Size. With so many different species, there are snakes of many different sizes. The world's smallest snake, according to National Geographic, is the thread snake, which grows to only about 3.9 inches (10 centimeters) long.It looks much like an earthworm.The largest snake, the reticulated python, can grow to a whopping 30 feet (9 meters).ize. With so many different species, there are snakes of many different sizes. The world's smallest snake, according to National Geographic, is the thread snake, which grows to only about 3.9 inches (10 centimeters) long.