Two of these were taken in pitfall beneath fresh carrion bait. The elytra appear to have raised bumpy ridges between striations in some photos, but not in others. I'm tempted to think the elytral hairs simply held the water in this fashion after I rinsed the beetles for their photo shoot, and it made the surface appear lumpy until they dried out.

Why would dung beetles come to carrion? Well, a freshly dead animal is likely to contain a quantity of dung that could be harvested.