You might be interested to learn that there is a significant population of aphids on the maple trees (especially the Norway maple) all around Burlington. There seems to be two species, a green one and a black one. Some are winged and some are not. This is a common occurrence at this time of year. Usually the aphid population builds and then the temperature warms up and the natural enemy population then comes along and brings the aphid populations down again. The natural enemies include lady beetles, hover flies (those cool flies that look like a honey bee, but tend to hover in one place over a flower); and parasites.
It is fascinating to watch the process. Just turn the leaf over and check it out. The lady beetle adults are easy to recognize, but the immatures are black with colored spots and sometimes spikes on their body. They look like tiny reptiles. You can tell that there are parasites around by looking for parasitized aphids. These look like an aphid with a hard shell on it. The parasite lays an egg in the aphid. The aphid dies and the parasite completes develoment within the body of the aphid. The parasite eventually cuts a hole in the abdomen of the mummified aphid to get out. You can see it with a hand lens.
These are sucking insects, and sometimes they cause distortion and cupping or crinkling of the leaves. They like new succulent growth the best. You can remove them by wiping them off, or rinsing them with a firm stream of water from a hose. Usually it is not necessary to treat an infestation because the natural enemies will take over. Aphids secrete honey dew, which drops on cars and you. Sometimes sooty mold, a blackish fungus, will grow on the honey dew.