Spider bites

Do white-tail spider bites really cause flesh damage?

Q: Where did New Zealand's white-tail spiders come from?

No. Both of New Zealand's white-tails come from Australia. Lampona murina, the North Island species, was first recorded at Waiwera, just north of Auckland, in 1886, and has been established ever since. Lampona cylindrata is the South Island species and, according to Te Papa, has become widespread there since about 1980. Both hunt other spiders, and both are most often met indoors.

Do white-tail spider bites cause necrosis? What the 130-bite study and the Christchurch Hospital review found, what a real bite does, and when it needs a doctor.

The short answer

No. In the largest study of confirmed bites, 130 people whose spider was caught and identified, not one developed a necrotic ulcer, and a review of patients at Christchurch Hospital found no sign of flesh damage from spiders either. A white-tail bite is genuinely painful and often leaves a red mark for about a day, but its venom is not considered dangerous to people. White-tails eat house spiders, which is why spider control around the house reduces them.

What the 130-bite study found

Isbister and Gray (Medical Journal of Australia, 2003) followed 130 bites in which each spider was caught at the time and named by a specialist. None of the 130 developed a necrotic lesion. Every bite hurt, and about a quarter hurt severely; 83% left a red mark, 9% brought brief general symptoms such as nausea or a headache, and the effects lasted a median of 24 hours.

Of those bites, 79 were from Lampona cylindrata and 51 from Lampona murina, which is the white-tail of the North Island, so the result applies to the spider Aucklanders find. The authors concluded that white-tail bites are very unlikely to cause necrotic ulcers, and that when an ulcer does appear, a doctor should look for another cause.

The New Zealand evidence

Banks, Sirvid and Vink (New Zealand Medical Journal, 2004) went through suspected spider-bite admissions to Christchurch Hospital from January 2001 to January 2003, and found that none showed evidence of necrotising arachnidism, the flesh damage white-tails are blamed for. Manaaki Whenua, which summarises both studies, concludes that public fears about the bite are misplaced.

Te Papa's spider specialists reach the same view: there is nothing in white-tail venom of particular concern for people, and Health New Zealand does not regard the bite as poisonous. Calling the spider poisonous, as older articles do, is simply wrong.

What a real white-tail bite looks and feels like

The bite hurts straight away, a sharp pain like a sting. A red mark and some swelling usually follow, with itching or a burning feeling at the spot, and in most people it settles within a day. In the Australian study, 44% were left with a sore, red patch that lasted longer, occasionally for several days.

The spider itself is easy to catch afterwards, because white-tails have poor eyesight and do not run far. Trapping it under a glass and keeping it in a jar is the single most useful thing you can do, because a confirmed identification tells whoever treats you exactly what they are dealing with. On the site, a white-tail is 12–17 mm long, slim, dark grey, with a white tip on the abdomen.

Where the ulcers people blame on white-tails come from

When a wound does break down, the usual cause is a bacterial skin infection or a different condition altogether, and many of these cases were never spiders at all, because no spider was ever seen. Te Papa notes there is no evidence that white-tails pass bacteria on when they bite, although broken skin of any kind can pick up an infection if it is not kept clean. A doctor can tell these conditions apart; a photograph online cannot.

Other bites get blamed on spiders too, most often fleas and bed bugs, which bite repeatedly and leave several marks rather than one. If you keep finding new marks around the ankles, read about flea bites, and if they turn up in lines after nights in one bed, about bed bug bites. Neither is a white-tail problem, and neither is solved by spider spray.

First aid, and the signs that need a doctor

Wash the bite with mild soap and water or an antiseptic, then cool it with an ice pack or ice in a tea towel, kept off bare skin, to take the edge off the pain and swelling. That is the first aid both Health New Zealand and the Poisons Centre recommend. The Poisons Centre also says not to put vinegar or methylated spirits on the wound. For most white-tail bites, nothing more is needed.

See a doctor if the redness keeps spreading, the pain is getting worse, the bite blisters, weeps pus or turns into an open sore, or you run a temperature or start to feel unwell in yourself. For advice about any spider bite, ring the National Poisons Centre (0800 764 766), or Healthline, free and at any hour (0800 611 116). Ring 111 if anyone has trouble breathing or shows a serious allergic reaction.

If the spider was black with a red stripe, or the bite happened on a beach, treat it as a possible katipō or redback and ring the Poisons Centre straight away. We explain the differences in katipō and redback bites.

Fewer white-tails in the house

White-tails come indoors to shelter after hunting at night, and they follow their prey, the grey house spiders and black house spiders webbing the outside walls. So the practical way to see fewer of them is to reduce those webbing spiders on the eaves, window frames and fences, and to give white-tails fewer places to hide inside, especially in fabric left lying around.

Manaaki Whenua notes that they often hide in clothing left on the floor. Pick up clothes and towels, shake out shoes, gloves and gardening gear that have been outside, and in summer give the sheets a look before getting into bed. For the outside of the house, our guide on when to spray for spiders sets out the timing and the surfaces that matter.

Questions

White-tail spider questions

Where did New Zealand's white-tail spiders come from?

No. Both of New Zealand's white-tails come from Australia. Lampona murina, the North Island species, was first recorded at Waiwera, just north of Auckland, in 1886, and has been established ever since. Lampona cylindrata is the South Island species and, according to Te Papa, has become widespread there since about 1980. Both hunt other spiders, and both are most often met indoors.

Can a white-tail spider bite kill you?

White-tail venom is not considered dangerous to people, and neither of the clinical studies of confirmed bites found anything more serious than pain, redness and, in a few cases, brief nausea or headache. As with any bite or sting, a small number of people react strongly: ring 111 if anyone struggles to breathe, has a swollen face or throat, or feels faint.

Why do white-tails end up in beds and towels?

They hunt by night and then look for a dark, tight place to rest, and the folds of a towel, a sheet or a pair of jeans on the floor suit them perfectly. Most bites happen when someone presses a sheltering spider against their skin while drying off, dressing or getting into bed, not because the spider went looking for a person.

Should I keep the spider that bit me?

Yes, if it is safe to. Trap it under a glass, slide a card underneath and keep it in a jar. A confirmed identification tells your doctor or the Poisons Centre what they are dealing with, and it matters because so many so-called spider bites come with no spider at all, which is exactly how the white-tail got its reputation in the first place.

Do white-tails jump or chase people?

No. They are slow, wandering hunters with poor eyesight, and according to Manaaki Whenua they bite only when they are handled or provoked. A white-tail on a wall or the ceiling is not a threat. It is best moved outside under a glass, or left to carry on hunting the house spiders that brought it inside.

Sources

If you need someone

Fewer spiders around the house

Spiders and flies

Spider & Fly Control

Most of the spiders on an Auckland house belong to two introduced web builders, the grey house spider and its black cousin, and treating the eaves, window frames and fences they web is what brings the rest down, white-tails included, because white-tails hunt them.

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