What’s up with British moths? Like much of our wildlife, they’re being hit hard by habitat loss and responding to warmer weather. Richard Fox and Tom Oliver explain. Much ado about MOTHS

e hear a lot about the global of insect populations and distributions considerable technical challenges involved declines of animals from honey are rare. In Great Britain, though, we’re because the moth records are not gathered Wbees to elephants. These are fortunate enough to possess just such through systematic survey – they are simply important species, but does their plight tell information on the larger moths, thanks to sightings of moths whenever and wherever us anything about the wider state of the a long tradition of natural history study by encountered by the recorders, and so vary millions of other species that make up the dedicated amateur enthusiasts. Moths are greatly both geographically and from year Earth’s biodiversity or about the benefits a major branch of the insect tree, so there to year. that this biodiversity generates, including are many different species, and they also If we’re not careful, such biases can food, clean water, fertile soil, pollination and form important links in food chains and act lead to false conclusions that species have so on? as plant pollinators. colonised new areas over time, or that Scientists usually assess biodiversity We used 11 million recorded moth certain colonies have become extinct, when based on a few groups of animals, such as sightings, made by knowledgeable amateur the reality is just that recorders happened mammals and birds, that are relatively large observers for Butterfly Conservation’s to visit a particular area one year and not and popular and, consequently, well studied National Moth Recording Scheme, to the next. We used an innovative approach, by humans. Yet these groups are almost calculate long-term population trends for recently developed at CEH, to adjust for irrelevant compared to the enormous Britain’s larger moths. Although previous this kind of uneven recording in our analysis. diversity and sheer abundance of other studies based on different data have done The overall picture for British moths types of wildlife – particularly insects. this for widespread, nocturnal moths, this is is gloomy. Larger moths, as a group, had It may be that the trends of birds the first time it’s been done for all Britain’s declined significantly over the period. mirror patterns of change among beetles, resident larger moths – day-flying and Examining each species in turn showed butterflies and bugs – but, equally, they nocturnal, rare and common. that 260 had decreased significantly. Only may not. If we really want to know about The study, which was conducted by a 160 had increased significantly, with the the state of our wildlife, whether in our team from Butterfly Conservation, NERC’s rest showing no clear trends. So two-thirds gardens, our nations or our planet, we need Centre for Ecology & Hydrology (CEH) and more of our larger moth species declined to understand what is happening to insects. the University of York, determined changes than increased. But it’s no coincidence that past in the occurrence of 673 larger moth Beyond this gloomy, if not altogether assessments have been based on furred species in Britain over the four decades surprising, result, the analysis revealed and feathered animals; detailed datasets from 1970 to 2010. There were some interesting patterns of change that

Lime Hawkmoth. Moth trapping. Shane Farrell Dave Green

26 PLANET EARTH Spring 2015 Archer's dart.

Chris Manley provide clues as to what might be behind these trends. It is likely that many factors If we really want to know about come together to influence each moth’s population and distribution, but our results the state of our wildlife, we need to suggest substantial influences of both climate change and shifts in land use such as understand what is happening to insects. more intensive farming. ❝

North versus south distributions are probably not too sensitive the causes of the British moth trends that Many moths are limited to just northern or to the climate, only decreased in southern our study revealed, let alone addressing just southern parts of Britain. Among those Britain where more habitat has been lost them. But the overall picture of decline is that only live in more northerly, colder and degraded as farming has become more as clear in this diverse insect group as it is areas, almost all had decreased since 1970, intensive. This includes the removal of among the few high-profile creatures that which matches what you might expect to hedgerows and field margins and increased garner media, celebrity and political interest. happen as the climate gets warmer. use of pesticides and chemical fertilisers. In Restoring the habitats that have been Species associated with the warmer northern Britain, where much more wildlife damaged by human activity – for example, southern half of Britain, on the other habitat survives, there was no overall replanting hedgerows, allowing mature trees hand, might be expected to have benefited pattern of decline. to develop in hedges and encouraging the from climate warming. Yet these species There was even more support elsewhere ecologically-sensitive management of farm also have to contend with high levels of in our findings for the idea that land- field margins, road verges, urban parks and habitat degradation in the more intensively- use change has a major impact on moth other green space – would be a first step managed south, which probably harms trends. Moths, such as the cistus forester, to counteracting the declines of moths and moth populations. In agreement with these associated with open grassland habitats other pollinating insects. expectations, we found that southern and low levels of soil fertility (nitrogen)

moths showed a variety of trends, with a – usually because the plants they need as Library Picture Hyde/Nature caterpillar/Alex moth Magpie and Hawkmoth mixture of increasing and declining species caterpillars (common rock-rose in the cistus and no overall pattern. forester’s case) grow only in these habitats Widespread moths – those found – tended to decline. In comparison, moths throughout most of Britain – decreased on associated with taller vegetation and more average, but when we looked at the trends fertile conditions, such as the snout whose Richard Fox is surveys manager at of these species separately in the north and caterpillars feed on nettles, tended to Butterfly Conservation. south, we found most had declined only in increase. This finding suggests that nitrogen Email: [email protected] the south. In northern Britain, there was pollution of the environment, known as Dr Tom Oliver is an ecologist at CEH. no overall trend – some species declined eutrophication, may be influencing moth You can read the full study at and others increased. It is interesting, and trends. Eutrophication is a consequence of i http://onlinelibrary.wiley.com/ perhaps informative, that these widespread intensive farming and vehicle emissions. doi/10.1111/1365 -2664.12256/full moths, which by nature of their extensive We are still a long way off understanding

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