Of the 60,000 or so species of Trachelophorus giraffa stands out by, well, a neck’s length. It is one of the iconic and endemic ‘must-see’ species for those planning a visit to the island of Madagascar.
The giraffe-necked weevil is relatively small at 25mm at full stretch, but its bright, berry-red wing cases, which contrast with the black, lustrous body, make it ‘pop’ against the lush foliage of its eastern Madagascan forest home. It is the weevil’s extraordinary anatomy, though, that makes it a must-see for visitors.
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These weevils, like so many creatures on this group of islands off the southeastern coast of Africa, are found nowhere else on the planet. As is often the case in the natural world, when something appears bizarre, it frequently has a compelling story behind it. It is undoubtedly the ‘neck’ that generates the most questions.
The male has the most spectacular and lengthy neck, comprising two extremely elongated segments immediately behind the head, giving it the profile of a small JCB.
But to the biologist, the question is, what is its purpose? Why the long neck? It took me quite a bit of time and patience to witness the neck in action. Weevil watching is made more challenging by the extreme sensitivity of these insects to disturbance.
Just a careless brush against the foliage or a knock on a branch – sometimes you need only look at a weevil in a funny way – and they either pull in their.legs and drop off, to be lost in the weeds, or they achieve what looks like a mechanical impossibility and fly off.
Eventually, though, several weevils later, two males were found together, using a leaf of what is often referred to as the giraffe-necked weevil tree’, Dichaetanthera cordifolia, as a wrestling ring. Each male uses its neck to push, lean, flip and shove its opponent, a scene not dissimilar to a couple of stags battling it out during the rut.
And, just like the deer, they have an audience. The shorter-necked females look on, and it seems that the neck is a means by which the males compete for their attention and, therefore, mating rights. But what about the females? They might have a neck that is two or three times shorter than that of the males, but they still have a longer-than-average front-end extension compared with most other weevils.
They also have another feature that is rarely mentioned: really chunky thighs.
The females may not be as iconic as the males, but they are arguably even more fascinating. Once they’ve mated with their chosen partner, they set about the highly labour-intensive process of laying an egg – one of the reasons they’re found on a specific species of tree. Here, the female creates a parcel from one of the leaves.
She accomplishes this through a complex procedure of biting along the veins, creating scored lines that makes it easier to fold. She then straddles the centre vein of the leaf lengthwise and, using her powerful legs, squeezes the two sides of the leaf together. She folds the leaf in from its ends, pushing, pulling and tucking the folds into place. This is where her neck comes in handy: it acts as a stout lever and bradawl in one, and she employs it to slowly construct a cell for her egg, with the previously bitten holes interlocking like Velcro.
It is a sewing project of great complexity and beauty. She does all the work at this stage, with the males strutting around, guarding her from other males and perhaps predators and parasites. When she’s finished, she lays a single egg inside the leaf package before a final snip sends the whole thing falling to the forest floor.
Once the solitary weevil grub, safely contained inside a sort of live-inburrito, has hatched from the egg, it spends the first days of its life feeding on the walls of its nursery. A wonder weevil indeed
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