They both have a small lip (less than 1cm) with a yellow border around it. How can a non expert identify them? Identification of those two species is not easy but not impossible either.
One must pay attention mostly to the bending of the lip. The lip of Oprhys parvula is almost straight across the longitudinal axis, starting to bend (if at all) just after the 2/3rds of its length whereas the lip of Ophrys cinereophila is bending downwards right from the start, at the basal area.
In general, Ophrys parvula is a sorter plant with fewer flowers than Ophrys cinereophila and usually it is found among phrygana, whereas Ophrys cinereophila can be found in a greater variety of habitats like woods, dry meadows and phrygana.
Of course those two species, as the majority of orchids of the genus ophrys, have a different pollinator. Andrena tomora for O. parvula and Andrena cinereophila for O. cinereophila.
Ophrys parvula was considered endemic to the southern part of Rhodes island but recently Zissis Antonopoulos found similar plants in central Cos and Giannis Gavalas in Iraklia (Small Cyclades). It seems that this species is endemic to Southern Aegean islands.
Ophrys cinereophila is distributed from SW Greece to Dodecanese, Cyclades, Crete, S Anatolia and Lebanon.