I suspect -- but am not positive -- these are trichogramma wasp pupae on clover eating butterfly or moth caterpillar. The larvae emerged from the demolished caterpillar and pupated on the leaf.
If curious, I would put in a paper towel lined jar with rubber banded paper towel lid and see what comes out. (I am!

)
If they are wasps, then yes, they are beneficial (even if these might have eaten a nice butterfly caterpillar)
A fairly common butterfly to use clover as host plant would be a Sulfurs -- yellow butterflies... Have you seen any around? There's another one I'm thinking of bunt can't remember it.... Hmm I guess the other ones I'm thinking of must be Hairstreaks and Blues (tiny silver grey butterflies with tiny tails).