Perhaps to confuse a predator, some tropical beetles are colored by optical interference that is due to scales whose alignment forms a diffraction grating (which scatters light instead of transmitting it). When the incident light rays are perpendicular to the grating, the angle between the first-order maxima (on opposite sides of the zeroth-order maximum) is 26 degrees in light with a wavelength of 550 nm. What is the grating spacing of the beetle?