Slice sausages in half lengthwise, then cut each half into two pieces.
Using the tip of a knife, make three 3–4 cm incisions at both ends of each sausage piece, leaving the center intact.
On a work surface, unroll the crescent dough. With your fingers, press the perforations to seal and form a rectangle. Cut into 24 strips, about 2 cm wide and 5 cm long.
Wrap one strip of dough around the center of each sausage piece and pinch to seal.
Place on a parchment-lined baking sheet, seam side down. Decorate each with two olive slices for eyes.
Bake for 10–12 minutes, until the dough is golden and the sausage “legs” are crispy and curled.
In a bowl, pour the ketchup and use mustard to draw a spiderweb on top. Serve with the sausage spiders.
