Bog Myrtle & Peat

After posting about heather beetle a few days ago, a few readers have been in touch looking for more information on the subject. As a bit of a disclaimer, there is a great deal of information that we just don’t have about heather beetle. Some fairly fundamental facts are just missing when it comes to looking at the problem, so I can attempt to answer some basic questions here with the “get out clause” that if I’m wrong, then it’s because nobody knows what is right*. (*I could also just be plain wrong…) I have no hesitation in pointing people who want to know even more about heather beetle to the Heather Trust website, where new info relating to outbreaks and damage is updated frequently.

As far as the beetles themselves go, there is nothing really remarkable about those little insects. They eat heather leaves and go about their lives in a perfectly boring manner. What is remarkable is their ability to explode into huge numbers apparently without provocation. In a normal year, some heather plants are slightly damaged by beetles because it is the nature of moorland that everything should take its turn at being munched. During an outbreak of heather beetle, millions of beetles strip the leaves off heather plants over thousands of acres, killing them outright or leaving them to dwindle back to a gradual demise.

Adult beetles hibernate during the winter in plant litter, and become active in the spring, when the mean daily temperature rises above 9 degC. The beetles then leave the litter and climb up into the heather leaves, attempting to disperse into areas of fresh heather which was not damaged by last year’s outbreak. They flex their little wings, then take to the sky, being blown by the wind for some distance. During this time, it’s not impossible for up to 2,000 individual beetles to be found in every square metre of heather, and it can present a daunting spectacle for people who see the mass dispersal of millions of beetles. It is important to note that the beetles don’t seem to be in control of where they are going, and the damage they cause often appears as long narrow streaks which move gradually down wind. Because beetles are present in all areas of moorland, there is no chance of outbreaks being spread artificially by public access to heather as may be a factor with “blaeberry blight” (or phytophthora), and the only thing which can initiate an outbreak is the beetles themselves.

Following a short period of dispersal and mating, eggs are laid at some point between April and June, and they usually hatch in July. The adult beetles die off after they have laid their eggs, and there is only one generation of eggs every year. The beetle’s reproductive processes require access to reliably damp conditions, and it seems like there are more beetles on wetter ground which is dominated by sphagnum. Infact, outbreaks often seem to start on the margins of sphagnum moss, making it look like wet flushes are to blame. In the old days, some moors responded by draining wet flushes so that they were less useful to beetle populations, but nowadays it’s generally hard to balance the advantages of this work with the many disadvantages of drying out peatland and limiting the number of insects available for grouse chicks.

Once the eggs have hatched, the larvae climb up into the heather plants and dine out on the leaves, going through a few different phases and finally falling off into the leaf litter to  emerge as adult beetles towards the end of August. By this stage, much of the damage has been done to the heather, but the adult beetles still need to be fed. As the autumn approaches, they munch on, then finally tumble down into the leaf litter once the temperature drops below an average of 9 degC again. Outbreaks tend to work on short cycles of just a few years until natural mechanisms kick in and kill off the majority of the beetles. They are predated upon by a species of wasp which kills them off by the dozen, but these wasps need time to build up sufficient numbers to have any noticeable effect. On many moors, the worst of the damage happens in the first, second or third years, then dwindles away into nothing again as the beetle population collapses.

We don’t understand why beetles go through these huge blooms, but it seems like it is a natural response to a fairly unnatural habitat. After all, heather did not evolve to form tremendous monocultures which sweep over thousands of acres, and it’s only human intervention which has made the moorland we know and love today. As a result, the habitat we have created is peculiarly vulnerable to these outbreaks, and our response to them should be based more on learning how best to restore damaged heather than the careful destruction of a species which damages it. Fortunately, we are getting close to some fairly advanced techniques for restoring heather which has been damaged by beetle, and patching up the damage is not only the most practical way of dealing with an outbreak but is also the the most ecologically sound direction to pursue. For grouse moors with a vested interest in heather, the future of heather beetle damage holds a great deal of hope.

However – there is a rather prickly nettle to grasp when it comes to moorland that is not managed for grouse – if a heather-clad sheep farm is severely damaged by beetle (as it may well be given that the nature of the undergrowth on a farm could well be quite uniform and unmanaged, lending itself to a more serious or extensive attack), where is the incentive to repair the damage? If you lose the heather from a grouse moor, it cannot function. If you lose the heather from a sheep farm, you have white grass which the sheep will still eat. Grouse moor owners will move heaven and earth to keep the heather on their land, but they are fairly unique in that respect. Uncovering ways of restoring damaged heather is one thing, but making it cheap, easy and worth the bother for someone who is as happy with grass as he is with heather is another thing altogether. Without jumping too far ahead, our ultimate priority should be to create a number of different techniques for restoring beetle damaged heather which finally become so well-established and scientifically robust that farmers, foresters and non-shooting landowners will be able to apply for funding to pay for them.