The Info page says some thrips are predaceous. Maybe they ate the moth eggs/embryos/larvae.

Do any of the specimens in the photos look like adults?

In large numbers they're probably a pest species. Do you notice any curling in the leaves? Areas that are darkened and not growing properly have thrips damage. Here's the UC IPM page on thrips, it has several pictures of beneficial species (Most of which are dark or brightly colored) and many pest species.

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7429.html

None of these look like adults yet, but there are a few with well developed wing pads that are close.

Thanks for that page. It describes two kinds that have yellow or yellowish larvae. However, it doesn't show photos of the larvae. I'll keep watching to search for adults where I last saw these yellow bugs.

Numerous blackberry leaves have grayish, dry areas, especially at basal portions where leaves overlap. That's the kind of space the bugs settled in after I returned their original leaf to where I'd found it. I had pruned it off and moved it for photos. I wired it back on, near its spot. A few hours later, it had dried somewhat, and the bugs were sheltered between two other leaves on the same stem.

If they suck plant juices and eat egg residue or caterpillars, they're not pure herbivores. The Davis page didn't describe any omnivores.

Adult thrips abound on the blackberry leaves. They're black and white, perhaps a different species from these larvae.

I've also seen just one larva that the Davis page indicates was Franklinothrips.

Predatory thrips do not occur in high numbers. I've gone through thousands and thousands of samples looking for pest and predator thrips in agricultural crops and we only find a few predators at a time but hundreds of pests in one small area.

Of course they're probably not really damaging your blackberries anyway, but just making more unsightly marks. Many many species of thrips have yellowish larvae, especially the pest species. They settle into the veiny areas because thats the easiest place to get juices. The gray dry areas are where the thrips are feeding and causing scarring. Predatory thrips would not be causing that damage, and if you had any other pests present I'm sure you would have noticed them by now.

Plus I'm pretty sure that one down in the lower part of the picture, and the one with the wingpads are feeding on the plant, and all that stippling and those black marks indicate they are feeding on your blackberries.