Learn Hardcore Russian: Моя мама боится и беспокоится, когда я задерживаюсь вечером. - My mother is afraid and worries when I stay out late in the evening.

Although both express negative emotions, боится emphasizes fear or being scared (e.g. of something bad happening), while беспокоится highlights anxiety or unease. Using both adds nuance: your mom is both afraid and uneasy when you’re late.

Why is the verb задерживаюсь in the imperfective (present) rather than the perfective?

The imperfective задерживаюсь describes an ongoing or habitual action—“I stay late” or “I’m late repeatedly.” If you used the perfective задержусь, it would mean a single, completed event: “I will end up staying late (once).” Here we talk about a recurring evening situation.

What case is вечером, and why is it used here instead of something like в вечер or по вечерам?

вечером is an adverbial form derived from the instrumental case.

It answers “when?” and means “in the evening” (generally that evening).
в вечер is ungrammatical (would need a full noun phrase like в тот вечер “that evening”).
по вечерам means “in the evenings” (habitually, plural), which slightly shifts the nuance from “on evenings when I stay late” to “every evening.”

Why is it “моя мама” and not just “мама”?

In Russian you can say мама alone (she’s assumed to be your mom), but adding моя (my)

clarifies possession,
emphasizes your personal relationship.
It’s common in spoken and written Russian for speakers to use possessives even with close family terms.

What’s the difference between беспокоиться and волноваться, which also means “to worry”?

беспокоиться often implies a sustained state of concern or fussing over something.
волноваться leans toward an emotional reaction—“to get worked up,” “to be excited/nervous.”
They overlap, but беспокоится is more about steady worry, while волноваться can be momentary excitement or anxiety.

Can I change the word order, for example putting вечером at the beginning?

Yes. Russian is flexible:

Вечером моя мама боится и беспокоится, когда я задерживаюсь.
Моя мама вечером боится и беспокоится…
Shifting вечером to the front adds slight emphasis on “in the evening,” but the core meaning remains unchanged.

Why is there a когда-clause with present tense? Doesn’t “when I stay late” sound odd in English?

In Russian, you can use когда + present tense to describe general or repeated situations:

“When I stay late, my mom worries.”
In English you’d naturally say “whenever I stay late,” but Russian uses когда for both “when” and “whenever” in these habitual contexts.

Why do these verbs all end in -ся (боится, беспокоится, задерживаюсь)?

The -ся suffix makes them reflexive or middle-voice verbs:

беспокоиться literally “to do worry to oneself,”
бояться is inherently reflexive (“to fear oneself”),
задерживаться means “to be held up oneself.”
Many Russian verbs that describe states, emotions or certain actions use -ся to indicate the action happens to the subject.