What is this tiny bug that has infested my deck?

We've had the deck for 3 years and never saw anything like this. Millions of tiny silver/green bugs crawling all over the wood and fake wood deck. Some are the size of a head of a pin, others are a bit larger but not the size of a grain of rice. They are the shape of a sesame seed. There are large patches of what looks like dead ones that have turned white. Help! We can't sit outside!