Examen ad apiastrum venit.

The subject is examen.

You can tell because:

• venit is a singular verb, so it needs a singular subject.
• ad apiastrum is a prepositional phrase, so it cannot be the subject.
• examen is the remaining noun and fits as the nominative singular subject.

A useful extra point: examen is a neuter noun, and neuter nominative and accusative forms are often identical. So the form by itself can look ambiguous, but the sentence structure makes its role clear here.

Because examen is a collective noun. It refers to many creatures as one group, just like English swarm.

So Latin treats examen as grammatically singular, and the verb is singular too:

• examen venit = the swarm comes / the swarm came

Even though many individuals are involved, the grammar focuses on the group as one unit.

Because it follows the preposition ad, and ad takes the accusative.

Here ad shows movement toward or to something, so the destination is put in the accusative:

• ad apiastrum = to/toward the apiastrum

Also, apiastrum is a second-declension neuter noun, and its accusative singular ends in -um, which looks the same as its nominative singular.

Ad means to, toward, or up to, depending on context.

In this sentence, it marks the goal or destination of the motion. With venit, it tells you where the subject is coming:

• venit ad apiastrum = comes to / came to the apiastrum

So ad is doing an important job: it shows that the motion is directed toward something.

Because Latin word order is much more flexible than English word order.

English usually depends heavily on order:

• The swarm comes to the plant

Latin depends much more on endings to show grammatical function, so the verb is often placed at the end in a neutral or common style:

• Examen ad apiastrum venit

That does not mean the verb must always be last. Latin could also say:

• Ad apiastrum examen venit
• Venit examen ad apiastrum

Those versions are still understandable, though they may shift emphasis slightly.

It can be either one, if macrons are not written.

Without macrons, venit is ambiguous in spelling:

• venit = comes (present)
• vēnit = came (perfect)

In many Latin texts, macrons are omitted, so you rely on context or on the translation you have been given. If your lesson gives the meaning as present, read it as comes. If it gives a past meaning, read it as came.

Because Latin has no articles.

English distinguishes:

• a swarm
• the swarm

Latin usually just says examen, and context tells you whether it is definite or indefinite.

So in this sentence, examen could mean a swarm or the swarm, and apiastrum could likewise be understood from context.

Examen is a third-declension neuter noun.

Its dictionary form would be something like:

• examen, examinis

That is why it does not have the more familiar first- or second-declension endings like -a or -us.

This is worth noticing because English-speaking beginners often expect Latin subjects to look like -us or -a nouns, but many common Latin nouns belong to other declensions.

No. Apiastrum is not the direct object here.

Instead, it is the object of the preposition ad. The whole phrase ad apiastrum tells you the direction or destination of the motion.

So the structure is:

• examen = subject
• venit = verb
• ad apiastrum = prepositional phrase showing movement toward something

That is an important distinction, because accusative case in Latin is not only for direct objects. It is also used after many prepositions, including ad.