Parasitic beetles: a threat to our glow worms?  

By John Horne                      

1. History of my glow worm research

This work was part of a long-term study (2001 to 2016) of glow worms (Lampyris noctiluca) at my nature reserve (The Secret Garden Nature Reserve) located at Old Bursledon, Hampshire (grid ref SU486091).


On 3 April 2006 I started to use an array of boards to act as shelters for the glow worms. I was pleasantly surprised by how quickly, and in what numbers, glow worms adopted the boards that we laid out for them. Out of 140 put down, 80 were used to pupate under and 46 had two or more pupating under, while two boards had nine under. (Figures 1, 2 and 3).



Figure 1

Glow-worm larva inspecting a board. It stayed in this position for five minutes before going underneath to prepare for pupation.



Figure 2

A cluster of five, all males, all at different stages of pupation. Date 29 May 2007



Figure 3

Female laying her eggs under a board on 29 June 2006. (Approx 75% eggs are laid in the first four days and it takes approx ten days to lay them all: Horne 2006–2016, unpublished)                                                                                                             


From our point of view the boards made it much easier to find glow worms at every stage in their life cycle: from eggs through to larvae and pupating to adults, male and female. We also found what we now know to be a parasitic beetle (approximately the size of a garden ant), and last but not least the lesser glow worm (Phosphaenus hemipterus). I first discovered this at 9 pm on 14 June 2007 under Board 59a which it was sharing with nine common glow-worm larvae pupating. At the time this was the only known breeding colony of P. hemipterus in the UK.                         

2. Observations of parasitic beetles attacking glow worms                                                                                                                                                                                                                                                                                                                                   

In the course of the 2006 season, two female pupae whose progress I had been following were found dead, with what appeared to be grubs of a fly or possibly wasp.



Figure 4

Pupating glow worm on 28 June 2006 – my first photo of the parasitic grub.                                                                                  

                                                                                                                                                                                             In the first case there were four grubs and in the second case, ten. We believe that they were parasitoids that had killed the pupae rather than as scavengers feeding on an already dead carcass, because both pupae had appeared perfectly healthy a short time earlier. Lloyd (1973) reported two species of parasitic flies (from the families Tachinidae and Phoridae) in other firefly species, but we do not know of any records from our glow worms.


The following year, on 29 May 2007, I found similar grubs on a female glow worm. I had recorded the same glow worm as a larva under the same board four days earlier, but at that stage had not noticed any sign of the grubs. Over the course of the next two weeks I found more than 30 glow worm pupae, males and females, carrying grubs of what appeared to be the same species, the last being recorded on 10 June that year. Some glow-worm pupae supported over 25 of these grubs, while others just inches away under the same boards appeared to have escaped totally unscathed. Within a single glow-worm pupa the grubs varied in size, with some three times the length of other grubs on pupating glow worms collected 5 June 2007.

Then on 1 July 2007 I found a small adult beetle crawling over a live adult female glow worm. When it reached the head the glow worm reacted immediately by flipping over as if trying to escape (Figure 5).  Subsequently, on 3 August 2007, this beetle was identified from the photo by Peter Hammond and Matt Shardlow of Buglife as Alaobia scapularis (Sahiberg) (Staphyinidae) beetle. Alaobia scapularis has been recorded from eight counties and three unconfirmed counties. Almost nothing is known of its biology. It is most often recorded from chalky areas, mirroring the same sites where glow worms are found.  Could this have something to do with the grubs that I had seen?                                                                                                                                     

igure 5

My first beetle, seen on 1 July 2007. At that time I did not know what it was. I started to get suspicious on 3 August 2007, but it was not till the next year, on 1 June 2008, that I found out that it was a parasitic beetle.


One of many notes in my diary, on 2 June 2007, refers to a larva under board 59/2 at 18:30. Its weight was 242 mg and it was still alive, and anything over 120 mg is guaranteed to be a female glow worm. It would have probably laid around 140 eggs (Horne 2006–2016, unpublished). But on 8 June 2007 its larval skin was off the end of its body, and it was now infested with grubs.


Notes from 2008


On 28 May 2008 I started seeing small adult beetles again. Then on 1 June 2008 in my diary I wrote: Very interesting. I saw four of the grubs around a pupating glow-worm larva which was still alive when I noticed that one of the grubs appeared to be biting at the glow-worm larva! This did not make sense to me, and unfortunately I did not follow this one through, as too many things were going on. On 4 June 2008 I found four adult A. scapularis beetles hanging around a large female glow-worm larva. I managed to catch them with the glow-worm larva and put them into a small tub. Later, at home, I managed to take some photos of a pair of beetles mating on the side of a glow worm (Figure 6 and Figure 7 close up). The glow worm was still alive, but very sluggish and at a point of no return into pupation. I managed to take a series of photos over the next 12 days. I will let the photos do the talking.


Figure 6

Taken 4 June 2008. Mating pair of beetles on the side of a very sluggish glow worm at the point of no return at 17:40. I was to see this in the wild many times over the next few years.


Figure 7

4 June 2008. Close up of the beetles


On 5 June 2008 I took them to the British Natural History Museum to meet Max Beckley who also confirmed this as a parasitic beetle and said I should do a report on my findings. Eight years later I am now doing it!


I did offer to leave the glow worm with the parasitic beetle in my tub with the Natural History Museum but they declined, saying that they are very good at preserving things that are dead, but are not very good at keeping things alive, so why don't you do it. I am so pleased I did this, but it was one of many things going on at that time.                                                                                                                                                                                                                                           

Figure 8

6 June 2008. The parasitic beetles are looking for signs of movement from the glow worm, or for their grubs. Time 20:02.


Figure 9

6 June 2008. This carried on for about 2 hours.


Figure 10

6 June 2008.  Testing for any movement?



Figure 11

6 June 2008. The beetle checking for any movement.



Figure 12

6 June 2008



Figure 13

6 June 2008. At 20:59 they appear to be getting quite excited and are now looking underneath the unfortunate glow worm. Then 43 minutes later in the next picture this happened.


Figure 14

6 June 2008. I was looking at some of these close-ups, and noticed what looked like the first grub, then the next photo shows it in a different position. This is at 21:43, and mating took place on the 4 June 2008 at 17:40, so you can say it only took two days from mating to a grub. The only thing is there were two pairs of parasitic beetle in there so I cannot guarantee that it took two days.



Figure 15

6 June 2008. You can see the different position.


Figure 16

Three days later on 9 June at 21:35 there is a visible grub, One thing that I cannot get over is how dedicated the parents are.


Figure 17 

9 June. Close up of the above. If the parents are the size of  garden ants then the grubs are like a fine hair.




Figure 18

Two days later from the last picture, on 11 June at 22:48, look how big they are now – quite amazing, I think. Note one beetle keeping an eye on things.


Figure 19

A day later on 12 June at 15.29.


Figure 20

Same day, at 15:35. Some holes in her back and one adult beetle in view. Notice that the holes are in the centre of the shields on each side.


Figure 21

Two days later, on 14 June at 19:32. Nearing the end now.


Figure 22

14 June, 19:35. The grubs are on the move getting ready to pupate.


Figure 23

On 15 June at 10:05 the last grubs are inside and outside, with nothing left but the shell.




Figure 24

15 June 2008. This is the last photo of this series of pictures.


Notes from 2009

On 8 June 2009 I took some photos of a female that was glowing and had attracted three males. In the photo just two males are showing. When I got home I looked at the photos and to my surprise there was a parasitic beetle on her shield. You can see how small this beetle is. It would be very interesting to see if any one else has taken a photo or has seen this. I just wondered what it was doing. In the series of photos to accompany this, there is what appears to be a start of a hole in the centre of one of her back shields on the photos.




Figure 25

8 June 2009. Close up.



Figure 26

8 June at 22:45, showing the parasitic beetle on her head with two males trying to mate with her.



Figure 27

Next morning, 9 June,  I found the female glow worm near to the spot I saw it displaying last night. This one was not under one of my boards. Note the start of a hole!





Figure 28

Close up of figure 27.


Figure 29

Now the beetle is at her rear end .




Figure 30

Close up of figure 29. Note that the female glow worm is mating with a male and the parasitic beetle is looking on – or is there more to this?


Figure 31

The parasitic beetle now on the male’s head – is he next?



3. A new discovery?

You could ask yourself, why has someone not discovered this before? To my knowledge no one has put boards down, and to try to find this out in the wild would be like looking for a needle in a haystack. How do the glow worms find the boards? In May the glow worms that are ready to pupate go on a walkabout. This iswhen people can see them wandering around in the day time. They are looking for somewhere suitable to pupate, such as a small hole in a bank, a crack in the ground or the fibre roots of grass, as well as many more places. When they come across a board that is about 6 ins by 10 ins or 15 cm by 25 cm the male or female will walk across the board more often. The boards act as a funnel to guide them in. The downside to this is that the parasitic beetle probably can do the same much more easily under these boards.


A threat to our glow worm?  

I personally think that this is a natural cycle and one reason why on average, a female  glow worm lays just approx 110 eggs each (Horne 2007/2016, unpublished). It is not a threat to our glow worms and is just part of life. Glow worms fluctuate year on year through peaks and troughs and the parasitic beetle keeps them in check.   When there are more parasitic beetles, glow worms numbers may drop, and when there are fewer parasitic beetles, glow worm numbers may rise.


Over the years, all my reports of this are from my diary and photos. It starts on about 15 May and finishes by approx 14 June with one exception on 1 July 2007 when I found a parasitic beetle investigating an adult female glow worm leaving the remainder to carry on and breeding in peace.



In conclusion, the above report is just a small part of the information I have about the parasitic beetle. I have included just the main points, and I also think the pictures tell you more of the story for themselves. I believe most of the report is new to science in the UK and possibly in the world.

What I have not found out is anything about the life cycle of grubs. I am open to suggestions on this. One thing I find very interesting is the parent beetles stay with the grubs until the grubs pupate. In the pictures they seem to be protecting them for at least ten days.


Finally, I wish to stress that I am very much an amateur naturalist with no formal training and my experience and knowledge have been built up through a lifetime of patient observation and an inquisitive mind.


John Horne, December 2016. Email:  

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