Ninja-Star Ceiling Spider Identification in Australia

About the Ninja-star ceiling spider

The ninja-star ceiling spider, Zosis geniculata, is a small hackled orb-weaver found in sheltered parts of Australian buildings, especially in subtropical and tropical areas. It is best recognised by a combination of characters: an adult only a few millimetres long, black-grey-white banded legs, a pale mottled abdomen that is humped in females, a damaged-looking cribellate orb web and, when present, a flat pink to light-purple egg sac with five to eight pointed corners. The “ninja star” is the egg sac, not the spider’s body. A ceiling location or messy web alone is not enough for a species identification. The World Spider Catalog uses the accepted feminine spelling Z. geniculata because Zosis is feminine; the Australian Faunal Directory and some Australian Museum captions still display the historical spelling Z. geniculatus. Both spellings refer to this same species in those sources.

Exact-species specimen views

These licensed exact-taxon photographs show useful anatomy and variation. Use each caption for record and image context; no single image set represents every colour, posture or habitat.

How to identify Zosis geniculata

Start with scale and body form. Opell’s taxonomic revision measured adult males at 4.0–6.3 mm and females at 6.3–8.4 mm in total body length. The female has an elongated oval abdomen with a single median hump in its front third; the male abdomen is smaller and smoother without that tubercle. The front body ranges from grey to reddish brown, the abdomen is often pale grey-white with darker mottling, and recent diagnosis work highlights the conspicuous black, grey and white leg banding. In a clear photograph, the female’s fourth metatarsus is noticeably curved and carries the calamistrum, a row of specialised hairs used to comb extraordinarily fine cribellate silk. Those minute structures are specialist or macro-photo characters, not something to test by touching the spider. In a home, the best practical evidence is the adult form plus the web and pointed pink egg sac. Genital examination remains the firmer species test where the photograph lacks the sac or diagnostic dorsal view.

Clues that are not enough on their own

• A ceiling or wall-corner location on its own; daddy-long-legs, cobweb spiders and wall spiders also use buildings
• A generally messy web; the useful clue is a damaged or obscured orb at the heart of older cribellate silk
• Grey-brown colour without a sharp dorsal photograph, because lighting and dust make many small house spiders look similar
• A star-like object without confirming that it is a pink pointed silk egg sac rather than debris, shed skin or another uloborid sac
• Long banded legs alone; combine them with the female hump, adult size, web structure and egg-sac shape

Colour, sex and life-stage variation

Sex, maturity, lighting and background change the appearance substantially. Females are larger and usually show the anterior abdominal hump; adult males can be nearly half the female’s mass, with a narrower oval abdomen and enlarged palps. Opell described the carapace from grey to reddish brown and the abdomen as usually white without strong markings, while modern Australian exact-species photographs show heavy grey-brown mottling and sharply banded legs. A spider backlit on a white ceiling can therefore look almost black, and a flash photograph can exaggerate the white bands. Newly made egg sacs are pinkish to light purple, but dust, age and empty silk can make them beige or grey. The licensed hero image on this page is an exact-species Australian observation showing the adult and banded legs; the second exact-species Australian image shows the pointed egg sac. Neither image proves the identity of a different spider by itself.

Behaviour, web and retreat

This spider remains in a capture web rather than hunting across the floor. At the centre is a true orb, but the web often stops looking neatly circular: hackled orb-weavers push old damaged sections aside instead of eating and recycling them, and add fresh silk, debris and thin hub decorations. The capture threads are cribellate—dry, wool-like fibres that snag insect legs mechanically rather than glue droplets. When prey hits, Z. geniculata can jerk the web, approach cautiously, turn away and cast silk with its fourth legs. Because uloborids lack venom glands, they immobilise prey under dense wrapping silk and apply digestive fluid before feeding. Older taxonomic observations describe a thin pink-to-purple egg sac containing roughly 40–80 eggs, with five to eight support points, left in the orb mesh. The Australian Museum calls the sac asterisk-shaped and says egg sacs are usually guarded; a later peer-reviewed study found Z. geniculata kept sacs attached to the web until spiderlings emerged. Guarding posture may vary, so the absence of a female beside a sac does not rule it out.

Australian distribution

The World Spider Catalog treats Zosis geniculata as native from the southern United States to Brazil and records it as introduced across many warm regions, including Australia and Pacific islands. Australian Museum describes it as pantropical, possibly introduced, and most characteristic of Brisbane and other subtropical or tropical Australian sites. An Atlas of Living Australia query against the exact Australian Faunal Directory taxon concept returned 556 occurrence records at review time: 452 from Queensland, 65 from New South Wales, nine from Victoria, three from the Australian Capital Territory, two from South Australia, one from the Northern Territory and 23 without a supplied state; one overseas record was also grouped in the facet. These are aggregated occurrence records, not population counts or proof that every identification is correct. The page filters therefore emphasise the recorded eastern and northern range and do not infer Western Australian or Tasmanian presence from family-level maps.

What to do if you find one

Leave the spider and web in place if the corner is suitable: it catches small insects and is not a venom risk. For identification, do not rely on a ceiling silhouette. Take a dorsal close-up, a side view that shows the female’s hump, a wider frame showing whether an orb remains within the messy silk, and a separate sharp image of every egg sac. Place a ruler near, not in, the web. If removal is necessary, wear gloves, place a broad container beneath the spider and web, then use stiff card or a soft brush on a long handle to guide the spider in; move it to a dry sheltered outdoor structure. Egg sacs may contain live young, so relocate them with their supporting silk or remove them only if that outcome is intended. Regularly clearing abandoned silk and sealing gaps reduces recolonisation. Do not spray an occupied web merely to obtain a closer photograph, and do not publish a precise private-property location.

Compare with similar spiders

Use body shape, web or retreat, location and behaviour together before settling on a likely match.

• Daddy-long-legs spider — Daddy-long-legs spider - Pholcus phalangioides has extremely long, threadlike legs, a tiny elongated body and a loose three-dimensional tangle rather than a hackled orb. A female carries a rounded cluster of exposed eggs in her mouthparts instead of leaving a flat pink pointed sac in the web.
• White porch spider — White porch spider - Cryptachaea gigantipes is a comb-footed cobweb spider with a more rounded abdomen, very long fine legs and an irregular tangle web, often with a leaf retreat. It does not make the characteristic pink five-to-eight-pointed Zosis egg sac.
• Red house spider — Red house spider - Nesticodes rufipes is usually reddish brown with a rounded abdomen and fine unbanded-looking legs in a disordered indoor cobweb. Check body colour and shape, then look for the central orb and pointed pink egg sac before calling a spider Zosis.
• Wall spider / baseboard spider — Wall spider / baseboard spider - Oecobius navus is much smaller and flatter, darts across walls and lives beside a compact lace-like disc retreat on the surface. It lacks the suspended altered orb, humped female abdomen and pink star-shaped egg sac of Z. geniculata.

Sources for this profile

These accessible authoritative sources support the identification and bite-safety context on this page.

• Australian Museum: Hackled orb-weavers
• Australian Faunal Directory: Zosis geniculatus
• Atlas of Living Australia: Zosis geniculatus occurrence records
• World Spider Catalog: Zosis geniculata
• Opell 1979: taxonomic revision of Uloboridae
• de Luna et al. 2023: diagnosis of Zosis geniculata
• Barrantes et al. 2013: egg-sac ecology
• healthdirect: Spider bites

Profile review

Published by Spider Identifier Australia. Last factual review: 11 August 2026.