Larvae of Callosobruchus maculatus (F.) can coexist in a bean and exhibit scramble-type competition although the larvae can kill each other. Mechanisms to prevent or neutralize interference should be necessary for scramble-type competition. Previous studies reported that C. maculatus larvae can make walls to fill in their intersections after they encounter each other in a bean. To examine whether the wall-making is related to a mechanism behind scramble-type competition of C. maculatus, we examined larval wall-making behavior in a geographically isolated strain, in which the larvae exhibit scramble-type competition but retain interference ability. We conducted longitudinal dissection of beans with two hatched eggs to examine the pattern of wall-formation against larval development and the relationship between wall-making behavior and larval coexistence in a bean. The frequency of two individuals separated by the wall structure increased with developmental day, and eventually became higher than that of cases without encounter on the eighteenth day after oviposition. This indicates that the wall-making behavior may be associated with the coexistence of larvae in a bean. We also conducted an artificial interference experiment with pairs of larvae taken from beans with walls to examine whether larvae need to make walls for avoiding interference interaction. The pairs showed lethal fighting after the walls had been removed. This indicates that larvae made walls to avoid interfering with each other in a bean. These results support that wall-making behavior is a mechanism behind scramble-type competition in C. maculatus.