They are probably at their peak now and will disappear by the middle of July. We will not see them in Massachusetts again until 2025, although they will appear earlier in other parts of the country:
Their songs are different from the songs of ordinary cicades. The songs are more continuous and lower frequency, they can change the frequency by contorting their bodies -- each of them can sound a bit like a little alarm siren because of that. They are pretty fearless and can sing while sitting on a human hand or shirt.
Песни периодических цикад более непрырывны и более низкочастотны, чем песни обычных цикад. Часто они изменяют частоту звучания изгибом тела, поэтому каждая из них может звучать как маленькая низкочастотная сирена. Они вполне бесстрашны, и могут петь, даже сидя на руке или на одежде.
We saw them in various places on and to the right of Route 28 (we only explored the first few miles after the bridge to the Cape). They come in fairly large clusters and they are pretty loud, so one can hear them from a distance.
People are trying to keep track of those cicadas here: