Something eating into rind of oranges

Hello all, I have a Valencia orange tree that is doing quite well, except that today I noticed that something has been eating into the rinds of the developing oranges, quite a few of them. I was wondering if anyone has ever seen this and what mite be doing it, I don't see anything on the tree except maybe a few spiders.

 

Probably snails & slugs. They can can do some real damage to citrus leaves & fruit.