This species of fly belongs to the R. suavis group, which has a natural history consistent with allopatric speciation.

R. juglandis was first described by E. T. Cresson, Jr. in 1920 from material from the exocarp of fruit of Juglans regia (the English or Persian walnut tree) in Arizona.

[2] Upon developing into larvae, these flies take on a transparent look in their early stages and turn creamy white or light yellow as they mature.

The female fly is larger than the male, and has a more pointed end of its abdomen due to the telescoping ovipositor.

[2] In addition, R. juglandis has been found to infest the Arizona walnut Juglans major in the southwestern United States and Mexico.

The female searches for a suitable spot for oviposition; when one is found, she forces her ovipositor several millimeters into the husk of the walnut.

The spot of oviposition darkens after one or two days; then, the egg cavity can be detected with the naked eye.

The larvae hatch from eggs after 4 to 7 days and immediately tunnel into the inner portion of the husk of the walnut.

After maturation, as completion of development usually occurs after the infested walnut falls off the tree to the ground, the larvae exit the decaying husk and go onto the soil, in which they burrow and transform into the prepupal stage within 8 to 24 hours.

[11] Threats to the larvae in shallow depths include predators like ants and parasites like wasps from the genus Coptera.

[8] Adult flies feed on dew and plant sap and can also dissolve solid deposits on foliage for nutrients using saliva.

Male flies demonstrate low-frequency wing vibration, accompanied by airborne infrasound.

Males then respond based on encounter rates with females at different levels of ripeness.

Experimentally, females were shown to land more on green models than yellow or brown ones, and experienced males followed the same patterns.

[13] In addition, researchers have found that flies seem to internalize changes in sex ratio in the surrounding environment and respond accordingly.

R. juglandis females drag their ovipositors on the husk of the walnut after oviposition, which suggests that they have released a marking pheromone, a behavior typical of the Rhagoletis genus.

However, the flies reinfest the same walnuts, and even the same oviposition sites, created by individuals of the same species.

[15] In large, less-infested walnut fruits, adult fly size has been found to be larger and larval survival is higher.