we bought a .5 acre lot through a home builder fully understanding that our lot backed up into a storm water detention basin.
The operative words in this statement are "fully understanding". It doesn't sound as if you were confused so not sure what you think you can do about the basin.
You obviously knew this before your house was constructed, so I think you're right. Nothing there. It's a small lot.
Nothing really wrong or illegal with wildlife and insects, so not sure what you might be thinking. What is the regrading supposed to accomplish and what easement are you referring to in this statement? Are you referring to the detention pond as easement? Traditionally an easement is a portion of your property set aside for utilities, etc. A detention pond, in my mind, is something totally different and you have no "interest" ownershipwise in it.
Have you contacted the water district or the county or whoever regualted detention ponds in your area? Make a run down to the county courthouse and snoop around the plat maps for your area. You might just find that the pond in question is all that was needed or you might find out that someone is cutting corners. Talk to the county engineer and see what they have to say.
I feel like we were mislead by the builder
Go back and reread your second sentence.
What rights do I have as a homeowner?
You have the right to question whether or not the developer(s) are following the guidelines on water detention ponds or the right to consult with a real estate attorney to try and stop the other developers from dumping more water into the existing pond.
"Never argue with stupid people, they will drag you down to their level and then beat you with experience." - Mark Twain