The Heather Beetle Threat and How To Manage It
- Rob Beeson
- 4 days ago
- 5 min read
Heather beetle (Lochmaea suturalis) is posing a significant threat to the UK’s moorlands.
This seemingly unremarkable, small, olive-brown beetle, around 6mm long, has been grazing on heather for thousands of years. However, in recent times, outbreaks have become more frequent and intense, causing widespread damage and raising concerns about the health of our heather moorlands.
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A Year in the Life of a Heather Beetle
The heather beetle belongs to a large family of leaf beetles. When their populations explode, these beetles and their larvae can inflict devastating damage on heather plants.
Winter Dormancy: Immature adult beetles hunker down for the winter, hibernating in Sphagnum moss, heather litter, or even a few centimeters deep in the soil.
Spring Awakening: As the days warm up and the average temperature reaches around 9°C, the beetles emerge from their winter slumber, ready to feed on fresh heather shoots.
Dispersal: Being weak fliers, the beetles often rely on the wind to carry them to new feeding grounds. This can lead to damage appearing in narrow swathes across the moor, following the prevailing winds.
Mating and Egg Laying: Towards the end of April, females mature and begin laying up to 700 eggs in small clusters. They prefer to deposit these eggs on Sphagnum moss or other damp vegetation over a period of up to ten weeks. High humidity is crucial for the eggs to hatch successfully, which is why outbreaks often start near boggy areas.
Larval Stage: The Hungry Browsers: Within 1 to 4 weeks, the eggs hatch, and the peak emergence of larvae usually occurs in early July. These yellow-green larvae climb onto the heather and start feeding on the young shoots and leaves. This is when the most visible damage begins.
Pupation: After about six weeks of voracious feeding (around mid-August), the fully grown larvae drop off the heather and burrow into the soil and litter to pupate.
New Adults Emerge: Immature adult beetles may start appearing towards the end of August, but they become more abundant in late September.
Preparing for Winter: As temperatures drop below 9°C, the new adults become less active and eventually seek shelter to hibernate, completing the annual cycle. Notably, normal frost doesn't significantly harm any stage of the beetle's life cycle.
The Threat to Moorlands
Heather is the keystone species of many moorland habitats. These landscapes provide essential resources and shelter for a diverse range of wildlife, including birds like the red grouse, insects like the Emperor moth, and various mammals. Healthy heather also plays a role in carbon storage and water management.
When heather beetle populations surge, the collective feeding of countless larvae and adult beetles can strip vast areas of heather of their foliage. This can lead to:
Loss of Heather Cover: Severe infestations can kill off large patches of heather, leaving behind bare ground or allowing other, less desirable vegetation like coarse grasses to take hold.
Impact on Wildlife: Animals that depend on heather for food and shelter suffer when it declines. For example, the red grouse and the caterpillar stage of the Emperor moth rely on heather.
Economic Consequences: Damage to heather can negatively impact grouse populations and, consequently, the economic viability of estates.
Altered Ecosystems: Changes in vegetation composition can have cascading effects throughout the entire moorland ecosystem, potentially affecting nutrient cycling and other ecological processes.
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Factors Contributing to Heather Beetle Outbreaks
While heather beetles are a natural part of the moorland ecosystem in the UK, there's concern that outbreaks are becoming more frequent and severe. Several factors might be at play:
Climate Change: Warmer and damper springs and early summers can create ideal conditions for a significant build-up in beetle numbers. Conversely, cool, dry springs can inhibit egg-laying and slow down the spread. The hot weather and drought of recent years, coupled with milder winters that don't kill off as many larvae, have been linked to increased heather beetle damage. Extreme weather events, potentially linked to climate change, may also contribute to more severe attacks.
Moorland Management Practices: Large-scale outbreaks have occurred since the advent of modern moorland management, although long-term economic damage is often confined to wetter moorland.
Natural Enemy Fluctuations: The population dynamics of the heather beetle are also influenced by its natural enemies, such as the parasitic wasp, which lays its eggs in beetle larvae and can be a significant controlling factor. Ladybirds, spiders, and ants also prey on heather beetles at various life stages. Changes in the populations of these natural predators could affect beetle outbreak frequency and intensity.
Recognizing Heather Beetle Damage
It's not always easy to spot the heather beetles themselves, as they are small and well-camouflaged. In fact, extensive damage can occur without ever seeing a beetle. However, the damage they leave behind is often quite distinctive:
Stripped Stalks: Heather plants damaged by beetles often have their leaves completely eaten, leaving behind bare red or grey stalks with only a few surviving green shoots.
Widespread Damage: Unlike frost damage, which might be more severe in exposed areas, heather beetle outbreaks tend to be equally severe across sheltered and shaded areas. Historically, damaged heather was often mistakenly attributed to "frosting".
Fox-Red Colour: In the early autumn, heather damaged by beetles often turns a very distinctive fox-red colour. This orangey-brown discoloration can be a clear indicator of a problem.
What Can Be Done to Control Heather Beetle?
Managing heather beetle outbreaks is a complex issue with no easy answers. Traditional methods and current research offer various approaches, each with its own set of considerations.
Burning
For a long time, burning affected heather as soon as possible within the legal burning season was a common response. The rationale was that it would promote the regeneration of young heather. However, research suggests that burning may not be necessary for heather recovery after a beetle attack.
While burnt heather might recover quicker in the short term, after five years, areas that were burnt, cut, or left untreated showed similar levels of heather cover. Importantly, burning young heather might even make it more susceptible to future beetle attacks. Summer fires specifically to control beetles are likely to cause more harm than good.
Furthermore, damaged heather can be difficult to burn effectively as the lack of leaves hinders the fire from building up heat. In areas with deep peat, regulations may restrict burning, especially outside the controlled burning season.
Cutting
Cutting can be an effective way to manage heather after a beetle outbreak, either alone or combined with burning. It can help remove the dead heather canopy and allow regeneration from the remaining stems or rootstock, particularly if the heather was young and healthy. Studies have found that cutting did not necessarily lead to better long-term heather recovery compared to doing nothing.
Drainage and Other Moorland Management
Some suggest that drainage of wetter areas might reduce the likelihood of outbreaks, as high humidity is important for egg hatching. General moorland management practices like mowing, rotovating, and sod cutting could also be considered to reduce the risk of outbreaks.
Sheep grazing can also limit beetle numbers by creating a more open heather structure. However, more research is needed to determine the effectiveness of these approaches.
Looking to the Future
The future of UK heather moorlands in the face of increasing heather beetle outbreaks and the impacts of climate change remains a concern. Continued research, careful monitoring, and a focus on building resilient moorland ecosystems are crucial. Land managers need access to the best available information to make informed decisions about managing these valuable landscapes.
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