Don't blame the trees, they're as unhappy about it as you are.
Every season brings different surges of insect populations. This year we are noticing an explosion in scale and aphid populations on our silver maple trees. If you haven't noticed the problem, just look at the line ups to the car washes around town! The tell tale sign of scales and aphids is the honeydew they excrete that drips from the trees on everything below, including shiny cars.
Scale insects are a funny group, they don't really move around much and they are not conspicuous. They feed on the tree by parking along the newer twigs, mostly on the undersides, and piercing their mouthparts into the tissues to extract sap. They filter out what they need and the rest is excreted as what we call "honeydew". This is a clear sticky substance that will adhere to any surface under the tree.
Ants have a unique relationship with honeydew producers; they feed on the sticky liquid. Ants will actually protect the scales and aphids from predatory insects like ladybug larvae. If you find a branch with aphids and ants on it, try poking the aphids with a little twig. The ants will attack the twig to protect the aphids. If you see armies of ants going up and down your tree, there are probably honeydew producers feeding on the tree.
Another sure sign of insects above are blackened surfaces under a tree and blackened branches within it. Sooty mould, a type of fungus, will colonize and spread on the honeydew leaving black splotches on fences, driveways, decks and patio furniture.
Control of these pests is difficult for unlicensed pesticide applicators and impossible on larger trees. On smaller trees you can brush off scale insects or hose off aphids with a hard jet of water. Understandably this gets progressively more difficult as the tree gets bigger.
Licensed arborists can perform trunk injection insecticide application to control the bugs. I caution that tree owners should only employ the use of pesticides if the tree's health is in jeopardy or if the enjoyment of their property is diminished. For example if your silver maple hangs over your deck, if the bugs are bad enough you can't enjoy that space without an umbrella.
Light insect infestations on your trees are nothing to be alarmed about. Most of the time trees can cope just fine with a portion of their energy sapped away by pests.