If the deer are going to the trees they probably are eating some. Crab apples are fairly small and go down in 1 piece compared to a Delicious where it may take a few bites. Are the apples still hanging on the tree? I find that that the deer usually eat the ones that have fallen first, then the low hanging apples. Is there shelter for the deer to get to the trees without being seen?

Try putting some other apples under the trees to see if the deer eat those. Don't handle the apples but squish a few by stepping on them to get the aroma in the air. You could also try putting some corn in the same spot. If the deer don't eat the corn and larger apples you've got something scaring them off or they have easier pickings elsewhere.

Dan O.