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Mr Harris said it was most common for people to come across large spiders in their homes in November or early December when mature males were looking for females to breed with.
Large male tunnel web spiders were commonly found in homes and while their bite could be painful, the pain usually only lasted a few minutes.
Vagrant spiders (an Uliodon species) could also wander inside and their bite could be more serious.
''Bites from Uliodon species ... can cause severe problems in some people, lasting for over a year.''
The slater-eating spider Dysdera crocota can give a ''sharp nip'' but the pain soon disappears.
Four other Dunedin species from the genus Steatoda, with dark abdomens the size of a pea, can give a bite with pain that lasts up to four days. The Steatoda spiders - accidentally introduced from South Africa - were often found inside.
White-tailed spiders had a bad reputation but their bite usually caused no problems, Mr Harris said.
The katipo spider (Latrodectus katipo) is found in North Otago coastal areas. A bite can be fatal but only about 2% of people bitten, and not treated with anti-venom, die.
The larger Australian redback spider (Latrodectus hasselti) is closely related to the katipo and its bite has a similar effect. About 2% of untreated people (usually elderly, sick, or very young children) died from its bite, Mr Harris said.
''In general, it is best to avoid holding spiders in one's hands.''
A bite can be recognised by two small puncture marks, where the spider's fangs have broken the skin.