Spitzer/IRAC 8 µm emission map (in a flux range of 0–98 MJy/sr) of a part of the Cygnus-X complex (Beerer et al. 2010). The yellow rectangle outlines DR18, which is studied here. The white circle has a radius 12.2 pc (at a distance of 1.4 kpc), with its center at the position of the trapezium (Cyg OB2 #8, RA 20^h33^m 16^s and Dec +41°18′45″) of O stars. The cyan and bright green markers are known members of O- and B-type stars, respectively, in the OB2 association (Wright et al. 2015).