Eurasian mealworms like to climb
In our first call about Eurasian mealworms, in 2015, the customer said these insects were falling from the ceiling. That was unusual for mealworms, and then, before we knew what species they were, and more about their biology (which is still not properly known), we assumed they had originated in the attic, breeding in a food source there. We could find no such source, and now know that these mealworms readily climb.
In this video, at 6:57, we document the Eurasian mealworms climbing fence posts. And here we provide some video showing how they have no problem climbing rocks.
It is clear now that the attic invasion calls (we have had more, since) are the result of the Eurasian mealworms climbing walls, all the way up into attics, and then down into the living areas of homes. This is indeed an unusual mealworm.