I have seen that before! However, I can't tell you what causes it, I only saw it a couple of times on a few plants. It caused no damage to the plants. I believe it actually comes from the plant rather than collecting on the plant. I thought it was odd how the water drops were only on the perimeter of the leaf. Hopefully someone knows what causes this.

I think it's dew too. The hairy stuff on the leaves must hold the drops.

Of course, none this morning at about the same time.

I almost touched and tasted it, but remembered that, last year I learned (the hard way) that my skin is really sensitive to the spines on the leaves and stems. It occured to me that if it was a secretion from the leaves that touching it might not be a great idea.

Squash plants are perfectly healthy (as you can see in the pics), first flowers are forming.