Smn^E33 mutant larvae exhibit a decrease in locomotion but are more responsive to tail stimuli (i.e. touching of the tail), with a greater number of tail flips, specifically. There is no difference in response to head or abdomen stimuli, compared to controls.

Smn^E33 mutant flies are flightless.

Smn^X7/Smn^E33 third instar larvae have significantly increased evoked excitatory postsynaptic potential amplitude at the neuromuscular junction.

100% of homozygous adults are incapable of flying or jumping.

The mutant indirect flight muscles (IFMs) are highly disorganised; the mutant dorsal longitudinal muscles (DLMs) often fail to extend the whole length of the thorax in contrast to wild type and dorsoventral muscles (DVMs) are typically unidentifiable. The mutant muscles show clear signs of degeneration and are extremely irregular with numerous bulges and constrictions throughout. The mutant myofibers do not show the characteristic striations normally seen in wild-type myofibers. Thick filament formation is largely unperturbed in the mutant indirect flight muscle fibers, while thin filament formation is disrupted.

The number and routing of primary branches of the DLM motoneurons are severely compromised in mutant adults. Secondary branches are disorganised, with arborisation defects ranging from moderate to severe.