Having a flutter: a lack of food for butterfly larvae has eaten into numbers. Photo: Getty
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Butterflies are beautiful but we need to love their larvae too

The numbers of monarch butterflies are at a record low and a large part of this is because of the disappearance of the milkweed plant, eaten by caterpillars.

Sometimes, to prove a point, you have to starve a larva. It’s all too easy to be bewitched by the beauty of a passing butterfly but not so easy to admire the foraging of a voracious caterpillar. We should, though: it turns out that the two are linked.

Researchers in the US have been putting monarch butterfly larvae on strict diets and observing the consequences for the butterflies they become. This kind of butterfly is in grave trouble. Every year, the insects perform an extraordinary 3,000-mile migration from Canada and the northern US down to central Mexico, where they gather on a few mountaintops for the winter.

In 2012, about 60 million monarchs arrived in the Mexican mountains. That was a record low until the 2013 figures came in – the number arriving was almost half that of the previous year. It was the lowest figure since records began in 1993.

A big problem is the widespread disappearance of the milkweed plant. Monarch larvae eat only milkweed and urbanisation and industrial farming practices have made it scarce.

Hence the research, which was published last April. The researchers found that restricting the monarch larva’s milkweed intake reduces the size of its wings when it emerges from the chrysalis. It is likely that this stunted growth makes the migration much harder work.

Monarchs also seem to need food to maintain their looks. The colours of the orange-and-black wing patterns are deeper, with more striking contrast, in monarchs covering the most distance. It may be that feeding up the larvae to produce better fliers will also produce more beautiful butterflies.

The aesthetic argument is one of very few available to conservationists. Researchers can’t point to any specific benefit that monarchs bring: they don’t seem to play a crucial role in any ecosystem and their removal from specific ecosystems “would probably not have lasting repercussions”, as one report put it. The monarchs don’t contribute anything apart from a beautiful spectacle when they migrate.

British butterflies are even worse off – they don’t have a spectacular migration. In March, the UK government issued a draft of its “pollinator strategy” document, which outlines what might be done about the severe decline in numbers of pollinating insects such as bees, butterflies and moths. The charity Butterfly Conservation said that it “strongly welcomes” the proposed strategy (though it dismisses as “ludicrous” the idea that pesticide companies should self-regulate).

Yet there is a slightly dejected tone to the charity’s chief executive’s observations. He points out that while bees are acknowledged to have economic value as pollinators of agricultural crops, butterflies are not and are therefore less likely to receive government help. In the age of market forces, it is not enough to be beautiful.

However, as the Intergovernmental Panel on Climate Change noted in March, butterflies’ relatively short life cycle and “high dispersal capacity” make them very useful markers of climate change.

That is certainly true of the British butterfly population, which, apart from a few cold-loving species, is thriving in our warming climate. In the past 20 years, for instance, the orange-and-black comma butterfly has spread 137 miles northwards.

If you lived in Edinburgh in the early 1990s, you would not have seen one. Now they’re not an uncommon sight: an effect of global warming that’s hard to complain about.

Michael Brooks holds a PhD in quantum physics. He writes a weekly science column for the New Statesman, and his most recent book is At the Edge of Uncertainty: 11 Discoveries Taking Science by Surprise.

This article first appeared in the 14 April 2014 issue of the New Statesman, Easter Double

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“Minoan pendant”: a new poem by Mark Granier

“Yes – I press my nose / to the pleasantly warm glass – / it’s a copy of one I saw / cased in the cool museum”

Yes – I press my nose
to the pleasantly warm glass –
it’s a copy of one I saw
cased in the cool museum –
gold beaten to honey, a grainy
oval dollop, flanked by two
slim symmetrical bees –

garland for a civilisation’s
rise and collapse, eye-dropped
five thousand years: a flash
of evening sun on a windscreen
or wing mirror – Heraklion’s
scooter-life buzzing and humming –

as I step in to browse, become
mesmerised by the warm
dark eyes of the woman
who gives her spiel and moves
softly and with such grace,
that, after leaving, I hesitate

a moment on the pavement
then re-enter with a question
I know not to ask, but ask
anyway, to hear her voice
soften even more as she smiles
and shakes her hair – no.

Mark Granier is an Irish poet and photographer. He is the author of four collections of poetry, most recently Haunt (Salmon).

This article first appeared in the 16 June 2016 issue of the New Statesman, Britain on the brink