M. symmetochus was discovered by William M. Wheeler in late July 1924 in the fungus gardens of the attine Sericomyrmex amabilis of Barro Colorado Island.

[2] Workers are 3 to 3.5 mm long, with small, feebly convex eyes, that are probably adapted to living within the dark fungal gardens of their host.

Workers are yellowish red, with mandibles, funiculi, the posterior half of the first segment of the gaster and the sutures of the thorax and pedicels brown.

Males are brownish yellow, with a little darker gaster and slightly paler antennae and legs.

[5] Young queens stealthily invade fungus-growing colonies and start their own lineage in the fungus garden.

Also, these ants have been observed projecting their stings, leaving two isomers of 3-butyl-5-hexylpyrrolizidine, marking the nest with the scent of its toxin.