It's instincts, it does not have brain capacity to think "ha ha ha a human! Let's be evil and ruin their picnic". Probably instead what happens is while crawli

It's instincts, it does not have brain capacity to think "ha ha ha a human! Let's be evil and ruin their picnic". Probably instead what happens is while crawling around it detects the surface it crawled on is actually the body of a large living entity, so going into defense mode is one possible response. Not sure if in this case it's because it may make you move to get free if stuck under you, or chase away possible threats to nest, or because possible food source?