Mick Whittle
Imagine New Zealanders being out-competed by South Africans on home soil, or big burly Kiwi blokes being beaten at their own game by smaller, faster Australians.
No, we’re not talking sport here, we’re talking spiders – in particular, the native New Zealand katipo.
A venomous widow spider, related to the infamous North American black widow and the Australian redback, the katipo occurs throughout New Zealand, predominantly in coastal areas, in grasses and under driftwood.
The Maori name, meaning ‘‘night stinger’’, possibly arose due to katipo bites received while collecting wood for evening fires.
It has also long been believed that the population of katipo, given protected status in 2010, is declining, with one of the possible causes being competition with its invasive relative, the South African ‘‘false katipo’’, first recorded here in the 1940s.
This fall in population appears to be backed up by a recent study in the NZ Journal of Zoology by Simon Hodge and Cor Vink, of Lincoln University and Canterbury Museum respectively, in which they report an apparent decline in katipo numbers at sites where they were previously found.
The study, part of a larger three-year survey of insects and spiders on the beaches of Banks Peninsula, found that while false katipo were relatively common in sites in Christchurch’s seaside suburb of New Brighton, true katipo were conspicuously absent. Previous studies, however, had reported the clear presence of the New Zealand species in these locations.
According to Vink, the museum’s curator of natural
Genetic evidence of interbreeding between the New Zealand katipo and the Australian redback is about to be presented. reports on this arachnid battle of the sexes.
history, the range of the false katipo is far wider than that of its New Zealand cousin, with the South African spider being especially common around dwellings.
Human activity, including buildings and other modifications to the coastal environment, could possibly account for the apparent decline in katipo numbers. Sheer weight of numbers, therefore, rather than direct aggressive competition might explain the seeming expansion of South Africans at the expense of the Kiwis.
But while Kiwis might be somewhat reassured that it is not strength or skill giving the South Africans an advantage in this particular case, another threat from another of New Zealand’s sporting rivals also looms for the beleaguered katipo, this time from the Australian redback, also a recent arachnid arrival. This threat, moreover, strikes straight at the macho heart of New Zealand males’ sexual prowess.
The latest DNA research suggests that the genetic distance between the katipo and the redback – that is, the time since these two species diverged – is relatively recent, possibly within the last few hundred thousand years, with ancestral katipo likely to have ‘‘ballooned’’ to New Zealand on threads of web carried by the wind. Given this close genetic relationship, katipo and redbacks can still interbreed, but with one important qualification.
Male katipo are considerably larger than their Australian counterparts and, in laboratory experiments, female redbacks simply regard the former as prey, with the unfortunate male katipo invariably ending up as lunch rather than as a mate. Male redbacks, however, face no such problem, with female katipo happily mating with the sneaky little Australians.
With redbacks established in New Zealand since at least the 1980s, especially in warm, dry, grape-growing regions, the possibility exists that the Australian interlopers may interbreed with native katipo – specifically, that Aussie males may increasingly elope with Kiwi females.
Next month, at a joint NZ/ Australian Entomological Society conference, Vink will present the first genetic evidence that this has indeed occurred in the wild.
But while the katipo itself potentially faces threats from both South Africans and Australians, what about the threat these spiders pose to human beings, especially given the notoriety of the redback and the fact the venom of widow spiders contains powerful neurotoxins?
As an arachnologist, Vink is bemused by the widespread dread of fatal spider bites, pointing out that bee stings can also sometimes prove deadly. And widow spiders such as the katipo and the redback are not particularly aggressive, usually biting only if their nests are disturbed.
The real problem for anyone unfortunate enough to be attacked is the extreme pain the neurotoxins cause, Vink says.
‘‘If you’re bitten, you won’t die but you’ll feel like you want to.’’
In all reported cases of redback bites, only a dozen or so people have died, with the very young or very old, and obese or unhealthy people, most at risk. In New Zealand, the last known fatality from a katipo bite was in ‘‘preTreaty of Waitangi times’’, Vink says.
A more recent reported katipo attack, reported in the British Daily Mail under the headline, ‘‘Skinny dipper bitten on manhood by deadly New Zealand spider’’, involved a naked Canadian tourist in 2010. And as only the female bites, the unfortunate tourist also proved that, unlike Australians, Canadian males are clearly far too large. Nevertheless, whether or not the katipo is in serious decline and, if so, whether false katipo and redbacks are a likely cause, has yet to be conclusively determined.
According to Hodge, New Zealand lacks the long history of insect and spider collectors, many of them amateur, found in places like the UK. His own study, for example, which concentrated solely on beaches in a limited area, has amassed collections of not just spiders, but also numerous species of flies, wasps and beetles, with full analysis of the results likely to take years.
And while New Zealand’s larger fauna, particularly the birds, has been well researched, much of the country’s invertebrate fauna still awaits discovery or detailed research, Vink says.
‘‘Even some large spiders [in New Zealand] have not yet been named.’’