Field of Science

Barklice and Booklice and Such

Psocoptera is arguably the least deservedly obscure of the obscure insect orders. They're not uncommon - there's a reasonable chance that you'll have seen one in your life. You probably squashed it without giving much thought to what it was. And yet, so obscure is this order of insects that there isn't even a good vernacular name for the group. Psocoptera are minute insects (usually only a couple of millimetres long) that generally live among bark and litter, feeding on fungi. Some wingless species can be found in houses (where you might have seen one) and feed on such delicacies as dust or the glue used in book bindings, leading to their being known as booklice. The tree-living forms are sometimes referred to as barklice in comparison to booklice. Most entomologists that I know simply refer to the group as psocids, and that's exactly what I'm going to do.

Technically speaking, 'Psocoptera' is a paraphyletic group. The Phthiraptera, the true lice*, are derived from within the psocids. At the moment, things seem to be going through a transitional phase, with many authors dropping the paraphyletic 'Psocoptera' for the name Psocodea, which refers to the total group of psocids and lice. The 'Psocoptera' are divided into three suborders, the Trogiomorpha, Psocomorpha and Troctomorpha, the Phthiraptera being properly speaking a subgroup of the last. A representative of the second group, the psocomorph Blaste (photo from TOLWeb), can be seen at the top of this post, and it's the Psocomorpha that I'm looking at today.

*And holders of what is probably the worst insect order name of all to pronounce.

With over 3500 species, the Psocomorpha are generally regarded as the largest of the psocid suborders, though the Troctomorpha could give them a run for their money once the Phthiraptera are taken into account. We should probably be careful about making definite statements about this - because of their neglected nature, new species and sometimes even families of psocids continue to appear in the literature at a respectable rate. At the moment, though, it is a psocomorph that holds the honour of being probably the only invertebrate to get its picture plastered over Tetrapod Zoology, due to the nomenclatural issues that have arisen from the similarity in names of the psocid Caecilius and the amphibian Caecilia. The photo above is the one featured in Tet Zoo, and shows an identified member of the Caeciliusidae.

Most Psocomorpha are dwellers on bark or rocks. One group, the Caeciliusoidea, inhabits living foliage. Adults may be winged or wingless - many species have both forms. Many psocids cluster as nymphs - the photo above (from here*) shows one such congregation - and spin protective webs, but this is taken to the extreme in the genus Archipsocus. Archipsocus species form large colonies, and may build webs large enough to obscure tree-trunks, as can be seen in the picture below (from here). As with Embioptera, these colonies appear to be conglomerations of convenience, and there is no real social behaviour. Like aphids, Archipsocus may go through multiple generations in a summer, and the colony will contain individuals at all stages of development, both winged and wingless forms (Mockford, 1957). Once winter arrives, the colony breaks down and disperses, the survivors diapausing until the spring when they will start new colonies.

*This page also records a fantastic common name for psocids - "bark cattle", apparently because the nymphs move like a herd when disturbed.

Molecular and morphological data are mostly in agreement that the Psocomorpha can mostly be divided between four infraorders, the Psocetae, Homilopsocidea, Epipsocetae and Caeciliusetae (Johnson & Mockford, 2003; Yoshizawa, 2002). Both studies also agreed in placing Archipsocus outside these groups, as the basalmost member of the Psocomorpha. Unfortunately, beyond the bare morphology, information about most psocid groups seems to be few and far between, and there is a great deal about the order that we have yet to know.


Johnson, K. P., & E. L. Mockford. 2003. Molecular systematics of Psocomorpha (Psocoptera). Systematic Entomology 28: 409-416.

Mockford, E. L. 1957. Life history studies on some Florida insects of the genus Archipsocus (Psocoptera). Bulletin of the Florida State Museum - Biological Sciences 1 (5): 254-274.

Yoshizawa, K. 2002. Phylogeny and higher classification of suborder Psocomorpha (Insecta: Psocodea: ‘Psocoptera’). Zoological Journal of the Linnean Society 136: 371-400.


  1. I am developing a new fondness for psocids - we have a large and healthy colony in the bathroom, eating the mould that grows on the grouting in the shower. Yes really :)

  2. Working (as I do) for the milling industry, psocids are old friends!

    I stop them getting in my extensive collection of novelty flours by putting the flour in the fridge (or sometimes even the freezer), but I must see if I can train some to eat mould - that would solve a few problems in our house after the extensive roof flooding we had last year!

    We have a leaflet about them, if anyone's interested... ;-)

  3. Love your blog! The "barklice" are certainly better looking than the booklice. I'd love to correspond with any amateur psocid enthusiasts out there. I have been collecting in central Texas and east central Alabama for the last year. These insects are difficult to identify but they are interesting. Another article you might want to read "Multple Origins of Parasitism in Lice" Kevin P. Johnson, Kazunori Yoshizawa and Vincent S. Smith Proc. Royal Soc. London B 271:1771-1776, 2004.


Markup Key:
- <b>bold</b> = bold
- <i>italic</i> = italic
- <a href="">FoS</a> = FoS