Historically, hot dog buns are available in eight-count packages. Spiders and octopuses also have eight limbs.
The number of hot dog buns in a pack is attributable to the fact that buns are usually baked in pans that can hold eight buns. The eight-bun pan is popular among bakers.
Spiders and octopuses also have eight limbs each. In the spider's case, all eight limbs are legs. In the case of the octopus, there are six arms and two legs, making eight limbs total. Spiders differentiate themselves from insects by having eight legs. In the case of insects, there are generally only six legs.