Preheat the oven to 375 degrees F (190 degrees C).
Unroll crescent dough. Pinch or press the perforation between the triangles to get four rectangular pieces. Cut rectangles in half lengthwise, making eight narrow strips.
Make a 2-inch slice through the center of one end of a hot dog. Cut two more 2-inch slices on either side of that slice, so the "legs" are about the same thickness. Repeat on other end. Cut "legs" into remaining hot dogs.
Roll a crescent strip around center of each dog. Place spider dogs on an ungreased baking sheet.
Bake in the preheated oven until golden brown, about 11 minutes. Dip a chopstick into some ketchup and dot "eyes" onto each spider. Serve with remaining ketchup.