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How stag beetle Lucanus cervus larvae feed

by Paul Hendriks and Maria Fremlin.

Stag beetles spend their larval stage feeding on decaying wood, they are a saproxylic species.
In this page we describe the way in which the larvae of a particular species - Lucanus cervus - feed in captivity when they are much easier to observe.  
All observations were made by Paul Hendriks who reared them.

Drawing by Paul Hendriks Starting from the top larva and following the direction of the arrows, the drawing on the left shows the way that a larva of this species feeds inside decaying wood. The stag beetle larvae will usually start by scraping the surface of this wood. They do this by moving their sharp jaws (mandibles) down (top larva, bold arrow) and so scraping out small splinters of wood.

The next step (middle larva) is that the larva will search this scattered wood for edible splinters. This is done by just picking splinters from the scratched surface. Or by searching the splinters around itself and eating the suitable ones. A larva in a “bad” substrate can constantly be busy with scraping and searching, but will feed little. Larvae in a “good” substrate, for example, white-rot, usually will scrape little and feed much. They therefore have little loss of energy and grow well.

After some time (varying from some minutes to sometimes an hour or so) the larva shuffles away the splinters with its head to the other side of its hole (bottom larva). This way larvae clean up the part they have searched for edible splinters. Then, they turn around and start again, (top larva).

This is only a general description of the way the larvae feed. Of course, their position often varies as well as the time they spend.

Now, let us look at illustrations of these feeding strategies in white-rot decayed wood. If the wood has been infected with this type of rot it will turn softer after a while, in which case the larvae will easily scrape its surface.
If you pass the mouse over the larvae photos will get information about their age (time since hatching), instar/HCW, weight and the photo date.
5 months, L3/hcw=~10 mm, ~10 g. Photo 6 January 2007, Paul Hendriks On the left, you can see a stag beetle larva in action. It has been scraping the wood.  

The larva follows a “flame” of white-rot, surrounded by the darker mould. The white-rot can be seen just to its left in the picture (red arrow).  

The larva is now busy pulling the splinters backwards. You can see these splinters lying underneath it.
5 months, L3/hcw=~10 mm, ~10 g. Photo 6 January 2007, Paul Hendriks
In the picture on the left the larva is searching the splinters for suitable ones to feed on.  
It is hard to tell how the larvae pick the splinters they feed on. Visually, these splinters look very similar. When you look close at a searching larva, however, you can see that it examines the splinters carefully with its mouth-parts.  
It is important to realize that these stag beetle larvae do not feed on all the splintered wood, but select their food from it.  
Afterwards a larva may return to the place where it had been splintering wood before. Then, it often starts feeding again on the same material.
5 months, L3/hcw=~10 mm, ~10 g. Photo 6 January 2007, Paul Hendriks
Here the larva bites into the wood. Once it has selected a splinter, it will swallow it intact. To start with these splinters have always about the same size. They measure around 3 to 4 mm in length and are 1 or 2 mm broad.

In Germany stag beetles are aptly called Schröter, an old word meaning the man who prepared the grain for the miller by threshing the ears, the thresher.

5 months, L3/hcw=~10 mm, ~10 g. Photo 6 January 2007, Paul Hendriks
Here is a special occasion when the larva produces a faecal pellet looking like a sort of compressed pallet or pillow.  
Notice that the larva is now lying in the opposite direction. The pellet is almost the colour of its head capsule.  
5 months, L3/hcw=~10 mm, ~10 g. Photo 6 January 2007, Paul Hendriks
A faecal pellet is often picked up with the mandibles and front legs and pushed to the other side, away from where the larva was feeding. It moves the unwanted splinters the same way.  
By continually doing so, it moves forward through the dead wood and creates tunnels, stuffed with splinters and pellets (see next picture).  
By volume, the ratio of splinters-to-pellets in these tunnels may vary from almost 0 to 6; on average it is about 3.  

Photo by Paul Hendriks
On the left is an example of a beech Fagus sylvatica log infected with white-rot in which a stag beetle larva had been feeding and in the process left one large irregular shaped tunnel stuffed with debris (which have a darker colour than the wood).  
As the larvae push the splinters with some force, these tunnels can get densely packed not only with splinters but pellets as well.
All larvae of the Lucanidae family do this, however, the cavities left by this species in the wild are so characteristic that one can determine with confidence their presence even when the larvae are no longer there.

All of the above has been about larvae feeding in a log, however stag beetle L. cervus larvae in the wild have sometimes been found in very fragmented wood mainly woodchips.  
Therefore let's look at their feeding strategies in this substrate (pabulum).
In woodchips there is no need to scrape hard, the larvae will mainly splinter the chips and feed on the wanted particles. If the larvae have little to feed on they will splinter the chips again and again until they become a fine mould.
Below is an older larva in the “feeding position”; it is surrounded by well decomposed dark woodchips.
This larva has not fed on anything else and by now it has accumulated a lot of yellowish fat tissue.
12 months,L3/hcw=10.9 mm, 18 g. Photo 16 August 2009. Photo Paul Hendriks Interestingly, in this particular woodchips there were practically no pellets to be found, moreover, once a larvae was seen re-ingesting a pellet. This is proof that the larvae were mostly re-ingesting them. Why?

Well, if you look at the lower part of the body of the larva on the left, you notice that it is rather distended; this is its rather bulky hind gut which works like a large fermentation vat.  
It is where the wood is slowly digested with the aid of micro-organisms.

So the answer is that, probably, in this case the pellets may still have contained valuable undigested material therefore were well worth re-ingesting.

This is an interesting feeding strategy that, as far as we know, has not yet been reported for this species.

Regarding the observation about the larvae re-ingesting of their own faeces, this is not uncommon in animals that feed on plant material as it allows for the further digestion of poorly nutritious food. Let's look at some stag beetle cousins that are known to do it.

For instance, some dung beetle larvae, which develop inside brood masses, feed and defaecate over and over in that confined space; analyses on the microbial content of their gut and the brood mass gave identical results [1]. Like stag beetles, they also have a distended lower gut, which functions as a large fermentation vat. For example, see a larva of a minotaur beetle, Typhaeus typhoeus, by its moist brood mass (made out of rabbit pellets).

Other examples are the subsocial bess or passalid beetles whose adults and larvae live together in rotting logs. The adults feed their larvae with regurgitated food and faeces [2]; the larvae have very weak mandibles and are totally dependant on the adults. Interestingly, they do not have a distended lower gut, see this example. Their external surroundings become a sort of “external rumen” [3]. As a result of being fed such pre-digested food the larvae develop very fast; thus their life cycle is much shorter than that of the stag beetles, just a few months. The Horned Passalus, Odontotaenius disjunctus, larvae take about 2 months to reach maturity [2].
Exceptionally, the only stag beetles which exhibit parental care, the Figulini, also have a larval stage with an identical duration of the bess beetles [4]. Whereas L. cervus larvae, who have to fend for themselves, may take at least 2 calender years to develop.

The stag beetles, together with the dung and passalid beetles, belong to the superfamily Scarabaeoidea, so they are all related. They are nature's decomposers and have evolved ways of recycling organic matter most efficiently but there is a lot of work still to be done in order to fully understand their ways.

If you found this page interesting then we would love to get some feedback from you. Just contact Maria Fremlin!

[1] Cambefort, Y (1991) - From saprophagy to coprophagy. In: Hanski, I. and Cambefort, Y., Editors Dung Beetle Ecology, Princeton University Press, Oxford, pp. 22-35.
[2] Schuster, JC & Schuster, LB (1997) - The evolution of social behavior in Passalidae (Coleoptera). In: Jae C. Choe, Bernard J. Crespi, Editors Social Behavior in Insects and Arachnids, Cambridge University Press. pp. 260-269. Google Books Link
[3] Suh SO, Marshall CJ, McHugh JV, Blackwell M (2003) Wood ingestion by Passalid beetles in the presence of xylose-fermenting gut yeasts. Mol Ecol, 12(11):3137-3145. [PDF]
[4] Mori, Hideaki, Chiba, Satoshi (2009) Sociality improves larval growth in the stag beetle Figulus binodulus (Coleoptera: Lucanidae). European Journal of Entomology, 106:379-383. [PDF].

Feeding stag beetle (Lucanus cervus) larva, by Paul Hendriks.
Stag beetle (Lucanus cervus) larva reacting to being disturbed when the bucket it was in was upturned, by Maria Fremlin.
Feeding rhino beetle (Oryctes nasicornis) larva, by Paul Hendriks.

Last modified: Thurs Mar 07 2017

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