Do investors/traders actually take the summer off? July and August. Every year 2 months vacation. Volume and volatility is usually low in the summer.
Absolutely some of them take the summer off. Don't believe me look at the daily volume. A trader I respect a lot, Tim Morge, mentioned the line to leave the CME was much larger than normal about 2 week ago. That doesn't mean you can't make money.
Taking 3 months of Summer vacation is mostly a "European thing" though there may be some New Yorkers and Chicagoans who do the same. They'll be back after Labor Day.