The theme song for this year's box office is shaping up to be "Holding Out for a Hero." Superhero movies have been just about the only safe bet in 2017, providing a reliable box office boost during a hit-or-miss year. Hollywood has hauled in about $6 billion at the U.S. box office through July 9, roughly even with the total at this point last year, according to comScore. That's thanks to strong early releases like comic book movies "Logan" and "The LEGO Batman Movie," as well as the live action "Beauty and the Beast," low-budget horror breakout "Get Out" and "The Fate of the Furious." But things have taken a turn for the worse since the start of the summer movie season, and it's only superhero flicks — "Guardians of the Galaxy Vol. 2," "Wonder Woman" and "Spider-Man: Homecoming" — that have been sure bets.

Box office receipts are down 7.7 percent between May and July 9, marking a second summer slump. Last year, the total was down 1.2 percent from 2015 — a record year at the box office. "We're down — but versus a summer of 2016 that was not exactly impressive in terms of the number of sequels that failed," said Paul Dergarabedian, senior media analyst at comScore. "Last summer was the summer of sequelitis." That sickness appears to have infected this year's theaters to some degree. The list of sequels that have disappointed includes "Pirates of the Caribbean: Dead Men Tell No Tales," "Transformers: The Last Knight," and "Alien: Covenant." Meanwhile, four of the top six movies this year are based on comic books — and the early success of "Spider-Man: Homecoming" is sure to make that five of the top seven. The summer has only posted two positive weekend-to-weekend comparisons with last season, and both of them correlate with comic book movies: the debut for "Wonder Woman" and the second weekend "Guardians of the Galaxy: Vol. 2" screened. The year started out lagging behind last year, but the cumulative domestic box office total rocketed ahead of 2016's year-to-date total with the March release of "Beauty and the Beast."

That surplus shrank with the release of "Guardians of the Galaxy Vol. 2." Though it is the second top grossing movie of 2017, it faced a tough comparison with the same week last year, which saw "Captain America: Civil War" debut. The surplus spiked higher with the hugely successful release of "Wonder Woman" in June, which went head to head with last year's disappointing Teenage Mutant Ninja Turtles sequel. But then 2017 once again fell behind last year's running total. The premiere of "Spider-Man: Homecoming" last weekend helped to eat into that deficit, and Dergerabedian said the opening weekend of "War for the Planet of the Apes" this weekend could help pull 2017's box office haul even with last year's. To be sure, some of this year's domestic under-performers look like winners on the global stage. While the fifth "Pirates of the Caribbean" movie ranks at number 9 in the United States, it sits at number 5 around the world. "The Mummy" jumps from number 19 at home to number 11 globally.