croc expression is first detected at the anterior end of the early embryo (stage 5). The expression then fades from the anterior-most point corresponding to the prospective stomodeum. Expression then fades further and is connected by a thin line of cells behind the stomodeum in a germ band extending embryo but is still present in the labrum. Expression at the germband extended stage is found along the back of the stomodeum extending laterally into the procephalon and has retracted from the labrum.

croc transcripts are expressed predominantly in embryos and are also detected in larvae and adults. They are first detected in embryos at the anterior and posterior regions. The anterior expression appears as a ventrally shifted anterior cap while the ventral expression consists of a transient ventrally located posterior spot. During the cellular blastoderm, the anterior cap retreats from the pole region to form a tilted stripe that covers the anlagen of the stomodeal invagination up to the position of the clypeolabral anlage. During gastrulation, the cap retreats and transcripts accumulate in the developing foregut and in the intercalary segment anlage. In the posterior region, expression is reinitiated in an area corresponding to the developing mesoderm adjacent to the hindgut. During the extended germ band stage, croc-expressing cells form a cell cluster associated with the developing foregut that eventually lines the posterior pharynx wall. In addition, croc-expressing cells occur in metameric pattern in the developing mesoderm.

croc transcripts are expressed in two spatially restricted domains in blastoderm embryos which correspond to precursor cells of anterior and posterior gut derivatives. During gastrulation, they appear in a subset of cells in the CNS.