Both words mean "to caress" or "to fondle" according to the dictionaries. Is it really so? Are the exactly the same thing? If not, in what way does adding that "a" change the meaning? My question also pertains to several similar Spanish verbs that have a variant with the "a" prefix.
Some Spanish verbs are formed by adding the prefix a- and a verbal ending to nouns or adjectives. The a- prefix derived from the Latin prepositions ab ("agent") and ad ("source").
No precise rules on when to use the prefix, but usually is used when the verb formed means "to do something for..." or "the result of acting with..."
cabo = "end" ------> acabar = "finish, get to the end" licor = "alcoholic drink" = ----> alicorar = "get drunk"
But I insist it is not a general rule, in most cases the word is historically formed and the prefix has lost meaning.
plazo - aplazar compañía - acompañar tormenta - atormentar provecho - aprovechar pareja - aparejar manso - amansar largo - alargar seguro - asegurar cierto - acertar crédito - acreditar grato - agradar firme - afirmar consejo - aconsejar breve - abreviar premura - apremiar
In all these cases is wrong to omit the prefix (plazar, compañar, tormentar...)
The consciousness of etymology is lost in words like apagar, admirar, acostar, abrazar and adorar.
A similar situation occurs with the prefix en- (gancho - enganchar).
I don't thin that
cariciar exits as a verb. You have the name
caricia and the verb
I couldn't find
cariciar in the DRAE or RAE's Twiter and only this reference for cariciar online. I'm unsure up to which point the Wiktionary could be trusted more than the RAE. Maybe we have
cariciar due to regional differences; Maybe is just misspelled somewhere. It seems that cariciar is actually a verb in Portuguese. Maybe somebody made a mistake while editing the Wiktionary?
Hacer caricias. Tocar, rozar suavemente
Tratar a alguien con amor y ternura
Demostración cariñosa que consiste en rozar suavemente con la mano el cuerpo de una persona, de un animal
Regarding the second part of your question, in Spanish we have for example
Refregar o frotar fuertemente la piel con algo agudo o áspero, y por lo regular con las uñas.
I have heard people saying "arrascar" for this action although RAE doesn't contemplate it. I don't think that you can just add that "a" or take it for these verbs. Maybe there is an exception, but as a rule of thumb, I would avoid "arrascar", "cariciar", etc. Problably this is some sort of misunderstanding on the spoken language when you have an "a" in from of the verb.
Voy a acariciar al perro.
sounding like it was "Voy a cariciar al perro", and thinking that there is actually a "cariciar" verb.