Roadway massacre for billions of insects

‘And when white moths were on the wing, and moth-like stars were flickering out, I dropped the berry in a stream, And caught a little silver trout’

Moths could be seen, swirling like snow-flakes, in the headlight beams of cars during the 1950s. The windscreen of my father’s Ford Prefect was peppered with squashed bodies. There were still plenty of flying insects in 1997, the year when Mark Hostetler’s That Gunk on your Car: a unique Guide to the Insects of North America appeared. Not any more; Yeats’ white moths have all but flickered out. Only the occasional ‘daddy-long-legs’ crane-fly is likely to be caught in today’s wiper-blades.

“If the bee disappeared from the surface of the Earth,” said Albert Einstein, ‘Humans would have no more than four years to live.” Insects pollinate over 80% of flowering plants. Their disappearance is leading to ‘pollination deficiency’ worldwide. When the insects go, the amphibians reptiles and birds, which feed on them, soon follow.

The abuse of agricultural chemicals is mainly responsible for the disaster. Mono-cultural crop-planting adds to the problem. Expanses of oil seed rape, for example, offer a nectar-feeding bonanza to the local bees. Once the flowering stage has passed, however, the pollinators starve; they have no wild plants to support them. Diseases and parasites also take their toll. Now climate change looms.

There are more than a billion cars on the roads worldwide and the number will double by 2035. According to the Department of Transport, we have 2.5 million vehicles in
Ireland alone. So, to what extent is road transport implicated in the insect massacre?

The cars of my father’s day had flat windscreens, perpendicular the plane of the road and lethal to insects colliding with them. Vehicles nowadays, it’s argued, are more streamlined; insects are swept past the cars and fewer die.

Attempts have been made to determine the extent of the collision problem. Duane and Katherine McKenna collected the bodies of butterflies and moths along 13 road ‘transects’ in Illinois over a six week period in 2001. “The number of lepidoptera killed along roadways for the entire state of Illinois during one week was estimated at more than 20 million individuals,” they wrote. “The number of monarch butterflies killed may have exceeded 500,000 individuals. Our results suggest that increases in traffic rates and speed may, to a certain extent, increase mortality.”

Seven million Dutch vehicles cover about 200 trillion km each year. In 2011 Arnold van Vliet, of Wageningen University, asked 250 motorists to clean the front number plates of their cars, go for a drive and count the ‘splats’. The results suggest cars kill about 1,600 billion insects annually in Holland.

James Baxter-Gilbert, and colleagues from Laurentian University, measured insect mortality along a 2km stretch of motorway in Ontario, Canada. Their findings suggest that hundreds of thousands of insects are lost on that highway and that “hundreds of billions” die on North American roads each summer. More research, they say, is needed “to assess whether the mortality levels observed are contributing to the substantial declines of pollinating insects”.

How can the carnage be reduced? Allowing wild plants to flourish close to mono-cultural plantations provides sustenance to bees and other pollinators, on which the farmers’ livelihoods depend. Suburban gardeners might plant native trees and shrubs, incorporating some wild areas where insects can breed and their larvae can feed. Finally, we should use cars sparingly. Buses and trains kill insects but, per passenger-km travelled, they are far less lethal.

  • J. Baxter-Gilbert. Road mortality potentially responsible for billions of pollinating insect deaths annually. Journal of Insect Conservation. 2015.


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