These are Euonymus Leaf Notcher caterpillars, and we've received multiple questions about them from Maryland residents this year, so they must be having a banner year for some reason. The type of Euonymus pictured appears to be Burning Bush, which is invasive and a species we encourage gardeners to replace if possible. In either case, the caterpillars are almost done feeding this time of year and will soon be wandering off to form a cocoon. Plants recover well enough on their own to not need treatment, but options for insecticide use (which should only be a last resort) are included on the linked page for this pest.

Miri

Burning bush and other invasive species can spread (often through wildlife like birds eating the berries/seeds) into natural areas, crowding-out native vegetation and wildflowers that some of our native insects and other wildlife depend on. Nearly every county in Maryland has documented Burning Bush growing wild, usually in woodlands or on the edge of woods. Even though seedlings of Burning Bush don't always appear in the same garden or landscape where they are planted (though they can), they can easily spread into nearby woods. Because of these negative impacts, we recommend that gardeners don't plant species that behave invasively in Maryland, and remove and replace those that are already growing with other species. True, this won't fix the problem already present with hundreds of other Burning Bush already in wild areas, but it may help to prevent the problem from worsening.

Miri