1. Expression of weapons and weapon sizes are remarkably affected by environmental factors in armed insects, resulting in remarkable morphological difference in larger and smaller males i.e., male dimorphism

2. The phenotypic plasticity is one example of alternative mating phenotypes. Selection on the alternative phenotype generates different suites of multiple traits between larger and smaller males such as morphology, behaviors and life history. The different subsets of traits can contribute to reproductive success of larger and smaller males, respectively.

3. In order to understand how alternative phenotypes evolve, studies that couple differences in life history and reproductive traits between larger and smaller males are required. Here we investigated differences in morphology, behaviors, and life history in Gnatocerus cornutus.

4. Larger males have relatively larger mandibles and the advantage in male fighting to access females. Also, the developmental period was significantly shorter in the larger males than in the smaller males.

5. Smaller males with rudimentary weapons have higher locomotion ability. This suggests higher performance in the dispersal to new territories. Larger and smaller males showed different suites of multiple traits, and the combinations of multiple traits are probably related to expression of weapons.