The New Zealand giraffe weevil, Lasiorhynchus barbicornis, is a distinctive straight-snouted weevil in the subfamily Brentinae, endemic to New Zealand. L. barbicornis is New Zealand's longest beetle, and shows extreme sexual dimorphism: males measure up to 90 mm, and females 50 mm, although there is an extreme range of body sizes in both sexes. In males the elongated snout (or rostrum) can be nearly as long as the body. Male giraffe weevils use this long rostrum to battle over females, although small males can avoid conflict and 'sneak' in to mate with females, sometimes under the noses of large males. The larval weevils tunnel into wood for at least two years before emerging, and live for only a few weeks as adults.
Taxonomy
This species was described by the Danish entomologist Johan Christian Fabricius in 1775, from specimens collected by Joseph Banks in 1769 on Cook's first voyage to New Zealand, presumably from Ship Cove in Queen Charlotte Sound. Fabricius described the smaller females as a different species, Curculio assimilis, but suspected they were the males of what he named Curculio barbicornis (later moved to its own genus, Lasiorhynchus). His specimens are now in the Banks Collection of the Natural History Museum, London, and the Fabricius Collection in the Natural History Museum of Denmark.
L. barbicornis is occasionally accused of not being a weevil at all, but it fact it is in the family Brentidae, the straight-snouted weevils, as opposed to the much larger family Curculionidae or "true" weevils; brentids lack the distinctive geniculate (elbowed) antennae that characterise curculionid weevils. These and several other families are part of the superfamily of all weevils, Curculionoidea. L. barbicornis is the only member of the Brentinae (a tropical subfamily) in New Zealand, and its closest relatives are in Sulawesi, Australia, Vanuatu, and Fiji. It is the only member of the genus Lasiorhynchus.
Etymology
Lasiorhynchus means "densely hairy rostrum"; barbicornis ("bearded horn") refers to the dense black backward-directed beard underneath the male's rostrum, or possibly to its hairy antennae. The beetle's Māori names include pepeke nguturoa ("long-beaked beetle": ngutu roa is another name for kiwi), tūwhaipapa, and tūwhaitara, the latter two after the Māori god of newly made canoes, because its canoe-like body and upturned rostrum resemble a waka and prow.
Description
Giraffe weevils have a distinctive elongated head, and reddish-brown markings on their elytra. They are the only weevils in the world with a visible scutellum.
They are New Zealand's longest native beetle, and have been identified as the longest brentid weevil in the world by researchers Christina. J. Painting and Gregory I. Holwell. They vary enormously in size, from 15 to 90 mm total length in males and 12–50 mm in females. This wide variation in body size, particularly in the length of the male rostrum, may be in response to changing environmental conditions from year to year. Body size increases the further south the weevils live, but male rostra get proportionately less long with increasing latitude.
These weevils display extreme sexual dimorphism; males have an elongated rostrum or snout with antennae at the tip, which they use as a weapon for fighting over females. The female giraffe weevil has a shorter rostrum with antennae about halfway along, which allows her to bite egg-laying holes in tree trunks without damaging her antennae.
Giraffe weevils are mostly active by day, sheltering in the canopy at night, and feed on sap. When suddenly disturbed, they will drop backwards off a tree trunk and lie in the leaf litter, playing dead, for up to an hour.
Life cycle
Eggs are laid on dying wood from October to March. The female bores a narrow hole with her mandibles into the trunk, pulling her head out every half-millimetre to clear away sawdust. During this time the male mates with and guards her, and helps her disengage with the hole if she gets stuck. The hole is usually 0.5 mm wide, 3–4 mm deep, and at a 45° angle to the trunk of the tree. When finished, she lays a single egg in the hole, which is then refilled with sawdust and hidden with bark fragments. The whole process takes around 30 minutes.