airlock activity (wild ale)

This is my first attempt at making a wild ale. Basically, I made 5 gallons of wort, left it exposed to air in my backyard overnight and put and lid and airlock on in the morning. Its been four days now and there is no airlock activity.
How long does does wild yeast from air exposure take to grow before you start seeing airlock activity?

 

This might not seem helpful, but it really depends on what yeast/bacteria(s) you may have captured. Airlock activity isn't a reliable fermentation barometer for 'standard' brewer's yeast beers, even less so for sour/brett fermentations and with wild caught yeasts all bets are off. When I did a wild yeast beer, I built up the yeast in a starter then pitched and it still fermented a little slower than a normal ale. Is your beer showing any fermentation signs, krausen?

 

it's my understanding that the number of yeast that you could have collected overnight were relatively few. essentially what occurred is that your wort is massively under-pitched. any bugs that you have in there are busy reproducing, but i'm wondering if you have enough in there to get a proper fermentation.

a more certain technique putting out a bowl of wort, verifying that you've got some fermentation, then stepping that up to a pitchable volume. wild beer breweries can used airborne yeast alone because they've perfected the process, the bugs live in the walls, etc.

 

Thanks for the replies guys. You are both right. I should have done a small volume starter to see if I am catching any yeast from the air.
Also, I have been researching on other brewing sites and many of them say that there maynot be airlock activity for weeks since the bugs maybe be slow fermenters.
Lesson learnt, I will do a starter from next time one!