Keratinophagy and the horn moth's curious protuberances

This Cape buffalo (Syncerus caffer) skull was found in Kruger National Park, South Africa. The distinctive projections on its horns are tubes made of silk and frass (excrement) created by larvae of the horn moth Ceratophaga vastella (family Tineidae).

An adult moth oviposits on the horn, perhaps placing its eggs in small cracks or holes on the horn's outer surface. Upon hatching, a larva begins to consume the horn, incorporating its frass into an enveloping tube. Eventually, the larva will pupate inside the tube, from which it will later emerge as an adult. Tubes with closed ends are occupied by individual larvae or pupae, while tubes with open ends are unoccupied. The exuviae (casts) of previously emerged moths might be seen protruding from a subset of the open-ended tubes.

Keratinophagy, the consumption of keratin as a substantial portion of the diet, is rare (New Zeal J Zool 2002; doi.org/10.1080/03014223.2002.9518285). Ceratophaga are the only tineids that feed exclusively on keratin. The tubes may protect subadults from predators and the physical environment. It would be interesting to learn how the larvae—inside their respective tubes—maintain their water balance, and what role the tubes play in that process. Because keratin is nitrogen-rich, horn consumption and processing by larvae could have important implications for nitrogen cycling and soil microbe communities at local scales.

These tubes have been documented on the horns of other bovids, such as the kob antelope (Kobus kob). Nevertheless, the output from an online image search suggests that there is a strong preference for horns of the Cape buffalo. If there is indeed such a predilection, might it be due to the relative thickness of the buffalo's horn sheath? Both the number of tubes per horn and the length of individual tubes vary, though the reasons for such differences are not understood. Relatedly, we have not found evidence of these larvae feeding on the keratin in hooves. Many questions arise in trying to understand these moths and their curious tubes.