Alpheus heterochaeliswere collected near Beaufort, N.C. Males have a greater ratio of claw length/total body length than females. In field‐caught pairs, females tend to have longer bodies and males tend to have larger claws. In Y‐maze tests, males tend to seek females on the basis of chemical cues. The intensity of the sound produced by the large claw is positively correlated with claw size. Thus, stimulus intensity offers potential cues to the size of an opponent. Cine studies reveal that the large claw closes within 1.67–5.00 msec during snap production. An ensuing water jet travels at ca. 1.5–4.0 mm/sec and is directed toward an opponent. Size restrictions found in paired shrimp are hypothesized to result from an agonistic “balance”; established during initial contacts made prior to sex determination and pairing. The male's larger claw size/body size is explained by selection pressure favouring his mating with larger females who can produce more offspring.