The egg period, egg size, and daily changes in egg size were investigated in the field cricket, Teleogryllus emma. T. emma inhabits the slope of the Oishi Dam (OD) (38.03°N, 139.57°E) and Arakawa riverside (AR) (38.09°N, 139.57°E) in Sekikawa Village, Niigata Prefecture, Japan. We studied OD, AR, and the F1 hybrids, viz, OdAr (OD females × AR males), and ArOd (AR females × OD males) and determined whether daily changes in egg size are related to shortening of the egg period of T. emma on the dam slope. The egg periods in OD, AR, OdAr, and ArOd were shorter at higher temperatures (p ≤ 0.05). Furthermore, the egg period in OD was shorter than that in AR and OdAr (p ≤ 0.05). After oviposition, the eggs enlarged due to water absorption and entered diapause at the embryonic stage of the array. The major axes of eggs in OD, AR, OdAr, and ArOd expanded daily and were influenced by temperature whereby a higher temperature resulted in an increase in the major axes. At 15ºC, the major axis gradually increased after oviposition, reaching its maximum at 130 days. The eggs grew rapidly at temperatures ≥ 20ºC and reached their maximum size at 10−14 days, 5−7 days, and 4−6 days after oviposition at 20, 25, and 30ºC, respectively. The expansion of the major axis up to 7 days after oviposition showed that the egg size in AR increased faster than that in OD at 15ºC, while that in OD increased faster than AR at 20, 25, and 30ºC, indicating that the expansion rate in OD and AR eggs differed with temperatures. Temperature-dependent changes in the expansion rates in OD and AR up to 7 days after oviposition suggest that they may be associated with shortened egg period.