What is this insect?
This insect turned up inside our school building in the science lab. it reminds us of a Dobsonfly, but it is 3 1/2 cm long. We didn't have a stream running thru our classroom last time we looked, so we are puzzled by the appearance of this little critter.
District of Columbia County District of Columbia
It looks like you've found a giant stonefly (Pteronarcys sp). https://www.marylandbiodiversity.com/viewSpecies.php?species=10284
You are correct that these are typically associated with water, but sometimes they can be found away from streams and rivers. They are attracted to lights at night. This article has more information about them.