With these data, I evaluated the effects of parental photoperiod and offspring environment on prolonged egg diapause, embryonic development and hatching over nine years in natural settings populated by Mormon crickets in the Bighorn Mountains of Wyoming.On July 9, 2015, Mormon crickets were collected on Paint Rock Road (44° 27' 48.853" N, 107° 27' 38.279" W, 2654 m) in the Bighorn Mountains as 7th instar nymphs and reared in the laboratory at 15:9h light:dark, warming to 30°C during the day and cooling to 24°C at night. Adult females were paired with adult males and each pair was housed in a nylon mesh cage (30x21x21 cm) with a 20x20 cm aluminum pan filled with clean, dry sand for egg laying. Mating pairs were split between two photoperiod treatments: 19 pairs were designated long day (LD) adults and placed in an environmental chamber with a 15:9h light:dark cycle; 20 pairs were designated short day (SD) adults and placed in a second environmental chamber with 12:12h light:dark. Eggs from 12 SD pairs were sifted from the sand on September 3 and the same number of eggs from each pair (n=2, 2, 3, 7, 7, 7, 7, 7, 9, 9, 11, and 14 eggs) was buried approximately 2 cm beneath the surface in seven sand-filled 10 cm, plastic plant pots (height 8.9 cm, volume 500 ml) for a total of 85 eggs per pot. The pots had a 7.3 cm diameter, plastic mesh net covering the drainage hole at the bottom and a 20 cm diameter Lumite net (1.5 mm mesh, SI Corporation, Gainesville, Georgia) covering the 10 cm diameter, open top, fastened by cable ties around the waist of the pot to prevent small animals from entering and hatched nymphs from escaping. Similarly, eggs from 14 LD pairs were sifted from the sand on September 3 and split evenly between seven sand-filled plastic pots (number of eggs from each pair per pot: n=1, 1, 1, 1, 3, 3, 3, 4, 7, 7, 8, 11, 11, and 13 eggs) for a total of 74 eggs per pot. A temperature datalogger (Maxim 1922L thermochron) was buried 2 cm beneath the surface in each LD egg pot. One SD and one LD pot were set side by side in the ground on September 9 or September 10 at seven locations (Table 1) in the Bighorn Mountains, Wyoming with the top of each pot even with the ground surface and covered by a galvanized steel hardware cloth (6 mm mesh, 18 x 18 cm) stapled at four corners into the ground to prevent large animals from disturbing the pot of eggs.In late August or early September of each year that followed (2016-2024), the pots were collected, the sand from each pot was dumped into an aluminum cake pan, and air dried overnight. The eggs were examined with the aid of a dissecting scope and categorized into hatched, failed hatch (nymph opened but did not exit egg shell), fully developed (with the eyespot at the end of the egg), half-developed (with the eyespot halfway along the egg), undeveloped (no eyespot visible), dark and flat, fungus, broken, and missing. In four instances, a parasitoid exit hole was also noted. Temperature data loggers were downloaded annually and replaced as needed. In 2016 to 2018, all of the eggs except those that had hatched, failed hatch, or broken were reburied in the pot. From 2019 onwards, eggs that were hatched, failed hatch, broken, or dark, flat, and appearing inviable were discarded (eggs with fungus were returned to the pots). Pots were returned to the same locations where they were collected on the day the eggs were reviewed or the following day.