I couldn’t not use this – it is (sadly) one of my favourite films 😊
Anyone who has driven (or walked) along a road will have come across roadkill, be it squirrels, pheasants, badgers, deer or even something more exotic, perhaps it us only us entomologists who notice the squashed invertebrates ☹
Dead carabids and mayflies Shay Lane, Staffordshire, 8th June 2021
But, lets leave the roadkill for a moment, and in the spirit of the title of the film, start in the air. The first thing I discovered when I started to search for the effects of aircraft on insects is the paucity of literature on the subject – it turns out that people are much more interested in stopping disease carrying insects being transported by air or, and coming as a bit of a surprise to me, stopping insects causing plane crashes (House et al., 2020; Grout & Russell, 2021). The aircraft industry is so concerned about the physical dangers posed to ‘planes by insects that NASA actually have a Bug Team dedicated to developing insect proof aircraft.
I am, however, more concerned about how dangerous aircraft are to insects. First, we need to know how many insects are up there and what the probability of them being struck and killed by aircraft is. I’m guessing that bug strike is pretty common, otherwise NASA wouldn’t have a Bug Team. The majority of insects in the air are found at 300-600 m, although this does vary in relation to time of day (Reynolds et al., 2005). Getting a figure for the actual number of insects in the air is as you might expect, actually quite difficult. The first attempt to trap and collect insects using an aircraft was in 1926 in Louisiana (USA) using a specially designed trap (Glick, 1939). These do not seem to have been particularly effective as 5 years of trapping, involving 1528 hours of flying, caught just under 30 000 insects (Glick, 1939). Those of us who have operated pitfall traps for any length of time would consider this a very modest haul 😊
Glick (1939) The aircraft insect trap
That said, the exercise was obviously more hazardous than even collecting insects from roundabouts as this very laconic extract highlights:
“The skill of the pilots who flew the collecting airplanes is evidenced by the fact that no fatalities occurred. Only one major accident occurred, when a forced landing resulted in the destruction of the craft and injury to both the pilot (McGinley) and the writer. Such mishaps must be expected in a more or less hazardous undertaking.”
The distribution of catch number was very similar to that reported from the more recent UK study using radar (Reynolds et al., 2005) and is reinforced by this statement from the NASA Bug Team; “The reason we do these tests at low altitudes or do a lot of takeoffs and landings is because bug accumulation occurs at anywhere from the ground to less than 1,000 feet,” said Mia Siochi, a materials researcher at NASA Langley”.
Given the number of flights made globally and the investment being made into protecting aircraft from bug strike, I would assume that the number of insects being killed by aircraft worldwide is probably very high. I am sure that someone with the skill, time and inclination, can probably come up with a fairly realistic figure. Over to you Dear Readers.
Next up, if we keep to the film title, are trains. There has been a bit more work looking at the damage that trains do to insects, not a lot, but something is better than nothing. Work collecting train kill from railway lines showed that snails were particularly vulnerable to being run over, similar to the effects on trail-following ermine moth caterpillars that I observed in Finland in 1981, with Ephemeroptera (Mayflies) in second place (Pop et al., 2020). This, as the authors suggest, was almost certainly due to the time of year and the presence of a lake nearby. Unfortunately no one has done the equivalent of a train splatometer which might be rewarding as these observations from correspondence in British Birds magazine suggest that locomotive engines are causing some mortality to flying insects. Over to you Bug Life. How about getting the train companies to fit splatometers?
Finally, cars and their effect on insect life. There is anecdotal evidence out there, after all as drivers we have all seen moths in our headlights at night and used our windscreen washers and wipers to try and remove dried on insect corpses and their haemolymph from our front windscreens.
My front bumper – sadly (or perhaps not) much less insect spattered than in the past
Yes, anecdotally we know that insects are being hit by cars (see above) and on my front number plate, a couple of weeks ago (beginning of June) I counted 73 insects, mainly aphids after a 245 km trip. The problem as I see it, is quantifying the numbers killed and calculating the effect that this has on insect abundance. I have mentioned the splatometer in an earlier post which attempts to standardise the number plate counts and I am pleased to see that this has now been revived by Bug Life, and will hopefully carry on for many years. The idea behind this is that over the years we will be able to see if insect numbers as reflected by the change in numbers of splats are increasing, decreasing of remaining the same. This will not, certainly as described, tell us how many insects are being killed by road using vehicles, although it would be possible if the data were collected over delineated stretches of road (Baxter-Gilbert et al., 2015). It is not just flying insects that are killed by cars; not all flying insects fly across roads, many seem happy to walk to the other side, reckless as that may seem.
A brave, or possibly fool-hardy carabid beetle crossing the road – Guild Lane, Sutton, Staffordshire, 9th June 2021.
There have been enough studies done looking at the interactions between roads and insects for a review article to have been published fairly recently, although not all the papers deal directly with mortality effects (Munõz et al., 2015). Many studies have recorded the species affected and the number of dead individuals found but few have attempted to calculate what this means in total. Most studies, as we might expect, have been on large, easily identifiable charismatic species (Munõz et al., 2015) and it from these that we do have some idea of the magnitude of the mayhem caused by road traffic. Some of the figures are incredibly high. A survey of Odonata road kill, albeit near a wetland, of two 500 m stretches of dual carriageway in the Great Lakes region of the USA revealed that at least 88/km/day were being hit and killed by vehicles (Riffell, 1969). Another study in the USA, this time on Lepidoptera, calculated that about 20 000 000 butterflies (mainly Pieridae) were killed in one week in September (McKenna et al., 2001). The most dramatic figures however, are those from a study in Canada which estimated that 187 billion pollinators (mainly Hymenoptera) are killed over the summer in North America (Baxter-Gilbert et al., 2015). An unpublished study by Roger Morris (thank you Richard Wilson @ecology_digest for bringing this to my attention) also highlights the dangerous effects of cars on Hymenoptera). Despite the mounting evidence of the harm that road traffic does to insects there is remarkably little information about how this can be reduced, although I did find a paper that noted that if insects are struck by cars driving at speeds of 30-40 km/h they survive the crash whereas speeds greater than this prove fatal (Rao & Girish, 2007). It might be possible to impose insect safe speed limits along stretches of road that go through sites of special insect interest (perhaps I should try and coin that acronym, SSII, as an additional/alternative term to SSSI (Sites of Special Scientific Interest), but I am not sure how amenable drivers would be to signs telling them to slow down because of insects😊, considering how few drivers slow down in response to the signs warning them about deer and other vertebrate hazards. Another option would be to design road vehicles so that the air flow across them pushes insects away rather than into them; this may already be fortuitously happening as Manu Saunders points in her interesting post about the ‘windscreen anecdote’. That said, even if cars are more aerodynamic and less likely to splatter insects, the levels of road kill reported in the papers I have cited earlier, still imply that insects are being killed by traffic in huge numbers.
This one didn’t get stuck on a car, but died just the same – A519 outside Forton, Staffordshire, 15th June 2021
Even if we do accept that deaths down to direct impact with vehicles is lower than in the past, the roads on which we drive our cars are also having a negative effect on insect numbers. Roads, particularly those surfaced with tarmacadam, present an inhospitable surface to some insects which may make them reluctant to fly or walk across. It has been shown that bee and was communities can be different on different sides of a road (Andersson et al., 2017) as the road act as barriers, particularly for smaller species of bees (Fitch & Vaidya, 2021).
Despite the mortality that vehicles impose on insects, roads are not necessarily a totally bad thing for invertebrates; road verges, when sympathetically managed, can provide overwintering sites for a range of arthropod species (Saarinen et al., 2005; Schaffers et al., 2012) and some insect species seem to enjoy feeding on roadside vegetation because of the increased nitrogen content of the plants living alongside traffic (Jones & Leather, 2012).
Overall however, given the very high mortality rates directly associated with cars and other road traffic and the very real indirect effects caused by habitat fragmentation, it would seem that we have much to do to make roads safer for insects and other animals.
Andersson, P., Koffman, A., Sjödin, N.E. & Johansson, V. (2017) Roads may act as barriers to flying insects: species composition if bees and wasps differs on two sides of a large highway. Nature Conservation, 18, 41-59.
Baxter-Gilbert, J.H., Riley, J.L., Neufeld, C.J.H., Litzgus, J.D., & Lesbarreres, D. (2015) Road mortality potentially responsible for billions of pollinating insect deaths annually. Journal of Insect Conservation, 19, 1029-1035.
Fitch, G. & Vaidya, C. (2021) Roads pose a significant barrier to bee movement, mediated by road size, traffic and bee identity. Journal of Applied Ecology, 58,1177–1186.
Glick, P.A. (1939) The Distribution of Insects, Spiders, and Mites in the air. Technical Bulletin no. 673, USDA. https://naldc.nal.usda.gov/download/CAT86200667/PDF
Grout, A. & Russell, R.C. (2021)H Aircraft disinsection: what is the usefulness as a public health measure? Journal of Travel Medicine, 28, taaa124.
House, A.P.N., Ring, J.G., Hill, M.J. & Shaw, P.P. (2020) Insects and aviation safety: The case of the keyhole wasp Pachodynerus nasidens (Hymenoptera: Vespidae) in Australia. Transportation Research Interdisciplinary Perspectives, 4, 100096.
McKenna, D.D., McKenna, K., Malcolm, S.B. & Berenbaum, M.R. (2001) Mortality of lepidoptera along roadways in Central Illinois. Journal of the Lepidopterist’s Society, 55, 63-68.
Melis, C., Olsen, C.B., Hyllvang, M., Gobbi, M., Stokke, B.G., & Røskaft, E. (2010) The effect of traffic intensity on ground beetle (Coleoptera: Carabidae) assemblages in central Sweden. Journal of Insect Conservation, 14, 159-168.
Munõz, P.T., Torres, F.P. & Megias, A.G. (2015) Effect of roads on insects: a review. Biodiversity & Conservation, 24, 659-682.
Pop, D.R., Maier, A.R.M., Cadar, A.M., Cicort-Lucaciu, A.S., Ferenți, S. & Cupșa, D. (2020) Slower than the trains! Railway mortality impacts especially snails on a railway in the Apuseni Mountains, Romania. Annales Zoologici Fennici, 57, 225-235.
Reynolds, D.R., Chapman, J.W., Edwards, A.S., Smith, A.D., Wood, C. R., Barlow, J. F. and Woiwod, I.P. (2005) Radar studies of the vertical distribution of insects migrating over southern Britain: the influence of temperature inversions on nocturnal layer concentrations. Bulletin of Entomological Research, 95, 259-274.