The millipede Brachycybe lecontii Wood, 1864 is a social millipede known for forming pinwheel-shaped groups and for paternal care of eggs. Brachycybe lecontii is endemic to the eastern U.S., and its distribution overlaps with another species within the genus, Brachycybe petasata, from the Southern Appalachian Mountains. Molecular data, however, show that the closest relative of B. lecontii is Brachycybe nodulosa from East Asia. Here, I investigated various aspects of the life history, paternal care, defense, feeding, and social behavior of B. lecontii, and provided morphological and anatomical descriptions using light and scanning electron microscopy. Based on detailed observations of millipedes from 14 localities in the distribution of B. lecontii, I found the following natural history aspects. The oviposition period of B. lecontii was from mid-April to late June and the incubation period lasted 3–4 weeks. Males exclusively cared for eggs, but care of juveniles was not observed. In one case, the clutches of two males became combined and they were later cared for by only one of the males. The defensive compound of B. lecontii consisted of two isomers of the alkaloid deoxybuzonamine. Defense glands were large, occupying up to a third of the paranotal volume, and were present on all but the first four body rings. Stadia I juveniles do not have defensive secretions and stadia II juveniles have defensive pores but do not secrete. Secretions were observed only in stadia III millipedes and older. I observed Brachycybe lecontii feeding on liquids from fungi of the order Polyporales, and describe a cuticular structure on the tip of the labrum that may relate to fungivory. I found that pinwheel-shaped aggregations do not form in the absence of fungus and suggested the aggregation is associated with feeding. I describe and illustrate a previously undescribed comb-like structure on the tibia and tarsi of the six foremost leg-pairs and measure and analyze the spectral reflectance of B. lecontii exoskeleton. / Master of Science in Life Sciences / Millipedes are important members of the ecosystem as decomposers. By eating dead vegetation such as wood, leaves and other detritus, millipedes fragment the material thereby allowing further breakdown by fungi, bacteria, and other microbes. Microbial decomposition further reduces the detritus into its chemical constituents (e.g., carbon, nitrogen, and simple sugars) thereby releasing these materials into the ecosystem for future generations of life to use. In addition to the millipedes’ critical role in the ecosystem as decomposers, they are fascinating and yet understudied. For example, millipedes of the species Brachycybe lecontii are pink, have males that exclusively care for the young (a rarity amongst arthropods), form star-shaped aggregations of individuals, and emit a novel alkaloid-based chemical secretion. By understanding the natural history of this local Appalachian species, I provided a fundamental basis for future studies of its sociality, chemical defense, and evolution.