DLM and DVMs are scant. Myofibrils are disorganized, with variable fiber diameter, and Z bands are crooked.

70% of flw² flies are viable; 100% are flightless; 70% can make small jumps of less than 1cm while the remaining 30% cannot jump. In 90-95% of flies, the wings are held ventrolaterally at an angle ranging from 5^o to 30^o and 5^o to 60^o laterally - these angles increase following emergence. In 2-3% of flies, wing position is normal. Excitation of flw² flies results in wings being raised into the vertical position; in most mutants the wings return to the depressed state after a few minutes, while up to 5% of flies continue to hold their wings in the vertical position.

In many flw² flies, the posterior cross-vein is incomplete, the anterior scutellar bristles are missing and the eyes are slightly roughened.

Dorsal longitudinal fibres (DLMs) 1-4 and dorsoventral fibres (DVMs) 7-9 are absent in all flw² flies. DLMs 5 and 6 are present in the 2-3% of flw² flies that hold their wings in the normal position. Most mutants contain DVMs 10-13 but about 10% contain no indirect flight muscle fibres at all. The tergal depressor of the trochanters (TDTs) appear normal. In some flw² mutants structures resembling larval fat-body cells are found in the thorax.