Like many bees, the carpenter bee is a pollinator of many plants. When female carpenter bees bore into porch posts and barn beams, their intent is to build a nest, not to destroy our buildings.
To stop any structural damage that may result from their nest-building, you might try the following:
Dust diatomaceous earth into the nests.
Fill any holes with wood putty, then paint.
Can we say anything good about the pesky house fly? Yes! In recent years scientists have studied house flies to learn more about animal conservation. Of course, that doesn't mean we want house flies in our homes.
To control the house flies, try the following:
Screen your home.
Out-of-doors, introduce fly parasites. They are commercially available.