The Ministry for Primary Industries (MPI) is looking for the person who posted a foreign ant to an insect scientist in Auckland, but failed to provide any contact details.
The ant was packaged inside a small plastic jar addressed to the Landcare Research scientist with a note that said "Hi, here is an ant I found at the beach" with an illegible signature.
The insect has since been identified as an Australian species of carpenter ant - the "golden sugar ant" - of which there is no established species in New Zealand.
Should it be introduced, the potential impacts are uncertain, said MPI's plants and environment incursion investigation manager Mark Bullians.
"We know some species of carpenter ants can cause structural damage to wooden buildings as they chew out holes in wooden materials to build their nests. This particular ant may also have potential for environmental impact as, if established here, it could build nests in native trees and compete with native insects and birds for food," Bullians said.
"For these reasons, we're very keen to hear from the sender of this ant sample. We would like to find out more about the location the ant was found so that we can carry out an investigation and ensure that if there are further ants, they are located and destroyed."
Since the package's arrival late last year, MPI has had no luck trying to find the sender.
The ant arrived in a courier envelope brought by a courier contractor in Te Aroha, leading the ministry to believe that the insect may have come from somewhere in the Waikato.
Landcare Research has also appealed to all of its usual submitters for information but have received no response.
"After exhausting all possible means of locating this person, we appeal to the public for support in this search. It may be that the ant was dead when found and had been caught up in someone's shoes or outdoor/camping gear that had been used overseas. We're optimistic that it is a single one. But we'd like to have some certainty."
Anyone with information, or who has seen any unusually large ants - particularly at the beach - is asked to contact MPI's pest and disease hotline on 0800 80 99 66.