The larval weevils tunnel into wood for at least two years before emerging, and live for only a few weeks as adults.

[2] Mitochondrial DNA suggests that during the Pleistocene ice ages giraffe weevils were only found in the remnant forests of Northland, and have expanded southward during this current interglacial.

[3] 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.

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.

[1] The beetle's Māori names include pepeke nguturoa ("long-beaked beetle": ngutu roa is another name for kiwi),[7] 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.

[10] 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.

[8] Giraffe weevils are mostly active by day, sheltering in the canopy at night, and feed on sap.

[12] When suddenly disturbed, they will drop backwards off a tree trunk and lie in the leaf litter, playing dead, for up to an hour.

[12] The life cycle of Lasiorhynchus barbicornis starts when a female lays a single egg about 3–4 mm deep into a tree.

Some of these tree species include kauri (Agathis australis), lacebark (Hoheria spp.

[8] The female bores a narrow hole with her mandibles into the trunk, pulling her head out every half-millimeter to clear away sawdust.

[12] Dissections of larvae show they feed on fungus growing in the larval tunnels, not the wood itself.

[14] During the pupal stage, the weevil's rostrum is doubled underneath the body, but it straightens when the adult beetle emerges and eats its way out of the tree, leaving a square tunnel.

The female has a specialized rostrum and mandibles which allow her to collect debris while drilling into the bark and push it out from the tree.

According to studies conducted by New Zealand entomologist Rebecca J. LeGrice, 65% of male L. barbicornis were able to mate several times in the span of just one hour.

[18] On average, it has been observed that male Lasiorhynchus barbicornis, when given the option, opt to mate with larger females.

In this circumstance, males will use their mandibles which curve downward and their long rostra to rake across the pair in an attempt to separate the couple and disrupt mating.

Many male L. barbicornis have missing legs, especially tibia or tarsa, which is often a result of male-male mating conflicts.

The snouts, called rostra, of male New Zealand giraffe weevils also grow proportionally to their body size.

[22] Additionally, larger individuals invest about 60% less metabolic active tissue and energy into their rostra compared to the smallest males.

This is indicative of a special metabolic cost saving mechanism that is unique to the physiology of large male L.

[13] L. barbicornis exhibit slow, non-directional flight patterns and are often unable to avoid large objects.

[13] It is thought that increased investments in wing and leg length in male L. barbicornis compensates for their poor flying abilities.

[9] According to studies conducted by Dr. Christina J. Painting for the Biological Journal of the Linnean Society, Lasiorhynchus barbicornis likely had a restricted habitat range during the Pleistocene era which was followed by a glacial retreat.

In contrast, the southern population lives in the more warm wet lowland forests of the western South Island.