Aliens in Our Backyard: Parasitoid Wasps (and How to Catch Them)

Posted by Tom Saunders.

The eponymous extra-terrestrial from the Alien film franchise struck terror into our souls –razor sharp teeth, acid for blood, and an unusual capacity for memorising the layout of ventilation shafts. But it had another interesting trait – it had a parasitoid life cycle. A parasitoid is an organism that spends its juvenile life stage feeding on the body of a host. While a parasite allows its host to live, a parasitoid does not. It emerges from its dead host in a similar way to how the alien bursts out of the chest of a helpless crew member. But while the ‘xenomorph’ was a frightful fantasy dreamt up by Hollywood, parasitoid wasps are important creatures that live all around us, and we should try to understand them.



Lemon tree borer parasite (Xanthocryptus novozealandicus), a native New Zealand parasitoid wasp. Image © by Pete McGregor. Image licensed under Creative Commons Attribution-NonCommercial 4.0. .


Parasitoid wasps are potentially the most diverse group of organisms in the world (sorry beetle fans). They are abundant, they are crucial to the functioning of ecosystems, and they can be used by humans to control pests which damage food and other crops. Despite all this, they are incredibly understudied and there is still much that we don’t know about them on a global, regional, or even local scale. As with any species, the first step in collecting information on parasitoid wasps is to sample their diversity, in order to construct an inventory of species and to monitor how their diversity changes over time. The problem is:

  • How many samples should you take?
  • How many traps should you use?
  • How long should you leave the traps out for?
  • How much diversity can you expect to catch?
  • How many traps are required to achieve the level of diversity you want?



Netelia sp., a native New Zealand parasitoid wasp. Image © by Pete McGregor. Image licensed under Creative Commons Attribution-NonCommercial 4.0. .


By employing some of the concepts from optimal sampling theory, we can analyse the results from preliminary sampling and incorporate them into a new program that can tell us the answers to these questions. My master’s is tackling how this issue relates to New Zealand’s parasitoid wasps. I’ve collected my insect samples, and now I’m identifying the parasitoid wasps. Once that is complete, I’ll prepare some analyses which will help to build a foundation for the future study of these amazing insects.


Me setting up a malaise trap at the Oratia field site.


Once we know how to sample efficiently for parasitoid wasps, future work can look at some other interesting questions related to this group. For example, someone could look at how useful the NZ fauna would be as indicators of environmental quality, or surrogates for the diversity of other groups. This would help immensely in the selection of species and habitats to include in conservation planning. Who knows, you could be the one!



Tom Saunders is a Master’s student at the Centre for Biodiversity and Biosecurity, within the School of Biological Sciences, at The University of Auckland. He is supervised by Dr Darren Ward (Landcare Research). You can find out more about Tom and his research at