Atomic resolution scanning tunnelling microscopy (STM) has been used to study in-situ the As-terminated reconstructions formed on CaAs(001) surfaces in the presence of an As-4 flux. The reconstructions c(4 x 4), (2 x 4) and (3 x 1) are long established for GaAs(001) between 400 and 600 degrees C for varying Ga and As flux, however the stoichiometry of incommensurate transient reconstructions is still uncertain. By performing high temperature STM on an initial (2 x 4) surface between 250 and 450 degrees C in the absence of an As flux, small domains with varying reconstruction are observed in a similar manner to the InAs/GaAs(001) wetting layer. The local storage of excess Ga in Ga-rich domains could provide insight into sub ML homo- and hetero-epitaxial growth. (C) 2009 Elsevier B.V. All rights reserved.