Most of the creatures described in this column are from insect orders like Diptera (flies) or Coleoptera (beetles) that have hundreds of thousands of species. This week’s subject is from a smaller order with around 11,000 species. It’s the bark louse.

Before you stop reading, please note: Bark lice are not head lice. They feed on the algae and lichen on trees and have no interest in hiding in your hair.

The bark louse order has been renamed a few times. They were first part of the true bug order (Hemiptera), then given an order of their own called Psocoptera, which in Greek means gnawed or rubbed wing. Now, they’re part of the Psocodea order, along with book lice and parasitic lice (also not head lice, they’ve been given their own order, Phthiraptera). 

One common species in Oregon, Graphopsocus cruciatus, is thought to have been introduced to the West and East Coasts in the 1930’s and has been slowly spreading inland. It’s easy to identify because of the F-shaped marking on the wing. 

Because bark lice spend the winter as adults, you can find them on sunny days during November and December. You’ve got to look close, because most are less than a quarter inch long. The other species shown here is, I believe, in the Teliapsocus genus. 

There are some undeniable oddities in the Psocodea order. Some bark lice (nymphs and adults) spin irregular webs on tree bark. In other species, the females have reduced wings or no wings at all. And, like aphids, some bark lice give birth to live offspring, while others are parthenogenetic and do not need males to reproduce. 

I can’t end without mentioning an east coast variety of bark louse (Cerastipsocus venosus), which often gathers in large numbers of nymphs and adults to feed on bits of tree bark, fungi and lichen. In a bit of whimsy, the groups are called “herds,” and the common name of the insects? Tree cattle. 

Stay curious!

See more of Karen’s work here.


Psocid fact sheet from Texas: Accessed 11/28/23. 

Info from the Amateur Entomologists’ Society: Accessed 11/28/23.