Lasiorhynchus barbicornis (Fabricius, 1775)

REDUCED NZ-Ento-Soc-Insect-Playing-Cards_Giraffe-Weevil

Common name: Giraffe weevil, tuwhaipapa

Order: Coleoptera      Family: Brentidae

 Size: 12 – 90 mm long

If you look carefully, during summer months these long, brown and stick-like beetles can be found aggregated on fallen trees in native forests across much of New Zealand. Males and females look remarkably different in appearance, so much so that they were originally described in 1775 as two different species. Giraffe weevils get their name due to the quirky long ‘snout’ (rostrum), which in males makes up about half of their body length and is used as a weapon to joust with other males. At the end of the rostrum are a pair of jaws (mandibles), and during battles males attempt to bite, push and throw their rival off the tree to secure sole access to a nearby female. After victory, males attempt to guard and mate with the female while she uses her rostrum to drill a tiny hole into the tree trunk. Once finished drilling she will turn around and lay an egg into the hole, and then plug it up with bark scraped from the surrounding area. Once hatched, larvae take at least two years to emerge from the tree, while the adult stage lasts only up to two months long.

Both the sexes are highly size variable, with females ranging from 12 – 50 mm in length, and males from 15 – 90 mm. The size difference between adult males should means that the tiniest males are unable to mate as often, as it would be unlikely that they could win fights against much larger rivals. However, males up to about 30 mm long are able to mate by sneaking in next to a female and mating with her under the ‘nose’ of a larger guarding male.


Resources:

Painting, C. J., Holwell, G. I. (2014) Observations on the ecology and behaviour of the New Zealand giraffe weevil (Lasiorhynchus barbicornis). New Zealand Journal of Zoology, 41: 147-153.

Painting, C. J., Buckley, T. R., Holwell, G. I. (2014) Male-biased sexual size dimorphism and sex ratio in the New Zealand giraffe weevil, Lasiorhynchus barbicornis (Fabricius 1775) (Coleoptera: Brentidae). Austral Entomology, 53: 317-327.

Painting, C. J., Holwell, G. I. (2014) Flexible alternative mating tactics by New Zealand giraffe weevils. Behavioral Ecology, 25: 1409-1416.

Painting, C. J. Holwell, G. I. (2014) Exaggerated rostra as weapons and the competitive assessment strategy of male giraffe weevils. Behavioral Ecology, 25: 1223 – 1232.