Pheromones or ...?

I’ve noticed that when I get Common Cockchafers (Melolontha melolontha) in the moth trap there are very rarely other species in the trap. This can persist for a few days after the last Cockchafer has been evicted. It seems to have happened too often to be down to weather conditions and low moth numbers though I have to admit I’ve not recorded the weather conditions…

I’m beginning to wonder if other species are actively avoiding the Cockchafers. That begs a few other questions …
… how do the other species detect the Cockchafers in the trap? Pheromones?
… are adult Cockchafers predators of moths?
… do the Cockchafers attract other moth predators?

I’m going to try taking a note of the weather and replacing the egg-boxes in the trap. Any other suggestions?

That’s an interesting observation.
I think that pheromones must play an important role in the life of a Cockchafer - their antennae being so well-developed suggest this. Also, pheromone traps are frequently employed to control them. There are several known Cockchafer pheromones (1,4-benzoquinone (M. hippocastani) and toluquinone (M. melolontha), and it’s known that phenol, and mixtures of phenol with the leaf alcohol (Z)-3-hexen-1-ol also attract them. See That suggests that they may secrete enough chemical (or the right ones) to deter moths. But I don’t know how varied moth pheromone production/detection is.
Another point is that - as you mention - those well-known moth predators, the bat family, also seek out Cockchafers. So they may choose to hunt in an area where such as large meal has been found.
Cockchafers are a fairly uncommon UK species these days, in my limited experience. So it’s worth noting that in the past, they were a considerable pest. In 1574, cockchafers emerged in such numbers in the Severn valley that the volume of carcasses disabled several watermills. (“I think we’re going to need a bigger moth trap.”)

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For what it’s worth, I have some statistics from the last couple of years in respect of my own moth trap in Box, Wiltshire,
7.5.2017 28 cockchafers, 17 moths representing 12 species
19.5.2017 9 Cockchafers, 2 moths, 15 species
22.5.2017 11 Cockchafers, 50 moths, 27 species
31.5.2017 5 cockchafers, 46 moths, 26 species
3.6.2017 2 cockchafers, 25 moths, 16 species
Then no more chafers until this year
6.5.2018 1 Cockchafer, 17 moths, 9 species
14.5.2018 14 cockchafers, 22 moths, 9 species
20.5.2018 20 cockchafers, 42 moths, 20 species
27.5.2018 4 Cockchafers, 46 moths, 15 species.
Probably not a long enough run of observations to be statistically significant, but I can’t see any particular correlation between cockchafer numbers and moth numbers here. I hadn’t thought of replacing my egg boxes, but sounds like a good way of testing the hypothesis.
That’s an amazing bit of historical information about the Severn Valley - do you happen to know what the historical source is?

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Correction - Second line should be
19.5.2017 9 Cockchafers, 22 moths 15 species

It was found in a quick internet trawl for the pheromones issue, at Other tidbits from there were:

  • (You also probably knew this) another name for them was “doodlebug” - later applied to the V-1 in World War II.
  • The young Nikola Tesla used four cockchafers to power an electric motor.
    See also this one - - “…1320, when the cockchafers (as a species) were taken to court in Avignon where they were ordered to leave town and relocate to a specially designated area, or be outlawed. All cockchafers who failed to comply were collected and killed. Both adults and grubs have been considered a delicacy at times and are still eaten in some countries.”

Do any of those web links have the original details to those old (1320, 1574) references e.g. who was writing about cockchafers in those times.

The very nicest things about iSpot (unlike that one) is the community spirit, seen and felt through the main site’s Comments sections and now here.

Thanks Amadan; that’s fascinating. I looked at Marren and Mabey’s Bugs Britannica (a useful source of historical information and folklore) which also notes both the Avignon and Severn infestations, but frustratingly does not indicate the primary sources. But the Avignon trial is entirely plausible; I recall that there are other instances pre-Reformation of animals being the subject of judicial process!

Sorry, no: only what I’ve linked above.

Digressing from Pheromones
There is a ref. to the 1574 'roach '‘plague’ in this
Search for 1574 and find nearby “In 1688, in the county of Galway, in Ireland, they formed such a black cloud that the sky was darkened for the distance of a league, and the country people had great difficulty in making their hay in the places where they alighted.”
Entomologists ‘Kirby and Spence’ seem to have published widely in the early 1800s - see, typically,

My apologies for not responding sooner: I blame the confuser! Many thanks to all who have contributed.

Jonathan, I guess that blows my theory clean out of the water. I think what’s left is purely a shortage of moths :frowning: Perhaps we’ll see more when the current run of Easterly winds gives up and we lose the East coast haar.

Fascinating the research others have done on various tangents. I was relating some of the facts in a local court today, much to the merriment of my colleagues. Somehow I don’t imagine Cockchafers appearing on a court list here any time soon.

I presume that these poor beasties have been the subject of some pretty serious chemical and physical attacks over the years in view of their propensity to damage crops. Thankfully such attacks don’t seem to have pushed them to the edge of extinction though I note that until I started reporting them three or so years ago, they hadn’t been reported in Midlothian since the early 1900s.

That book on project gutenberg is certainly worth a read about cockchafers. Wonder if they will become such pests again as I think their numbers are on the rise.