Can bugs fly up between floorboards?

We would like to put a screened-in porch on top of our deck. We wish to keep the floor as is, with spaces between the planks. We were told that we should have no problems with mosquitoes and blackflies as they will not travel up through the gaps. Is this true?—Ilana Emerson, Bracebridge, Ont.

Well, there’s no law of physics that says these bloodsuckers can’t fly up. “They can and they will and they’re really good at it,” says Bob Anderson, an entomologist at the Canadian Museum of Nature in Ottawa. That said, a bug may zero in on you through the screen, but it’s not likely to realize that it must go down under the floor and then up through the spaces to reach you. It’s a mosquito, not Lassie. “I don’t think that’s a strategy they’d figure out,” says Anderson.

To be safe, you could block off the gaps between the floorboards by installing the same type of screening on the underside of the deck that you use up top, suggests Doug Currie, the entomology curator at the Royal Ontario Museum. That way, “you wouldn’t get anything coming up.”

We’re assuming this deck is low, not a second-storey balcony. If there’s a lot of space underneath, hungry bloodsuckers would already be there, flying around, so their route to reach you would be more obvious. Cocktail hour is ruined!