Global warming is apparently leading to glow-worm waning in the UK. Today the Guardian has an articlei on its website under the title “How the speed of climate change is unbalancing the insect world”. This deals with a lot of issues, and inevitably it’s always bad news. Good insects are going to struggle with climate change, while nasty ones are going to thrive. It’s always the way, isn’t it? However, one section, which particularly interests me, concentrates on glow-worms in the UK. And this is what it solemnly tells us:
Further south, in the UK, glowworm numbers have collapsed by three-quarters since 2001, research has found, with the climate crisis considered the primary culprit. The larvae of the insects feed on snails that thrive in damp conditions, but a string of hot and dry summers has left the glowworms critically short of prey.
No link is offered up to support the claim that climate change is the primary culprit for the decline in UK glow-worm numbers, though a team of researchers from Sweden and Spain are mentioned (though not, curiously, researchers from the UK).
But here’s the thing. On 22nd February 2020, the Guardian ran a story under the headline “Why the lights are going out for fireflies”ii. And it told a rather different story. It started by discussing declining firefly populations in the US, then went on to say that the best data is from the UK, where citizen scientists have tracked the UK’s only firefly, the common glow-worm, Lampyris noctiluca, since the 1970s.
Then it linked to a reportiii entitled “A Global Perspective on Firefly Extinction Threats” which, as even the Guardian had to acknowledge, makes it abundantly clear that climate change is far from being the main threat to glow-worms. Indeed, as the report’s abstract states:
We conducted a survey of experts from diverse geographic regions to identify the most prominent perceived threats to firefly population and species persistence. Habitat loss, light pollution, and pesticide use were regarded as the most serious threats…
And the body of the report goes further:
More than half of the 49 respondents assigned the highest possible threat score (5) to habitat loss, whereas nearly one-third did so for light pollution, and one-fifth did so for pesticide use. However, their threat scores differed considerably across geographic regions… with additional threats such as water pollution and tourism ranked as important concerns in some regions.
Rather than quote extensively from the report, I simply note that habitat loss was noted as occurring for a variety of reasons, though other than two brief references to drought, the reasons are all man-made, but nothing to do with climate change. In Europe, reference is made to urbanization, industrialization, and agricultural intensification, plus increased use of pesticides, herbicides, and fertilizer. In England specifically, mention is made of road construction, ditch filling, timber stockpiling (and drought; I’m nothing if not fair). Italy sees blame put on agricultural intensification, while in Spain it’s down to the abandonment of small orchards and irrigated agricultural plots in which Nyctophila reichii, Lampyris iberica, and Lamprohiza paulinoi often occur. Once abandoned, these cultivated areas become more xeric and less suitable for snails, which constitute the main prey for certain fireflies, apparently. In Malaysia it’s conversion of riverbank mangroves to agriculture, aquaculture, and urbanization. Throughout south east Asia, large areas of riverbank mangroves have been cleared for oil palm plantations, shrimp farms, or flood mitigation, making these sections unsuitable for the growth and development of Pteroptyx firefly larvae and their snail prey
On and on it goes. Globally, increasing human populations along coastlines have caused extensive habitat loss and fragmentation, threatening both mangrove fireflies and other species inhabiting coastal marshes. In the western United States and Texas, several fireflies are restricted to habitats adjoining permanent water sources, including rivers, streams, lakes, ponds, springs, and irrigated fields. Groundwater pumping to meet urban and agricultural water demands has substantially reduced surface water flow and lowered groundwater tables, and this might be exacerbated by climate-change induced drought (though that’s far from being the primary issue).
Apart from habitat loss, light pollution, and pesticides, other threats were mentioned – water pollution, tourism, overharvesting, invasive species, and finally climate change. And what do the authors have to say about climate change?
…the effect of anthropogenic climate disruption on firefly populations remains unknown, the restricted ranges and specialized habitat requirements of certain fireflies suggest that they are likely to be threatened by drought and sea level rise.
In other words, it’s a potential threat, and an additional problem, but it’s well down the list, and certainly isn’t, as today’s Guardian article tells us, “the primary culprit”.
And yet, despite all that, less than two weeks after the Guardian article summarising the report that said climate change was almost immaterial, on 5th March 2020 a new articleiv appeared at the Guardian under the heading “Glowing, glowing, gone: plunge in glow-worm numbers revealed – Exclusive: study shows a 75% fall in 18 years in England, with climate a clear factor”. The story this time was broadly the same as the story today:
Glow-worm numbers have plunged by three-quarters since 2001, research in England has revealed, with the climate crisis a clear factor.
The larvae feed on damp-loving snails, and increasingly hot and dry summers mean fewer prey and a greater risk of glow-worms becoming desiccated.
So, which is it? Climate change or not climate change? Well, there’s a problem with blaming hot, dry summers, at least so far as the data provided by the Met Office makes clear. They supply a UK summer rain chartv among other things, and I can’t see the decline in summer rainfall postulated by the Guardian. In fact, since the collapse in numbers is specifically said to have occurred sine 2001, on the contrary summer rainfall trends seem to have increased since them. The same is broadly true for the England-only data.
I knew very little about glow-worms before the Guardian’s article today piqued my interest. I am now slightly better informed, though still with a lot to learn. I note that others who know more than me, don’t blame climate change for the glow-worm decline. For instance, the Woodland Trustvi says this:
Whilst glow-worms remain fairly common, there is some concern about possible declines, and they have vanished from some sites. Possible threats include changes in land-use and habitat, use of pesticides, light pollution, and possibly parasites.
There are usually two sides (at least) to every story. Climate change may be playing a part in the decline of glow-worm numbers in the UK and firefly numbers globally. However, that part seems to be a lot less than the Guardian would have us believe.