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Byrrhidae – Pill Beetles

A small family of beetles that I am very fond of. So-called because of their ability to retract their head and all of their appendages into matching grooves on the body. As smoothly ovoid ‘pills’, they achieve some camouflage, resembling seeds or rabbit droppings. This behaviour also makes them laborious to card properly, as each appendage must be hooked out individually.

Cytilus sericeus in 'pill' posture

They don’t seem to have been very popular with coleopterists through the decades, perhaps due to the particular difficulties of carding them. When Colin Johnson took an interest in the family he was able to add two species to the British list:

  • Byrrhus arietinus (Johnson, 1966b)
  • Curimopsis nigrita (Johnson, 1978),

and to bring a third out of obscurity:

  • Simplocaria maculosa (Johnson, 1966a; 1978)

The British list now stands at 13 species in 7 genera in the Duff (2008) checklist.

To identify the British species of Byrrhidae and the single similar species in the family Limnichidae, please download these updated keys (version 5, 29th March 2013). Version 5 now has a complete set of photos of the aedeagi of the four Byrrhus species, thanks to Martin Collier.

To download the keys, left-click the link. This will take you to my Google Docs webpages where you can see an online preview of the document (in which some of formatting and pagination isn’t right). From the File menu, select Download and Save the file to your computer to see it in its original form.

As I understand it, byrrhids feed on mosses, as larvae and adults, and are the only British beetles to do so. There seem to be amazingly few moss-feeding insects, despite the huge variety of species that feed on flowering plants. From my observations, I’m sure that Byrrhus pilula and probably all the larger pill-beetles feed on pleurocarpous mosses, whereas I suspect that the smaller species (Chaetophora spinosa and the three Curimopsis species) may prefer to feed on acrocarpous mosses. But saying that, I have a record of Chaetophora spinosa “on rock next to pleurocarpous moss (Whitish Feather-moss Brachythecium albicans)”. Brian Eversham tells me that Curimopsis nigrita has a strong preference for Forklet-mosses Dicranella species (acrocarpous mosses).

I’m not aware of any detailed work being done on the feeding preferences of byrrhids, probably because no coleopterist has ever been able to identify mosses properly, and vice versa for bryologists. But nowadays there are a few pan-species naturalists who are familiar with bryos and beetles. So if you have any information, now or in the future, on the food-plants of byrrhids please add it as a Comment beneath this page.


Johnson, C. (1966a). Taxonomic notes on British Coleoptera. No. 4 – Simplocaria maculosa Erichson (Byrrhidae). The Entomologist, 99, 155 – 156.

Johnson, C. (1966b). The British species of the genus Byrrhus L., including B. arietinus Steffahny (Col., Byrrhidae) new to the British list. Entomologist’s monthly magazine, 101 (for 1965), 111 – 115.

Johnson, C. (1978). Notes on Byrrhidae (Col.); with species reference to, and a species new to, the British fauna. Entomologist’s record and journal of variation, 90: 141 – 147.


  1. Jim Jobe says:


  2. markgtelfer says:

    Jim, Dave: much appreciated.

  3. Clive Washington says:

    I have frequently found Cytilus sericeus by vacuum sampling in moss but there are usually half a dozen moss species present so it’s hard to work out which, if any, is important. I’m still struggling with the new bryophyte handbook – some mosses are distinctive but many of them are awfully similar!

  4. Rik Harris says:

    Thank you

  5. markgtelfer says:

    Peter Kirby has been in touch with three more recent records of Porcinolus murinus: Holt Heath, Dorset, SU0504, 7 June 1981; Sandringham Warren, West Norfolk, TF6728, 1 July 1988; and Plumley Wood, South Hampshire, SU117099, 17 July – 7 August 2003 (pitfall trap).

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