Invasive ants
Over 160 ant species have established outside their native range (see McGlynn 1999 for a recent list although many in his list for Hawaii are quarantine interceptions only).These include “tramp” species that have been spread throughout the world by human transportation and are often pests in urban environments.
Among the tramp species are several with the potential to invade native habitat in a new country and have an impact on the native fauna (e.g., Porter & Savignano 1990; Human & Gordon 1997; Hoffmann 1998). This last group we particularly do not want in New Zealand and we need management strategies to minimise the detrimental impacts of those already here.
Some of the worst global ant pests
The species listed below are some of the worst ant pests. New Zealand may not be climatically suitable for some tropical species.
| Species | Nests found in New Zealand | Established in New Zealand |
| Anoplolepis gracilipes Yellow crazy ant |
yes | no |
| Linepithema humile Argentine ant |
yes | yes |
| Paratrechina longicornis Crazy ant |
yes | no? |
| Pheidole megacephala Big headed ant |
yes | yes |
| Solenopsis geminata Tropical fire ant |
no? | no |
| Solenopsis invicta Red imported fire ant |
yes | no |
| Wasmannia auropuntata Little fire ant |
no? | no |
Assessing the threat to New Zealand
A risk assessment scorecard was developed to quantify the threat to New Zealand of a range of ant species. 75 taxa were scored and grouped as high, medium, or low threats. A summary was prepared for each taxa, outlining why it was considered for assessment, and any mitigating factors that might reduce the risk of the taxa establishing in New Zealand (e.g., not climatically suitable) (Risk Summary 
559 KB).
Information sheets were prepared for all taxa scored as medium- or high-risk threats to New Zealand.
NB. The red imported fire ant (Solenopsis invicta) is considered to be the worst ant pest in the world. It has the potential to become a significant environmental, economic and human health hazard should it ever become established here. However, Solenopsis invicta was specifically excluded from consideration in this risk assessment as this species has already been subject to detailed consideration by Biosecurity New Zealand (Download report 1.2 MB).