09 March 2015

Weta, rat, dog tucker

New Zealanders use the expression ‘dog tucker’ — literally, dog food — to describe something or someone about to meet disaster. For example, a professional rugby coach whose team loses eight straight games will inevitably be described as dog tucker — his sacking will be as certain as sunrise. Sadly, the term doesn’t just apply to rugby coaches, as I found out last night while prowling around the lower section of the No. 1 Line track, looking for interesting animals to photograph. Only a few minutes after entering the forest, I came across a beautiful, large, female weta — a flightless, nocturnal, grasshopper-like insect — sitting on the trunk of a tree at about head height. I photographed her and carried on up the track. Not long afterwards, I had an encounter that left me depressed, thinking this beautiful, ancient insect would inevitably end up as dog tucker.

Or, in this case, another type of tucker.

I’d heard something that sounded like the rasping of another weta but not quite right for that. I picked my way past the giant rimu and through a tangle of shrubbery, turning my head so the lamp played over the ground, along the fallen, rotting branches, and over the foliage. Nothing. Then I heard the sound again and turned towards it. A shadow moved, then two small orange-yellow eyes glowed back at me. I kept the headlamp trained on the eyes and switched it to full power. There, sitting on the fallen stipe of a tree fern frond, was Rattus rattus — the black, ship, or roof rat.

New Zealand has three species of rats, all introduced by humans. Kiore (Rattus exulans) are now rare on mainland New Zealand, and brown rats (Rattus norvegicus) tend to stay close to the ground, so they pose little risk to arboreal animals — my weta would probably be safe if she stayed up her tree. But black rats climb nimbly, as this one demonstrated when it finally ran off along a thin, flexible stem of supplejack and vanished into the night.

In New Zealand, the two pests with the highest public profiles are possums and stoats. While rats do get mentioned, in the public’s consciousness of conservation pests they rate less highly compared to possums and stoats, yet an infestation of Rattus rattus means disaster not only for the larger native insects like weta, ground beetles, and some of our spectacular weevils, but for birds too — the agile black rat easily raids nests, devouring eggs, chicks, and sometimes the adult birds who, particularly at night, can be sitting ducks (or in this case, fantails, riflemen, tomtits, and so on).

Rats also damage ecosystems by eating seeds. While some seeds need to be eaten so the plant can disperse, rats are not effective dispersers of larger seeds like those of tawa (a bit like an olive). Kereru, New Zealand’s native pigeon, swallow tawa fruits and crap the seeds out, often well away from the fruiting tree (Wotton & Kelly, 2012), but a tawa fruit is too big for a rat to swallow whole. Instead, the rat will do its usual ratty thing, nibbling away the flesh and either dropping the seed without dispersing it or gnawing the seed and therefore destroying it.

I could go on about the evils of rats, particularly black rats, but a more pressing point is what we should do about them. The good news is that possum and stoat control operations both kill rats. Rats eat and are killed by the poison baits used for possum control, and the traps used for stoat control also trap and kill rats. The bad news is that these control programmes don’t cover the whole country. They certainly don’t include the No. 1 Line track.

When I returned over an hour later, past the tree where I’d photographed the weta, she’d gone. I hoped she’d climbed higher into the canopy where she might be harder for a rat to find. The very fact she’d survived and grown to adulthood comforted me. Rats might have a relatively low status in the public consciousness compared to possums and stoats, but weta are ingrained in the national psyche — so much so that the company responsible for the remarkable special effects in Peter Jackson’s Lord of the Rings films named itself after these charismatic insects — and the thought that weta might become rare around here appalled me. More than that, though, I’d formed an attachment to this particular weta, who had been so cooperative, calmly sitting there while I photographed her. I hadn’t seen a big beautiful weta like this for a long time. She was the only one I saw last night (although I heard a couple more), and I couldn’t bear to think she was dog tucker.

Or, more accurately, rat tucker.

1. Strictly, 'weta' should have a macron over both vowels, thus: 'wētā'. The word without macrons has an entirely different meaning, but in practice you're unlikely to be misunderstood.

1. Last night's weta: Hemideina crassidens, the Wellington tree weta. The long thing that looks like a sting is her ovipositor—the apparatus she uses to deposit her eggs.
2. ... And this is last night's Rattus rattus. Note the very long tail and large ears, characteristics distinguishing it from the Brown rat, R. norvegicus. You can see a larger version of the photograph on The Ruins of the Moment.

Wotton, D. M., & Kelly, D. (2012). Do larger frugivores move seeds further? Body size, seed dispersal distance, and a case study of a large, sedentary pigeon. Journal of Biogeography, 39(11), 1973–1983. doi: 10.1111/jbi.12000

Photos and original text © 2015 Pete McGregor


Relatively Retiring said...

I hope your weta survived the night. Do black rats carry (and spread) as many diseases as their European relatives?

Ruahines said...

Kia ora Pete,
Very sad Pete. Though I greatly enjoy the thought of you walking silently in the bush listening to the weta..Top Maropea always has a few around. I recall one visit with my son Taylor and hearing him let out a shriek from the loo. A weta had fallen from the inside of the dunny roof onto his exposed lap. He didn't appreciate my laughter. They are very beautiful...only after I have come to know them.

Barbara Butler McCoy said...

I think my mind runs along the same thought train as RR's ... rats, plagues ... I try not to think of such things when I happen across rat traps behind commercial buildings around here. Shivers.

pohanginapete said...

RR, I don't know whether black rats are more or less effective carriers of disease than brown rats, but here, at least, the rat more commonly associated with human habitation seems to be the brown rat, with black rats perhaps relatively more common in the bush. That leads me to think the disease risk might be less for black rats.

Kia ora Robb. I imagine Taylor's visitor would have either hastened things along or ended all hope of success ;-) I'm afraid I'd have laughed too, though.

Barbara, rats in close proximity to humans are likely to carry far more diseases than those in the bush. Here in Aotearoa the main risk is from Leptospirosis, which ranges from something like a dose of the 'flu to a serious, even fatal, illness. As much as I appreciate rats as small, interesting mammals, I'd rather not have them around my place. Nor in the bush, for that matter.