Wespen stechen manchmal, wenn sie sich bedroht fühlen.

German often leaves out the article when talking about things in general.

• Wespen = wasps in a general sense
• Die Wespen would more likely mean the wasps — a specific group already known from context

So:

• Wespen stechen manchmal = Wasps sometimes sting
• Die Wespen stechen manchmal = The wasps sometimes sting / Those wasps sometimes sting

Yes, stechen has a broad meaning that includes to prick, stab, sting. When talking about insects like wasps, bees, or mosquitoes, stechen is the normal verb for to sting or to bite depending on the insect.

So in this sentence:

• Wespen stechen = wasps sting

Even if English uses a special verb like sting, German often uses stechen.

Manchmal means sometimes.

In the sentence:

• Wespen stechen manchmal = Wasps sometimes sting

Its position is very natural in German. Adverbs like manchmal are flexible, but they often appear in the middle part of the sentence.

You could also hear:

• Manchmal stechen Wespen, wenn sie sich bedroht fühlen.

That changes the emphasis a little, but the meaning stays basically the same.

Because wenn introduces a subordinate clause, and in German subordinate clauses are separated by a comma.

So:

• Wespen stechen manchmal, wenn ...
• ..., wenn sie sich bedroht fühlen.

This is standard German punctuation.

Here wenn means something like when or whenever.

The idea is:

• Wasps sting sometimes when they feel threatened
• or more naturally: Wasps sometimes sting if/when they feel threatened

In German, wenn is often used for:

• repeated situations: when/whenever
• conditions: if

So here it carries both ideas a little: whenever that situation happens, this is a possible result.

Because the part after wenn is a subordinate clause, and in German subordinate clauses usually send the conjugated verb to the end.

Compare:

• Main clause: Sie fühlen sich bedroht.
• Subordinate clause: ..., wenn sie sich bedroht fühlen.

That final verb position is one of the most important features of German word order.

Because the verb is sich fühlen = to feel.

German often uses fühlen reflexively when talking about how someone feels:

• Ich fühle mich müde. = I feel tired.
• Sie fühlen sich bedroht. = They feel threatened.

The reflexive pronoun changes with the subject:

• ich → mich
• du → dich
• er/sie/es → sich
• wir → uns
• ihr → euch
• sie/Sie → sich

So sich is required here.

Bedroht means threatened.

It comes from the verb bedrohen = to threaten.

So:

• sich bedroht fühlen = to feel threatened

This is a very common expression in German.

Because the subject is sie, referring to Wespen, which is plural.

German verb endings depend on the subject:

• ich fühle
• du fühlst
• er/sie/es fühlt
• wir fühlen
• ihr fühlt
• sie fühlen

Since Wespen = they, the correct form is fühlen.

Sie here refers to Wespen.

So:

• Wespen stechen manchmal, wenn sie sich bedroht fühlen.
• Wasps sometimes sting when they feel threatened.

Because Wespen is plural, sie means they.

No. Here sich belongs to fühlen, not to stechen.

The structure is:

• sie fühlen sich bedroht = they feel threatened

It does not mean:

• they threaten themselves
• or they sting themselves/each other

The reflexive pronoun is only part of the expression sich bedroht fühlen.

Because German often uses this pattern with sich fühlen:

• sich + adjective/participle + fühlen

Examples:

• Ich fühle mich krank. = I feel sick.
• Er fühlt sich sicher. = He feels safe.
• Sie fühlen sich bedroht. = They feel threatened.

So bedroht works like a description of their state.

Yes. German uses the present tense for general truths, habits, and typical behavior, just like English often does.

So:

• Wespen stechen manchmal = Wasps sometimes sting

This does not mean they are stinging right now. It means this is something that happens in general.

Then the main clause must still keep the verb in second position, so the subject moves after the verb.

For example:

• Wenn sie sich bedroht fühlen, stechen Wespen manchmal.

Notice:

• subordinate clause first: Wenn sie sich bedroht fühlen
• then main clause: stechen Wespen manchmal

This is a classic German word-order pattern: subordinate clause + verb first in the main clause, then subject

Manchmal is the most direct and natural choice here.

Other options exist, but they are a little different:

• oft = often
• gelegentlich = occasionally
• ab und zu = now and then

So manchmal fits very well for a neutral sometimes.