Simple - It's not there. The "Ark" was probably a small boat or raft that some guy rescued two goats off a gravel bar during high water event, but it got better and better in the retelling over 2,000 years before Moses wrote the story down. In myth all things are possible. Please explain where all that water would have come from or gone to afterwards? Or even that two of every animal was able to swim, crawl or trot to the middle-east from places like Australia and the Americas. A flood would have been no issue after that.
The Ark wouldn't have been able to hold just the insects if you took two of each of the 700,000 or so known species. ;-)