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Stag beetle, Rose Chafer & Cock Chafer 

Lucanus Cervus is the largest European beetle, the Stag Beetle, or as they are called in French “Le Lucane Cerf Volant”.  From around the beginning of June on warm evenings in France, often when humidity is high, we start to hear the drone of the males  as they make their clumsy and apparently impossible flights to seek out the females. The females don’t fly as often as the males, (if at all), tending to spend more of their time on the ground waiting for the males to find them. Sometimes more than one male will arrive attracted by the females pheromones, the males then proceed to “fight for the right” using their large antlers to wrestle with which happily rarely causes any harm as the weakest backs down and retreats from battle.

 Photo above of two male Stag beetles facing each other.

Most people I speak to seem to be at least a little bit fascinated by these spectacular creatures, particularly the males which have the large antler like mandibles and although these look rather threatening it is the female which is about half the size of the male and lacks the antlers who is more likely to give you a bit of a pinch if you pick her up; she is equipped with very powerful and sharp mandibles like clippers.  Should you need to move one out of harms way, from a road, a path or even from your house, it is best to nudge them from behind into a tin, plastic container or simply on to your hand and tip them out under a bush or by a tree, making sure that they don’t end up on their back.

Photo above of a Female Stag Beetle

After copulation has taken place the female lays her eggs on what is to be the food medium for the larvae. This is old, rotten wood lying on the ground or at the base of dead or partly dead trees, and although there is a preference for oak or chestnut other timbers will be used. The Stag beetle larvae, which can grow to a staggering 8cm and can also “nip”, live in the rotting wood for many years. The actual length of the life cycle is quite variable, possibly dependent on temperatures and can be 4, 5, 6, 7 or even 8 years resulting in a kind of insurance policy against bad years as well as providing genetic variety. They are classed as saproxylophages, creatures which live in dead and rotting wood.

Photo above of a pair of Stag Beetles mating.

In most of the regions of France the Stag Beetle is doing reasonably well although overall in Europe it has declined and is now scarce in many parts of its previous range.   Jean Henri Fabre, 1823–1915, French entomologist and author, reported that he easily filled a top hat with them in one evening, which is unimaginable now even if you took a month where they are plentiful.  Land clearance for agriculture is clearly one reason for the decline as is the increase in coniferous commercial woodland, other likely reasons are that we are probably just to tidy in urban and peri-urban environments, very little wood is left lying around to rot in parks and gardens, wood used for fence posts and the like is usually chemically treated, old trees are removed including the stumps and roots before completing their full life cycle and hedgerows which contain a large quantity of dead wood and debris at their base have also been removed.  As stated above, we are fortunate in many parts of France which may be due in part to the rotational coppicing for firewood on a 20 to 30 year cycle which leaves quantities of dead wood and stumps in situ. Never the less every effort should be made to maintain this species in its continuing strongholds.

Partly developed Stag Beetle larva

Another creature that buzzes loudly around our French gardens on long, hot summer days is the stunning Rose chafer and surely everyone has seen them; metallic green, bronze, blue or purple splashed with a few little white spots or dashes. Nature has a way of creating the most amazing colours.  The adult beetles that are about 20 mm long are to be seen clinging to flowers where they eat pollen and nectar and generally rummage around, something rose lovers can get a bit heated about although in reality many other flowers are visited, with native species such as thistle and bramble being favoured. However it’s the larvae that cause most concern and they are a continual source of confusion and misunderstanding for people that mistake them for the larvae of the Common Chafer or May bug as many will know them, (or indeed for Stag beetle larvae). To get to grips with this we need to understand their different biology and life cycles.

Photo above of a Rose Chafer Beetle.

Following mating the female Rose Chafers lay their eggs in decaying organic matter and then die. This is why people find the grubs in their compost heaps and sometimes in plants, shrubs and trees that are purchased in pots. The larvae spend their lives and develop where the eggs have been deposited which will be in compost, manure, leaf mould, and occasionally well rotted wood where they are the equivalent of earth worms and help break things down so in this respect  they are very beneficial. They don’t eat living roots, only decomposed or decomposing vegetative matter. They grow very quickly and will have moulted twice before the end of autumn. They have a two-year life cycle and they pupate in June or July of the second year when it’s possible that some adult beetles may emerge in autumn, but the main emergence is the following spring and early summer, when the beetles mate.

Photo above of a Rose Chafer larva found in compost.

Cock Chafer adults emerge in April / May and live for perhaps 6 weeks although frequently less. During this time they mate and females then bury their eggs about 10 to 20 cm deep in the soil in different places with up to 80 or so in total. What’s important to understand here is that the Cock chafer eggs are usually laid in undisturbed old unmanaged grassland in poor soil. This can lead to problems where they are present when old grassland is initially converted into vegetable beds where they may eat roots. The larvae are polyphagous; they attack the roots of various plants including potatoes, meadow grasses and trees.  In fact historically they were a major agricultural pest and following the use of vast quantities of pesticides including DDT and Lindane their numbers have been drastically reduced and they are completely absent in many areas. Mercifully these pesticides have been banned now in the EU as have all applications of pesticides that function in the soil and numbers are slowly increasing. The larvae once hatched develop in the soil where they eat roots for 3 to 5 years at which point pupation takes place in the autumn and the adults emerge the following year.

Photo above Cockchafer or "May bug".

So how do you as a gardener know which big fat juicy creamy white grub, (larvae), is which? Visually there isn’t a great difference between the three of them unless you are going to look closely which I suspect most people won’t BUT we can make it simple and more or less foolproof and if you bookmark this you can refer to it in the future.

Stag beetle grubs or larvae are 99% certain to be found in rotted or rotting wood; normally this is quite large branches or trunks that are on or partly in the ground where they remain constantly wet or damp.

Rose chafer grubs are 99% certain to be found in compost, leaf-mould, manure heaps and fibre rich soils. Occasionally they can be found in the same habitat as Stag beetle larvae where the wood is extremely degraded. They are frequently blamed for the death of plants in pots because people think they eat the roots – they don’t. What can happen is that they eat the compost and there isn’t enough nutrition left for the plant but this only happens when the plant is in too small a container.

Cock chafer grubs are always to be found in ordinary soil, usually lawns and grassland, but remember they are quite scarce or rare in many places and they are never to be found in decaying wood or the compost heap.

As a final point, none of these large larvae can be confused for being vine weevil larvae that can sometimes be found in the roots of plants. Vine weevils grubs are really quite small being no more than 10mm at the most.

Some general conservation advice:

If you have veteran trees, try to leave them standing, or if you do need to cut down trees, try to leave the stumps in place to decay. Try to maintain a native species hedge if you have one, or if you have land consider planting a native species hedge. Make a log pile in a corner of your garden, perhaps by sparing a few lengths of oak from your firewood delivery if you have one and add to it each year allowing it to slowly rot; the addition of bark, wood chippings and sawdust will be useful, it is important that the bottom remains in contact with or slightly buried in the soil. This can be discreetly hidden behind a bush or shrub or made into a decorative garden feature for those with an artistic leaning.  You could perhaps also empty all your grass cuttings in a heap alongside your “wood pile”.

All of these measures will benefit many other species and encourage biodiversity and add to the buzz in your garden.  It should be made absolutely clear that none of these larvae pose any threat whatsoever to dry seasoned wood in your buildings; only moist decomposing wood will be used outside on the ground.

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