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.