I've found through macro photography of mushrooms that many times what you perceive as a clean prime specimen of a mushroom may actually have already been heavily infected with bugs. The damage may not be apparent at first, but upon close scrutiny you will see tiny bugs and tiny holes in the mushroom which the bugs produce. You may even notice tiny deposits left by the bugs (eggs or...). Also, the oysters that I find in the spring and summer usually always have bug infestation. That's why I much prefer the fall / winter oyster mushrooms. Based on what I saw last year during an early chanterelle season, the bugs were ravenous for the first mushroom fruiting of the year on which to feast and lay eggs. In many years, oysters may become their primary initial target.