This is a Spotted Lanternfly nymph, and we are receiving several reports of their activity in the greater Baltimore region so far this year. (This is expected, as the insects occur nearly state-wide at this point, and you are closer to the original epicenter of activity when the pest is new compared to most other counties.) No action is needed (we do not recommend any insecticide use), but if you want, you can report the sighting to the MDA, as mentioned on the page linked above.

Miri

thanks Miri!