Gap at shed ceiling and shed walls

by Linda
(Brooks Ky)

I have an Amish built wood shed, it's about 3 years old, It has double doors and 2 windows, I use it for outside cats, I have covered the windows with screen, and I had a screen door built so their would be air flow and the screen would keep bugs out, I have never had any trouble with flies until this year, it seems that they are on the ceiling, I was trying to see where they were getting in, and I noticed the very top where the boards come together and the sides where the walls attach to the roof, there are 1/4 inch gaps starting to form in places, Can these gaps be fixed with some sort of sealer, I never noticed them before, I can send pics if I need to, THANKS