“Is this a stink bug? Our house has a few of these, and they’re often walking on the walls. Why?”
This isn’t a stink bug, but that’s a very good guess!
This is a leaf-footed bug, a close relative of the stink bugs – they’re both members of Hemiptera, what entomologists call “the true bugs”. Beyond this, leaf-footed bugs and stink bugs both belong in Infraorder Pentatomorpha. While leaf-footed bugs do emit a strong smell when stressed or handled, but it’s not nearly as strong as a stink bug’s scent, in my experience.
These bugs are similar in behavior as well – they have piercing mouthparts, and tend to be herbivorous, especially seed-feeding. Both have been crop pests – stinkbugs are detrimental to agricultural pursuits like soy farming, while leaf-footed bugs tend to be more damaging in tree plantation contexts. In some regions, both may be present as minor citrus farming pests.
However, when the weather turns cold, both stink bugs and leaf-footed bugs seek shelter from the elements. In winter, both stink bugs and leaf-footed bugs build up protective alcohol-based compounds in their blood that make it much more difficult for them to freeze. However, if they do end up freezing, they die. Leaf-footed bugs are what entomologists would call “cold-tolerant, freeze-avoidant“. Their quest to find someplace warm to spend the winter sometimes leads them to bother us indoors. Without human homes to invade, leaf-footed bugs and stinkbugs both tend to overwinter inside large dead trees.
While they may be annoying for a time, rest assured that neither stink bugs nor leaf-footed bugs are harassing your houseplants this winter. During overwintering, these bugs avoid feeding – after all, the more moisture they take in, the more likely it is that ice crystals could form inside them. However, many leaf-footed bugs do release aggregation pheromones which spread the news that your home is a great warm place to wait out the winter.
As for why your new houseguests are walking on your walls, that I don’t have as good an answer for.
I imagine that your walls might be warmer than the floor, and that could make them more attractive. I’d also hazard a guess that your leaf-footed bugs prefer being on inside walls, rather than outside walls.
Thank you for the question!