Threats

Parasitism, predation, and habitat loss are the key threats to our native butterflies.

Habitat Destruction

Nettle Removal. Photo; C. Rayz

Nettle Removal. Photo; C. Rayz

Our native butterflies rely on key plant species for their survival during the larval stage, so the removal of certain plants can sound the death knell for certain species. Unfortunately, many plants that are appropriate food plants are also considered weeds. For example, Muehlenbeckia, which Copper caterpillars rely upon, was until recently commonly removed from urban areas because it was seen as a tripping hazard or an unsightly vine which sprawled over ‘more attractive’ shrubs. And nettles – which are essential for the survival of Admiral caterpillars – are distinctly unfriendly stinging plants to have in a garden or public place. Understandably, many of these have been removed, but the butterflies are suffering for it. Educating people about why these plants are important as well as planting them in safe places will allow native butterflies to thrive once again.

Wasps

Black European Wasps are ket predators of native butterflies. Photo: John Tan

Black European Wasps are ket predators of native butterflies. Photo: John Tan

Wasps can be serious predators of butterfly caterpillars. Typically the wasps infect their hosts by laying their eggs inside the caterpillars. When the eggs hatch, the caterpillar is eaten from the inside and usually dies when it's about to form a chrysalis.

The yellow and black European wasps (Vespula) are widespread and especially common in the Nelson-West Coast region. The brownish Australian paper wasp (Polistes humilis) and the more recently arrived black and yellow Chinese paper wasp (Polistes chinensis) likewise feed regularly on caterpillars.

Two species of wasp, the Chalcid Wasps (Pteromalus puparum), and Apanteles glomeratus, that were introduced as a biocontrol agents to decrease numbers of the white cabbage butterfly, however they began to parasitize native butterflies too.

The White-spotted Ichneumon (Echthromorpha intricatoria) a self-introduced wasp species from Australia, that parasitizes the chrysalis of Admiral butterflies and also accounts for many deaths of these butterflies. Parasites are a natural and necessary part of any ecosystem, but coupled with habitat loss and the introduced wasps, parasitism can take a heavy toll on the already strained butterfly population.

Parasitic Flies

There is one type of parasitic fly parasitises our native butterflies. Not a lot known about the it, although a Tachinid fly of the genus Pales has been seen to parasitise Glade Copper caterpillars. The flies lay their eggs onto the leaves of their foodplant so that the caterpillars eat the fly eggs and eventually these fly larvae eat the caterpillars from within. 

Historical Threats

Many of the native butterflies were also taken out by the aerial spraying that occurred in the 80s and 90s aimed at removing moths that were eating pine tree and timber crops.