It was the most unusual art opening of the South Florida season. The gallery was a back wall of the Miami Children’s Museum. The artiste was clad not in a tuxedo but a white plasticized jumpsuit and cloth mask that made him look like a cleanup worker at a biochemical spill or maybe just Woody Allen dressed like a sperm in Everything You Always Wanted To Know About Sex.

And the work was not a painting or a sculpture but a 35-square-foot mosaic of a character from the old Space Invaders game, mounted about 20 feet up the side of the wall, where its reflective-tile eyes seemed to follow the motorists speeding along the MacArthur Causeway with a kind of ominous cheerfulness.

Of course, no opening is complete until the critics have spoken. The most influential, in this case, would be the bosses at the Children’s Museum, who had no idea their wall was host to a giant outer-space parasite. The artist had mounted it with a nuclear-holocaust-proof epoxy glue at 3 in the morning, using a niche in the wall to conceal himself from a security camera about a hundred feet away.

“I’m interested to see how the museum will react,” said the artist, beaming up at his latest creation. “For me it’s a gift I gave to the museum. Some people would pay to have a piece like this in their house. But at the same time, it’s totally illegal.”

South Florida, meet the French street artist known only as Invader. (“But you can call me Space!”) His clandestine mosaics of characters from Space Invaders, Ms. Pac-Man and other 1970s video game characters have been popping up over the past 15 years on walls, freeway abutments and bridge pillars everywhere from Paris to Katmandu. And about two weeks ago, they began appearing around Miami-Dade.

He has put up more than 25 so far, ranging from a cute little six-by-four-inch creature at the bottom of the small wall in front of an apartment building at 15th and Collins to a eight-by-nine-foot blue behemoth with hellish red eyes mounted on the wall of a utility building on Northeast Second Avenue near the intersection with Second Street. There’s even an Invader mosaic on a blocked-up window on the south wall of the Gusman Center on Southeast First Street. (There are also a couple of dozen pieces around town from an earlier Invader visit that went unnoticed during the hubbub of the 2010 Art Basel festival.)

Reaction has varied. When the staff at the Children’s Museum finally discovered the creature on their back wall on Friday, they delightedly posted a photo on their Facebook page captioned “Look what we found on our building!” and asking if they should keep it. Unanimous verdict of readers: yes.

But when an employee at Jerry’s Famous Deli on Collins was asked if anybody had found a mosaic that Invader installed inside the restaurant on Wednesday, he replied warily: “I heard something about that...You’d better talk to the general manager.” Who, alas, was not available.

Confusion and caution are not unusual when it comes to Invader’s work, says Carlo McCormick, a New York curator and critic who’s an enthusiastic Invader fan.

“Is it real art, or just a goof or vandalism? All of the above, hopefully,” McCormick said by telephone Friday. “That’s art for me — serious, but also goofy and a little bit vandalistic. What I wonder about is why people who question whether Invader’s street mosaics are really art don’t also ask what 16-year-old girls are doing in skimpy little bras in underwear ads, or the increasing privatization of public space that’s taken over by advertising...