The pattern of gnawing is quite inconsistent from plant to plant to be a the work of one culprit. Caterpillars (night dwelling) and perhaps cockroaches are both a possibility.
You could try to spray eucalyptus oil. I have no idea if that will hurt the orchids.
I hope you eradicate the critters as soon as possible.
Good luck.
chefatplay: I love Dracula and vampires and I am yet to find a vampire that can live on plant sap.
If they did Bram Stoker would have had a bit of a problem
