Caterpillar problem on Dendrobium and Epidendrum

[sparverius]

A few weeks ago we noticed large amounts of insect droppings among the roots of a mounted Epidendrum stamfordianum. Careful cleaning with forceps produced four smallish caterpillars, under 1 cm long, that keyed out to the genus Polites, aka grass skipper butterflies. Yesterday we found them in the mount of a Dendrobium jenkensii as well. I am loathe to use chemicals and have been able to control them (so far) with manual methods. I am concerned about possible root damage caused by the probing, however. I have checked all the print and online resources I can find and none of them address caterpillars feeding on epiphytic orchids. Has anybody else encountered this problem and, if so, what did you do to control them? My butterfly larva reference says Polites feed on grasses in the wild so I guess I shouldn't be too surprised that at least a couple of them have switched to orchids

Dave C