A series of traditional and modern morphological techniques were used to examine and document the thoracic skeletomuscular structures in detail of the flightless insects from BIG4 orders: Lepidoptera, Coleoptera, Diptera and Hymenoptera. The flightlessness of female Nyssiodes lefuarius (Lepidoptera: Geometridae) with an independent evolution background is linked not only with the modifications of flight related skeletomuscular structures, but also with the enlarged ovaries and the reduced digestive system. The evolutionary scenario of flight ability enhancement in Lepidoptera is demonstrated using the combined morphological characters mapping on the phylogenometric topology. The extremely simplified thoracic skeletomuscular structures and a well-developed swimming apparatus of Orectochilus villosus (Coleoptera: Gyrinidae) were clearly demonstrated. The limited skeletomuscular elements take over more functions to support the flight capacity. The strongly flattened thorax and the specialized leg structures of Crataerina pallida (Diptera: Hippoboscidae) adapt to the ectoparasitism. The flight related skeletomuscular structures are strongly modified as the reason of the flightlessness of this species. The monophyly of Hippoboscoidea is supported based on morphological parsimony analysis. The thoracic skeletomuscular system of workers of Myrmecia nigrocincta (Hymenoptera: Formicidae) was examined. The primitive status of Myrmeciinae was challenged based on recent researches from both morphology and phylogenomics. The strongly modified thoracic structures of the worker ants support the entire family as an ecologically dominant group. Parsimony analyses support a sister group between Strepsiptera and monophyletic Coloptera. Archostermata is recovered as the sistergroup of the remaining suborders of Coleoptera, and Polyphaga as the sister group of Myxophaga. The Bayesian analyses based on the same morphological dataset provide a different topological pattern.