A farmer mowed his field , it was a dry day and cow dung and dust was flying everywhere . The wind picked it up , a cold front approached and it rained on your car . A manure spreader was fertilizing a large field , it was a dry day and dung was flying everywhere, the dust was picked up by prevailing winds . A storm front approached washing the dung from the skies landing critters on your car. Tree worms were hatching as they usually do in summer and rains washed them from the leaves and branches onto your car. http://www.allaboutworms.com/worms-in-trees