Which of the following pests are commonly classified as occasional invaders?

Occasional invaders are pests that do not typically reside in a specific location but might enter homes or buildings under certain conditions, mainly when the weather changes, such as during colder months or when food sources become scarce. Stink bugs, ladybugs, and cluster flies are quintessential examples of occasional invaders.

Stink bugs, for instance, tend to seek shelter indoors as temperatures drop, looking for warmth and protection from the elements. Ladybugs also look for refuge in homes during colder months, particularly in late fall. Cluster flies are known to enter through small openings in search of a warm place to spend the winter. Their behavior typically aligns with the characteristics of occasional invaders, as they do not establish established populations indoors but rather infiltrate sporadically.

In contrast, the other options consist of pests that either are more permanent residents (like ants and termites in the first option) or are more commonly associated with structural damage and continuous habitation (as with rats, mice, and squirrels). Flies, wasps, and beetles can be nuisances but do not fit neatly into the occasional invader category due to their varied life cycles and behaviors in relation to human structures.