This spider has three pairs of humps on the back of its abdomen.
The male and female have a dark reddish-brown head and thorax and darker rings on the legs.
Zephyrarchaea mainae is a tiny spider about three millimetres long. Adults examined in 2012 measured 2.82–3.44 mm in males and 2.77–3.82 mm in females. Males have a tuft and an additional comb of hairs on the front of the chelicerae.
A hidden fork was discovered inside the male reproductive organ. A study published in 2021 examined one preserved male from Western Australia using micro-computed tomography to reconstruct the interior of its pedipalp, an appendage near the mouth used for sperm transfer.
The images revealed a sinuous sperm duct branching within the palpal bulb into two long, slender ducts, each leading to a separate outlet-bearing structure. In this species the secondary structure is relatively small and partly concealed. Three-dimensional imaging revealed an internal arrangement with two routes in a single appendage, extending what external observations alone had shown.
An extinction-risk assessment has not been added yet.
The 2012 species account identified fire, vegetation dieback, land clearing and climate change as threats. The Western Australian Department of Biodiversity, Conservation and Attractions’ South Coast regional conservation plan, published in December 2025, proposes biennial post-fire habitat surveys for this species and four other assassin spiders to assess whether they return after fire. Following the spiders and changes in their vegetation is therefore an explicit conservation priority.