A Mighty Rostrum in New Zealand - Observation of the Week, 2/22/20

Our Observation of the Week is this male New Zealand Giraffe Weevil, seen in New Zealand by @lisa_bennett!

Like Babe Ruth, Lisa Bennett called her shot on February 11th. “Every summer I have been keeping an eye out for [New Zealand giraffe weevils], but so far I hadn’t seen any,” she tells me. “[And] I did mention to my husband in the morning that maybe today would be the day!” 

Imagine my delight when I saw this one on the very tree we were picnicking under! My oldest son happily held it for the photo, and gently put it back on the trunk of the tree afterwards. We also saw many stick insects that day, as well as freshwater crayfish, cicadas, birds and even a gecko skin. I love seeing the fascinated look on their faces when we find things, and I love that they learn to be respectful and gentle, and to return them to their home if they have been handled.

The longest species in the Brentidae, or straight-snouted weevil family, the New Zealand giraffe weevil is highly sexually dimorphic, with adult males reaching up to about 90mm in length and adult females about 50mm in length - the main difference being the exaggerated length of the male’s rostrum. After emerging as adults in the summer, females drill holes in the wood of dead or dying trees, where they will eventually lay a single egg, and “during this time males will compete fiercely for access to females for copulation, using their greatly elongated rostrum and enlarged mandibles to push, bite, pull and grapple other males from the female, occasionally throwing their opponent off the tree.” (Painting and Holwell, 2013) Interestingly, larvae eat fungi which grow in their burrow, not the wood itself.

Lisa says she “was especially animal-obsessed as a kid,” and in addition to nature books she collected nests, shells, and other natural emphera. “My parents didn’t really understand my interest but they encouraged it,” she remembers, “which I’ll always be grateful for, although my father drew the line at pet frogs singing in my bedroom!” A stay-at-home mom, she enjoys introducing her sons to the flora and fauna around their abode. “My eldest son especially enjoys finding ‘species’,” she says. “It blows my mind that we find a species new to us almost every time we go exploring.”

For years Lisa (above, with her sons) has been trying to record the biodiversity of their 13 acre property but says “my spreadsheets weren’t cutting it” and it was difficult to find identification resources. iNaturalist has been a boon in both of those areas, and she tells me “to have such a wonderful way of recording all the data and having such expert knowledge just a click away is amazing!...

I love the way it has made me notice so much more that I ever did before, and I feel when I visit a place now I understand it, biologically at least, much more than I ever did before. I wish it had been around 30 years ago! I’m making up for lost time now though! :)

- by Tony Iwane

- smaller males will sometime sneak in and mate with a female, as this really informative video shows.

- female New Zealand giraffe weevils have much shorter rostra.

- this is not the first giraffe weevil Observation of the Week! Back in 2016, we featured @nlblock’s observation of a giraffe weevil in Madagascar!

Posted on February 23, 2020 05:37 AM by tiwane