Soil-binding pilosity and camouflage in ants of the tribes Basicerotini and Stegomyrmecini (Hymenoptera, Formicidae)

Workers of the tropical ant tribes Basicerotini and Stegomyrmecini possess two dominant forms of setae on the dorsal surfaces of the body and outer surfaces of the legs: longer "brush" hairs with splintered distal ends, and shorter "holding" hairs that vary among species from plumose to blade-shaped or filiform. The two usually but not invariably occur together to create a double layer. The brush hairs evidently scrape or otherwise capture fine particles of soil, while the holding hairs help to keep them in place next to the surface exoskeleton. As the worker ages, the soil accumulates as a thin, mud-like layer, greatly enhancing the overall camouflage of the body. The material appears to be primarily or entirely exogenous; no special secretory cells were found (in Basiceros manni, studied for this purpose) that might contribute cryptically colored chemicals or adhesive substances to hold the soil in place.