Northland Regional Council biosecurity manager, Don McKenzie, said the larger female spiders are responsible for almost all redback bites, although it's rare for them to attack. It usually only happens if they are disturbed or trapped in clothing.
Bites could be painful, but no deaths have been attributed to a redback bite in Australasia since an anti-venom was developed more than 50 years ago.
McKenzie said the regional council's role with redbacks is limited to any biosecurity risks they might pose.
"However, we think it's a common sense to point out - to Kaipara residents in particular - that given this discovery they might like to take a little bit extra care when working in and around sand dunes, under old logs, and in back yards, as the spider can hide under garden implements and sheds."
Redbacks typically hide in dark, dry, sheltered spaces and are most active in the late afternoon and evening.
They can be distinguished by an orange or red stripe on their backs and a distinctive hour-glass shape on the bottom of their abdomen.
"The bite reportedly causes a sharp pain similar to a pinprick and may lead to localised redness, pain and sweating," said McKenzie.
Occasionally the pain and sweating may spread and stomach pain may occur. Symptoms can also include aches in muscles and joints, nausea and vomiting, and increased heart rate and blood pressure.
McKenzie said anyone who thinks they may have been bitten by a redback should seek urgent medical treatment.
Anyone in Northland who finds or suspects a spider is a redback should call MPI on its pest and disease hotline (0800 80 99 66).
