Where do you live?  I'm guessing it's in the SW part of lower MI?  Nearly all of lower Michigan has experienced a major gypsy moth outbreak. Much of the NE and NW had high GM densities beginning in 2019 or 2020, but the outbreak collapsed in most areas in 2022 or 2023. Outbreaks generally last about 3 years - maybe 4 - before pathogens, especially a virus (NPV) build up in the population and cause a big die-off.  During outbreaks, oaks and often other hardwood trees can be completely defoliated. Those trees are adapted to dealing with defoliation. They will produce new buds around mid July and be OK (unless they have other serious problems).  Conifer trees like pines, spruce, etc cannot produce a second set of buds.  If those trees are being defoliated, you need to spray them with a registered insecticide (Sevin, malathion, etc). Most of the caterpillars are probably feeding on the oaks right around your house, I'm guessing.  THere will be a few more weeks of this - caterpillars get bigger, eat more leaves = more defoliation and more frass (the science word for insect poop).  

By about July 4th, the caterpillars will finish feeding, spin a cocoon and pupate, then moths will come out.  Dont worry about the moths - they dont feed and they only live a few days.  The females lay one egg mass each and thats it.  You just gotta get thru the next few weeks.  

It's is getting pretty late for using Bt sprays.  Bt is the best option - it only affects caterpillars and only if they eat sprayed leaves.  It works best on young caterpillars tho.  You can check with a certified arborist to see if they have high pressure spray equipment that can get the insecticide spray up into the canopy of the oaks.  Don't worry about spraying trees in the woods - just protect the trees right around your home.  

You can try a DIY option called AceCaps.  This is a general use insecticide (acephate) (available on Amazon) that is packaged in capsules similar to a big vitamin pill.  You drill thru the bark on the oak, just into the sapwood, then shove a capsule into the drill hole.  Dont drill too deep - the outer few rings of sapwood are carrying all the water, plus this insecticide. Then you move over and up a bit and do it again.  YOu have to follow the label directions - number of capsules depends on the diameter of the tree at 4.5 ft aboveground.  It doesnt work for EAB in ash trees but it should be at least somewhat effective on gypsy moth caterpillars.  Put a piece of duct tape over the drill holes or fill them in with silicon so that the little beetles that vector oak wilt can't get into the holes.  This is the high risk period for oak wilt. Unlike gypsy moth, oak wilt will kill the oaks.  

Finally, google "MSU gypsy moth" and you will get to a website that has lots of information.  There are 2-3 page writeups about options for dealing with GM around your house, defoliation impacts, Bt, the diseases that cause GM outbreaks to collapse, etc.  Would be good to get educated - hate to say it, but chances are, you'll be dealing with GM again next summer.  Be sure you know what the egg masses look like - anything you can reach, scrape into soapy water and let it soak for a 2-3 days.  This will pass - just a few more weeks.

Deb