Learn Portuguese (Portugal): É de lamentar qualquer erro ao identificar uma espécie letal. - Any mistake when identifying a lethal species is to be regretted.

The structure ser de + infinitive (like é de lamentar) is used to give an evaluation or express that something deserves to be or ought to be done. While é lamentado states a pure fact meaning 'it is regretted', é de lamentar carries a judgment, meaning 'it is regrettable' or 'it is to be regretted'.

Why does the subject qualquer erro come after the verb phrase É de lamentar?

In Portuguese, it is very common to invert the subject and verb in evaluative statements. You can perfectly well say Qualquer erro é de lamentar, but placing the strong judgment É de lamentar at the beginning of the sentence puts the emphasis on the evaluation rather than the mistake itself.

Why use ao identificar for 'when identifying' instead of translating 'when' as quando?

Using the preposition a combined with the definite article o and an infinitive verb (like ao identificar) is a very natural Portuguese construction meaning 'upon identifying' or 'while identifying'. You could say quando se identifica, but ao identificar is much more concise and elegantly links the action to the mistake.

How does the meaning change if I put qualquer after the noun, like um erro qualquer?