preferably a plurality of openings of different sizes are provided in the wall 2 at spaced intervals therealong and at least one of such openings must have the inventive configuration defined hereinbelow in terms of the vertical dimension thereof the stepping plate 5 of each opening 4 is preferably a flat surface inwardly and upwardly inclined toward the interior of the trap but at a smaller angle of inclination than the outer surface of wall 2 the roach collecting tray 1 can be molded by thermoforming into a unitary structure in the conventional manner the rough surface of stepping plate 5 can also be provided in the molding operation the outer wall 3 must be sufficiently low to enable a roach to traverse it and enter the trap through opening 4 in said inner wall cover 7 comprises a relatively flat panel having flaps 8 depending from the periphery thereof the flaps being engaged in and retained by the groove 6 between the inner and outer walls of the tray while fitting snugly against the inner wall the cover is provided with perforations 10 aligned with each opening 4 in the inner wall of the tray and which define the entrances into the trap if desired the perforations 10 can be located along only three sides of the generally rectangular section defining the openings but left unperforated along its fourth upper side.