Butterflies, Moths and Traffic!

[Pete Eeles]

I received the following note from a concerned HGV driver, and felt that he could do with the collective wisdom of UKBers. I'll be pointing him to this thread and truly appreciate the concerns expressed:

Dear Sir,

I am a HGV driver and I have particular concerns over the plight of bees and butterflies. I wish to draw your attention on a possible factor on the decline.

When I am driving on the country's roads and motorways during warm weather it is inevitable that insects are struck. In a typical day several bees and butterflies are hit and I feel personal guilt. I would guess that if a truck speed is about 20 to 25 mph the insect would bounce off but with increasing speed and the angle of strike the damage done to the insect would be obvious. If we were to assume the average number (5 to 10) of such casualties per day and multiply it by the number of vans and trucks on the roads then the figures are staggering.

What is the solution? Most of the time it is not at all possible to avoid hitting the bees and butterflies but from my opinion I can only suggest windscreens that somehow deter the insects flying into them or avoid them. Secondly there may be something that can be installed along the side of roads and motorways that would deter the insects from roaming into the carriageways.

Thank you for your time.

My own thoughts are that any losses will be minuscule when compared with habitat loss and there is no need, therefore, to be concerned. Thoughts? And thanks in advance!

Cheers,

- Pete

[Padfield]

It's very good to know professional road-users are concerned about such things.

From a purely conservation point of view, I am certain there is nothing to worry about. I have watched butterflies in Spain beside roads with very heavy use and the number killed is very small compared to the number flying. Motorway margins are far more vibrant butterfly habitats than pesticide-ridden arable land. I would interpret the frequency of hits more as a measure of the richness of the habitat than a threat to the butterflies. Common species will much more commonly be hit; rare species will very rarely be hit.

From the point of view of individual butterflies, I would suspect that the more aerodynamic a vehicle is, the more any insects will be streamed over its surface with minimal percussion. If a vehicle experiences less opposing force from wind resistance, then the air mass, by Newton's third law, is experiencing less force from the vehicle. Any insects within the air mass will experience less force too. I would therefore suggest the best way to minimise insect damage is to maximise the aerodynamic profile of the vehicle (without also increasing the speed, of course). This would have economic benefits too...

Guy

[David M]

Must admit, I've only ever knowingly killed one butterfly whilst driving - a Green Veined White that somehow became tangled in my windscreen wiper. What's more, I don't ever recall seeing any dead butterflies alongside roads in the UK. On the continent, I've seen many roadside casualties but this may be due to butterflies' propensity to bask on the roads in warmer climes to take advantage of the heat therein rather than any collisions in flight.

HGVs are quite 'square' compared to cars and vans though, so maybe this is a contributory factor.

Make HGVs more aerodynamic and the problem should reduce, but I doubt any manufacturers will have this in mind when drawing up their design blueprints!

[bugboy]

I would hazard a guess that due to butterflies large wing area/small body ratio they are far more likely to be swept around in the slipsteam of a fast moving vehicle rather than suffer a fatal headon collision. Heavier bodied insects such as beetles, flies and bees have probably a higher 'hit' ratio. To use an analogy, imagine a butterfly is a piece of tissue paper and a beetle is a small pebble.

On holiday in Slovenia about 12 years ago, we were walking along a country road on a particularly hot day and whenever there was a break in the roadside canopy allowing the sun through, we found several dead butterflies littered on the tarmac. My assumption at the time was that they were caught out from heat stress: the surface of the road was almost too hot to touch and I presumed as they flew across, they hit a wall of extreme heat which knocked them out, causing them to fall onto the road and then basically get cooked .

[Scott Barron]

Hi all,

Pete, you may remember I emailed you a year or so back about a Continental Swallowtail I found as a road casualty.

This is a subject I have a little personal experience with, so I hope my views and opinions maybe of interest. I have a specimen collection (don't jump to conclusions let me explain) that I have built up over about 25 years. It is made up entirely from insects that have been killed by cars, which I have collected from roadsides local to me in West Cornwall. I must stress that NOT ONE INSECT IN MY COLLECTION HAVE I KILLED MYSELF THEY ARE ALL TRAFFIC CASUALTIES.

My method for collecting is basically that I go out on my push bike and pick up insects from the roads that have been hit and killed by cars. I would not like to hazard a guess regarding the numbers of butterflies and moths involved but it must be tens of thousands (this being on only a few roads local to me). In my opinion the air flow or size, shape, or wing size of the insect does not matter, if it is on collision course with a car it will come out second best and end up more often than not dead (I have managed to rescue and release a few individuals back into the wild). Of course habit loss is a major factor in population decline, but again in my opinion the impact of the metal beast most if us drive about in every day cannot be ignored and must be having an impact on numbers nationwide.

I hope my views and experiences are of interest.

Scott.

[Jack Harrison]

I know I am always coming up with hypotheses but this one is an old one that I raised some years ago.

I have read that Black-veined Whites – which fly slowly - are killed in enormous numbers on some roads in France. Now the BV White was never common in England but its final extinction coincided with a massive increase in road traffic in the early years of the 20th century. Was the car the final straw?

My most bizarre butterfly sighting from a car was when waiting at traffic lights opposite Tesco in Hatfield. An unmistakeable Green Hairstreak fluttered over the Tesco shrubbery. I diverted, used the Tesco car park but had no more sightings.

Jack