be ideal so they can support other wildlife as well.)

Miri