These stick insects are fairly small, with the body size of females reaching up to 4.8 cm long.

Males are smaller and skinnier, appearing only faintly ridge-backed, and with less prominent "teeth" on the legs compared to the female.

[2] An interesting character is that the eggs of Spinotectarchus acornutus are covered in short spines giving it a hairy appearance.

[1] Studies have shown that S. acornutus is unrelated to other stick insect genera in New Zealand.

They can be most commonly found on Metrosideros perforata (climbing rata), Dendroconche scandens (fragrant fern), the epiphyte Collospermum hastatum, and Dysoxylum spectabile (kohekohe).