Answer: Has your moth orchid been outdoors, or in? If the former, I'd suspect snails or slugs. But this is only a guess. There is no common pest of moth orchids that produces the symptoms you describe, I'm guessing it is a general-type pest that feeds on many kinds of plants.
Examine the plant carefully. Pick up the leaves and look under them; scratch around the soil (or bark) that the plant is growing in. Something might be hiding right on or very near the plant. Look for the silvery "slime trails" that snails and slugs leave behind.
To reach the American orchid society, see:
For an article from National Gardening magazine about moth orchids, see:
Hope this helps.
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