1. In Spanish and Portuguese, adjectives change their endings to match the gender and number of the nouns that they qualify (Spanish: un caballo blanco, dos caballos blancos, una casa blanca, dos casas blancas; Portuguese: um cavalo branco, dois cavalos brancos, uma casa branca, duas casas brancas). But adjectives do NOT change their endings in English: a white horse, two white horses, a white house, two white houses.
2. In Spanish and Portuguese, the plural of nouns and of adjectives is made by adding the letter 's' (sometimes 'es').
3. When Spanish and Portuguese adopted the Latin word larva, they adapted the plural by adding the letter 's' to the singular, just as in other Spanish and Portuguese words. [French, German, and Italian also adopted Latin words and changed them into French, German, and Italian by changing the endings of the plural form and in some languages (French and German) the singular form too].
4. Most nouns in English form the plural by adding the letter 's' just as in Spanish and Portuguese. There are exceptions (goose/geese, mouse/mice, ox/oxen, woman/women, etc.). There are more exceptions in a few words of French origin that have been adopted into English (e.g., eau/eaux, bureau/bureaux [British English keeps the French plural bureaux, but American English has changed it to bureaus].
5. However, English has adopted many Greek and Latin words, especially in the biological sciences, and most of these words keep their original Greek and Latin plurals.
6. Only English among the major western languages has not changed
the Latin endings:
7. Larva is the singular in English (and Latin and Spanish and Portuguese and Italian). Larvae is the plural (in English and Latin, but not Spanish or Portuguese or Italian). There is no such thing as "a larvae" -- so please do not use this expression even if you hear it from people around you, because they are wrong.
8. Portuguese and Spanish have simplified their grammar from the original Latin (from which both were derived). Nouns and adjectives now have only two genders (masculine and feminine), not three (masculine, feminine, and neuter). Nouns no longer have six cases -- their endings change only according to number (and in a few instances gender): the genitive (= possessive) case does not exist in hispanic languages. But in German, and even English!, the genitive case still exists. In English we can write "cat's eye" -- forming the possessive case by adding "'s" to the noun -- but in Portuguese/ Spanish we have to write "olho de gato"/ "ojo de gato", which is more cumbersome because there is no possessive case. "Mary's book" has to be written in Spanish as "el libro de María" -- and thus a translation from English to Spanish (or Portuguese) usually takes more letters, words, and space.
9. The definite article is often not used in English in places where in Spanish and Portuguese it would be used. English usage requires "Dr. Smith is..." (not "The Dr. Smith is"), "Entomology is..." (not "The Entomology is...").