Sentence:  A male that sees another male ahead of him going up the hill speeds up to overtake him, "just in case" a female actually is there. Hence the apparent <WSD>tag teams</WSD>! Many insects, including both diurnal and nocturnal moths, use airborne sex-attractant chemicals (pheromones) to facilitate mate location. 
Meaning of the word marked with <WSD> tags:  A gangbang.