Have you ever fed your birds mealworms? They are the larvae of these beetles. There are almost 1,200 species in North America; most of them live in the desert but there are a few northeastern species that live in fungi, dead trees, or dry foodstuffs (like the oatmeal that the mealworms eat).
These relatively large beetles live on the ground or surfaces of logs. The adults are capable of burrowing into their substrate and they live side by side with their larvae.
Most adults have a chemical defense in the glands located in the abdomen. The chemical compounds of these secretions as well as the defensive behavior associated will vary but I haven’t been able to clarify if this variation is be species, genus, or individual.
Most Tenebrionids eat dead plant and animal matter. There are soil-dwelling ones that live on plant roots and seedlings and a few have evolved to specialize on fungi.