Londoner Kris Gear was just hoping for a home run at a London Majors game when something whizzed passed his field of vision.

At first, he thought someone threw something at him.

"It was this moth and it landed on my leg. It looked like a massive spiker or something," said Gear, who said the moth sat on his leg for three or four minutes -- enough time for his seatmates to get a good look and for him to snap a few pictures and a video.

"It was scary looking, but it wasn't doing anything, just sitting there," Gear said.

It turns out the moth is a giant silk moth, or a Cecropia moth, which is about 15 cm wide and furry.

Even if it wanted to bite Gear, it couldn't -- the moth doesn't have a functional mouth.

Females emit a sex pheromone and males use their "big hairy antennae" to detect it, said Western University biology professor Jeremy McNeil.

The giant silk moth is one of the largest in North America. The one that landed on Gear was a male likely looking for a mate that got distracted by the bright lights of the baseball diamond where the Majors were playing.

"They don't get to spend much time alive. They emerge, find a mate, lay an egg, then drop dead," McNeil said.

"We don't see them because they only live for about a week or two. They aren't rare, we just don't usually see them in urban environments. We see them in deciduous forests."

They're nothing compared to moths in more tropical climates, where some silk moths hav a wing span double the size of the North American variety, McNeil said.

If you happen to come across a giant silk moth, it will only be in the next week or so. After that, they will have laid their eggs and died.

The caterpillars that eventually emerge from the eggs spin cocoons high in birch or maple trees, and they persist over the winter, McNeil said.

"They're just so beautiful," he said.

If you come across a giant moth, just relax and enjoy.

"Just let them be. They will eventually fly away," McNeil said.