Sonnet-Who Am I?

I am a linear, legless, Vertebrate; Bellying the earth, ever since my birth; Of varying sizes, colours, shapes; I mate, And swallow whole, life many times my girth. I writhe and snake my way up fast; I am the 'Sentinel of Land and sea'; Most people look at me awe-struck, aghast; I hiss and scurry forth frightened, may be. My fangs are poison-filled and also not; I scour the earth, listening to vibrations; Most people hit my head with sticks when caught, I'm King of Night's earth-holes of all nations. But I'm a Snake! Oh, just a rubber-Snake! For Heaven's sake, the beating all I take.