Filling gap between threshold and step outside

[donmaico]

Hello,
I have a gap running along the width of the door which is about 15mm in height and was wondering what i can use to to fill or whether i should leave well alone .I have thought about using filler foam but I am inclined to think the gap is there for a reason.
The reason I ask is because we get ants coming into the house and the seem to be nesting under the patio somewhere near the bifold door entrance.There is also a gap in the side off the step where it meets the wall Anyone got any suggestions? Thanks

 

[Johnny Allround]

Hi Don, can you post a photo of the area of concern, thanks?

 

[noseall]

Hello,
I have a gap running along the width of the door which is about 15mm in height

There should be no gaps. It's what foam was invented for. Just make sure the doors are shut and locked before foaming.

 

[donmaico]

on closer inspection I noticed there was some foam at each end of the step but not much in the middle .The other photos shows one side of the step with a crack along the mortar which could look ants through

 

[donmaico]

I read in a comment on another thread that bifold doors are notorious for re adjusting themselves over a period of time which I way I was hesitant about applying foam