By ‘life sized’, do you mean ‘on the scale of elephants’ and other animals which are larger than us (more maximum scariness)? Yes, I suppose that if, say, a microscopic creature such as a midge, or a flea were the size of an elephant, then I would have thought that they might make life a little inconvenient for us!
It reminds me of the film ‘Starship Troopers’ – but I can’t say it was an amazing film, and it is super gory. But anyway, the aliens in that were like gigantic insects, and they ate humans like it was going out of fashion.
If microscopic creatures were suddenly made really big then they might be able to eat humans or something. It wouldn’t really happen though, because they wouldn’t have all the structures inside them that they would need to be big – like a blood circulation system or a complicated digestive system.
They also wouldn’t be able to do the same kind of damage to humans as some microscopic things, like bacteria and viruses, do now because they wouldn’t be small enough to get inside our bodies and travel to cells and damage cells.