New Zealand has a very small number of poisonous and venomous animals. The grey side-gilled sea slug (Pleurobranchaea maculata) is an example of a poisonous animal. It is toxic when eaten. Venomous animals inject their toxins via a bite (for example, spiders) or sting (for example, wasps). Deaths are rare, but appropriate treatment should be given when people have been exposed to toxins to ensure a satisfactory outcome for the patient.
New Zealand is home to about 2,500 kinds of spiders, most of them harmless to people. Only some spiders are capable of biting humans.
There are three species of spiders in New Zealand that should be avoided – the katipō, the redback and the white-tailed spider. The katipō is native to New Zealand, while the redback and white-tailed spider came from Australia.
The katipō (Latrodectus katipo) and the redback spider (Latrodectus hasselti) belong to the same genus as the American black widow spider. These two are the only venomous spiders found in New Zealand. In both species, it is the adult females that are capable of biting humans. Bites from these spiders are not common, as by nature they are shy non-aggressive animals. Bites from both species are extremely rare, and there is a safe and effective anti-venom for both redback and katipō bites.
White-tailed spiders (Lampona cylindrata and Lampona murina) are Australian natives that arrived in New Zealand in the late 19th century. The white-tailed spider bite can be painful, but the initial burning feeling, swelling, redness and itchiness at the bite site usually goes and there are no long-lasting effects. Media attention and medical reports have suggested that bites may cause necrotic ulcers (destroyed skin). However, an Australian study (2003) has shown no evidence linking necrotic ulcers to white-tailed spider bites. White-tailed spider bites are not considered venomous to humans.
The discovery of tetrodotoxin in the grey side-gilled sea slug has made this native sea slug our most toxic creature.
The bluebottle jellyfish, also known as the Portuguese man-of-war (Physalia physalis and the slightly smaller Physalia utriculus), is our most venomous jellyfish. Despite its outward appearance, the Portuguese man-of-war is not a true jellyfish but a siphonophore (a colonial organism made up of many minute individuals). True jellyfish are single organisms.
All jellyfish (including the Portuguese man-of-war) have microscopic stinging cells called nematocysts. These structures are numerous on the tentacles or body of the animal and are used to capture prey. A small dose of venom is contained within each nematocyst. A sting from a Portuguese man-of-war jellyfish will most likely result in nothing more than localised pain and itchiness. Characteristically, stings cause a linear collection of weals, with a surrounding red flare. Extensive stinging (more likely from larger specimens) may lead to symptoms including nausea, vomiting, headache, chills, drowsiness, breathing difficulties, cardiovascular collapse or death – though such symptoms are very rare.
Stingrays are also capable of giving a venomous sting, but this is rare because they generally do not attack humans unless provoked. The majority of injuries from stingrays are to the lower limbs and usually occur when swimmers or divers accidentally step on them.
New Zealand’s coastal waters are host to a range of venomous fish and sea urchins. Most of these fish are classified within the Scorpaenidae family (scorpion fish) and come in a wide variety of sizes, shapes and colours. They include the spiny dogfish (Squalus acanthias), elephant fish (Callorhinchus milii) and the brown bullhead catfish (Ameiurus nebulosus) – an introduced freshwater catfish. These venomous fish have external spines and all produce a similar toxic response in victims. Exposure to toxins can result in severe local pain, which can spread to the whole of the affected limb. In rare instances, sea urchin stings induce a delayed-type hypersensitivity reaction.
For most people, a sting from these common insects will result in pain, itchiness, redness and minor swelling around the sting site. Symptoms usually subside after a few hours.
Bee and wasp venoms are a complex mix of proteins, serotonin and histamine. It’s the histamine that causes pain and swelling. Medical help is usually only necessary for stings in the mouth and throat and for hypersensitive and allergic people (0.5–2% of the population). On average, two people die from wasp or bee stings every 3 years in New Zealand.
In this activity, students learn about toxins and poisons and research what’s poisonous in New Zealand.