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  Forest & Bird Magazine

Katipo threatened by changes to coastal sand dunes

Story and photo by Dr James Griffiths, a conservation scientist from Canterbury

The katipo spider has long aroused a sense of unease amongst New Zealand's beach users. Early Maori who named the spider 'night stinger' were loath to sleep in dunes at night and even now, tales of the dreaded katipo arouse anxiety amongst driftwood collectors or those contemplating a frolic in the dunes. Today, however, the likelihood of being bitten by katipo is becoming increasingly remote, as this icon of our coastal dune systems is rapidly disappearing.

Katipo belong to a worldwide genus Latrodectus which also includes the Australian red back (L. hasselti) and black widow spider (L. mactans). There are two recognised species of katipo; Latrodectus katipo and L. atritus. Both are peculiar to New Zealand and can be distinguished by the coloration of adult females.

Adult female L. katipo (Left) are primarily velvet black with the exception of a bright red dorsal stripe and a distinctive red, hourglass-shaped marking on the underside of the abdomen. The body is about the size of a pea. In contrast, adult female L. atritus, although almost identical in colouration and size, lack the red dorsal stripe, and the red hourglass on the underside of their abdomen is less distinct.

Compared to their female counterparts, mature male L. katipo and L. atritus are diminutive in size (one sixth the size of adult females) and are not so easily distinguished. Males of both species are predominantly white with a series of red-orange diamonds running along the dorsal region of the abdomen. These are bordered on either side by irregular black lines.

L. katipo and L. atritus have distinct distributions. L. katipo inhabits dune systems from New Plymouth and East Cape in the middle of the North Island as far south as Karamea and Dunedin in the South Island. L. atritus inhabits dune systems from New Plymouth and East Cape to Cape Reinga. Some overlap in distribution currently occurs around East Cape and New Plymouth.

Both species commonly establish webs in low-growing dune plants or driftwood. Webs are almost always constructed over open sand. Spiders inhabiting dune grasses, for example, construct webs in open spaces between grass tufts, whereas those inhabiting prostrate shrubs build webs on the underside of the plants overhanging open sand. Katipo are rarely found in dune regions where dense marram or other exotic plants such as kikuyu or buffalo grass cover the ground.

Research into the distribution and habitat preferences of katipo indicates that patches of open sand are necessary for katipo to build their webs, and that aggressive introduced plants that swathe dune systems in dense cover create an environment unsuited to web construction. Furthermore, katipo are rarely recorded from habitats other than dune systems, which implies that dunes modified by agriculture, forestry or urban development also fail to provide suitable katipo habitat.

These findings indicate that the introduction of aggressive exotic plants to New Zealand's coastal sand dunes, in combination with dune modification resulting from agriculture, forestry or urban development may have led to the reduction and fragmentation of katipo habitat. Ultimately, these factors are likely to be responsible for the decline in katipo numbers and may threaten the long-term survival of these species.

Unless steps are taken to conserve our coastal dune systems, the katipo is likely to become no more than an 'urban' legend. Conservation of coastal dunes will not only safeguard the future of our coastal icon, the katipo, but will also protect a rich flora and fauna that is as unique to New Zealand as our forests and birds.


South African Invader

In some dune systems, katipo may also be threatened by Steatoda capensis, a South African spider. It is shiny black and may have a dash of red, orange or yellow on it abdomen, thus its popular name 'false katipo'.

S. capensis produces more offspring than katipo and can breed throughout the year, (Katipo only breed in late spring and early summer.) Furthermore, S. capensis is not confined to coastal dunes but is commonly found under wood, debris and other objects, large distances from the coast. Because of these factors, S. capensis, is able to colonise driftwood and flotsam more quickly than katipo, following disturbances such as large storms, and under certain conditions may displace katipo from driftwood habitat in dune systems.



 


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