Tent caterpillars are the pupal stage of the Gypsy moth. During this phase of growth, the caterpillars spin webs that look like tents. These tents protect the caterpillars from weather and many predators.
The caterpillars will devour all vegetation in and around their tents. If there are enough of them or if the bush or shrub they are on is weak or young than they can easily stress it enough for it to die.
Tent caterpillars like trees in the Rose family. That includes fruiting trees such as peach, plum, apple, cherry and crabapple as well as hawthorn.
In early spring take a look around trees that tend to have tent caterpillars. Look for the eggs which are laid in clumps around small branches. The clump will look like a black jelly Bean.
If you don't find the eggs and the caterpillars appear, remove the tense manually and crush the caterpillars. I have used a high power hose to remove the tents but the caterpillars remaining will just spin new ones if you don't get rid of them
If you spray pesticides, the tents will often protect the caterpillars. It's best to remove them manually.
Birds love them so if you have a lot of birds in your area then you will have assistance from them.