Maybe they are looking for prey insects that aren't actually there.

Or are.

Thanks for the reply... no insects visible. I've harvested 3 heads so far (cut to 1", bottom leaves still intact, and regenerating very nicely!) - I wash each and every leaf before eating, and they are all pristine. But you think the wasps just THINK there should be insects to munch? And oddly, they don't mess with the romaine or oak leaf red plants... at all!

Hmmmmm.... curious

RainyPNW

Here is a link that might be useful: My 2010 Garden Blog - please check it out!

The leaves of that cultivar might just be good platforms for resting and warming up. Or there is a sweetness that draws them, watch what they do closely and you may see something that is telling.

Are they drinking/ carrying water?
Does that type of lettuce have a wrinkled surface that holds water?

Wasps would have two reasons to be around lettuce. One reason is water (for mud/paper nest building), but wasps would normally gather water/mud from the ground, not the plants.

The second reason is that many wasps eat caterpillars; If your leaves have any holes in them, caterpillars are around. Wasps can "smell" damaged/chewed leaves from a great distance and it is possible the watering makes tiny fractures in the delicate lettuce leaves. The wasps would be fooled into checking it out.

Wasps spend the entire summer bobbing up and down at our vinyl roof gutters. They do this by the hour, to no apparent benefit. So your lettuce-leaf wasps may be barking up the wrong tree also.

Thats funny ; i googled this subject and it brought me here .
I , too . have a simpson lettuce that the red wasps love .They are no bother , and I do have something eating holes
in my leaves of my other lettuce plants , i just havent figured out what is eating them .Im sure theres something in the lettuce that keeps them happy .

Could be aphid eating wasps. You don't see the aphids because the wasps are doing their job.

I agree they could be going after the water. Paper wasps will make many juants a day to our pool or bird bath for water and scrape our deck for the pulp. They're paper wasps. Last year almost all of them disappeared for some reason. We've had many nests on the house for years and never had wormy broccoli. I don't use insecticides or herbicides, so I have no idea what happened to them. There aren't any this year either. Any one else missing them? The only big change was a cell tower going in, but it was in before they vanished. I'd really like to have them back.

Lettuce bees, lettuce bees, ooooooohh lettuce bees! There will be an answer... Lettuce bees.

Googling why wasps love my lettuce. They are very kind to it so I leave them beeeeeeeee