I use Terro liquid ant bait. It's liquid borax. Ants eat it and take it to their nest and they're gone. Actually fun to watch them.

I also use terro, takes a week or two.

Uh, I see, are you both referring to the below product? And if so, wouldn't that be too messy along the flat-top of my backsplash (compared to the Stick-On-Chalk idea i had in my original post? Especially since the goo might run over behind the backsplash?

Remember i mentioned the big gap behind it, built by the 1950s amateurs.
My above-mentioned link did contain glowing chalk testimonials (not just terro ones).

http://s7d2.scene7.com/is/image/woodstream/us-t100t200-in-use-1

The terro I use, comes in a small flat, clear plastic container. If you are concerned, Place the container on a piece of parchment paper.

I did not not click on your link. Terro in my area is available in many different applicators.

Terro takes time.

Is there a reason you do not want to use an insecticide (spray chemicals). I have found insecticides very effective and immediate. But, treating the ant entry point is important.

Re your structural problems, I do not have enough info to comment.

Sprays are ineffective when it comes to invading nuisance ants.

Commercial baits are far better because the ants share it with family in the nest.

As has been said, will take time. Perhaps days to weeks.

Cool counters.

My homemade recipe which you see on the red counter is purported to be like Terro. I'm gonna try the combo of swabbing Dawn plus spraying vinegar behind backsplash at next invasion. I saw that on Wiki, among other things.

Basically, i'd been wondering whether it would have helped to

• stick double-sided scotchtape along flat-top of backsplash
• then stick paper, cardboard or other onto the scotchtape
• then color the aforesaid with chalk...

(per my o.p. and because chalk helped various people per that link)

Instead of a homemade, Terro like recipe, I recommend using Terro. I have not tried the other things, and have not needed them.

I see thank you all for your input. Which of you clean your counters & sinks with vinegar prior to placing the terro traps?

Actually, the reason for my OP, is that years ago i'd bought a type you squeeze from a tube, which i'd squeezed onto the metal-edging atop backsplash (all along it). And it seemed to be very effective.

After years of using various remedies for tiny light brown ants in my kitchen I read somewhere to wipe the counters of orange oil. I did. They disappeared and never came back. I'm still amazed that it was as easy as that. I had used several brands of ant bait trays. Some they would eat and some they did not. Not sure if Terro was among them.

Interesting thanks! I'll keep it in mind. Meantime, the handyman came and hopefully sealed the gaps as per the attached pics.

(you can see from the angled-cut of the wood, how off-kilter houses were built back in the 50s! Which is why he needed to angle the wood wider at one end & narrower at other end)

Note i've seen ants anyway (both the sugar & black) even after it was done. Whether i'll suffer swarms of sugar-ants like before, i guess time will tell.

P.S. I still don't know what the black ant pictured in my above photo is called. I hope it's not a carpenter ant!