Is it a katipō? New Zealand's venomous spiders and their look-alike

Which New Zealand spiders are actually venomous to people

Only two, the katipō and the redback, which are both widow spiders in the genus Latrodectus. The National Poisons Centre names them as the only New Zealand spiders that pose a threat to people, and says the venom of the others, the white-tail included, has no known harmful effect on people. Size and colour alone will not tell you whether a spider is venomous, but these three can be told apart.

The white-tail is the spider most often blamed for a bad bite, but Health New Zealand does not class its bite as poisonous, and the clinical evidence agrees. We have summarised what the evidence says about white-tail bites separately.

Why the katipō is protected, and what that means for you

Katipō numbers have fallen sharply as dunes were grazed, burned, planted in pine, churned up by recreation and smothered by introduced marram grass, and the Wildlife Act 1953 now gives the spider Absolutely Protected status. A national survey for the Department of Conservation, published in 2002, found katipō at only 46% of the sites where it had previously been collected. It is a declining native animal, not a pest.

In practice that means leaving it where it is. We will not treat, kill or remove a katipō, and nobody else should either. On the beach, wear shoes in the dunes, shake out towels and bags that have been lying in the grass, and keep children's hands out of the base of the beach grasses where katipō web. If you would like to record a sighting, your local Department of Conservation office is the place to tell.

The katipō has a competitor as well. The false katipō, introduced from South Africa, uses the same kind of beach habitat, and Te Papa notes it may have displaced the katipō on some beaches.

The false katipō, which is the one you have probably found

The false katipō, or black cobweb spider (Steatoda capensis), is glossy black to dark brown and about the size of a katipō, and some have a faint red stripe. What gives it away is the pattern of white markings on the abdomen and the absence of a red hourglass underneath. Unlike the katipō, it lives in and around houses, sheds and gardens all over the country, as well as on beaches.

Te Papa notes its bite can be quite painful and may leave someone feeling unwell for a day or so, but it is not considered dangerous. Around a house, a false katipō is an ordinary spider and is dealt with as part of a normal spider treatment, which is the one situation where you will hear us offer to treat a black spider.

After a katipō or redback bite: first aid and who to call

Keep the person calm, wash the bite with soap and water, cool it with ice in a tea towel, and ring the National Poisons Centre (0800 764 766) or see a doctor promptly. Ring 111 if breathing becomes difficult. Health New Zealand advises against pressing on the bite, and against any alcohol afterwards.

Signs worth describing when you call include pain that spreads out from the bite and gets worse, sweating, stomach pain or cramps, nausea and aching muscles. Hospitals hold antivenom for widow spider bites if it is needed. Bites are rare, and Te Papa notes that the deaths once put down to katipō rest on doubtful records from the 1800s, but a bite can still make someone very unwell, so do not wait to see how it develops.