Body Louse from World War I
Pediculus humanus vestimenti
The body louse (pleural: lice) is a parasite of humans. Body lice are wingless insects spending their entire life on the human body and feeding exclusively on human blood. They are like head lice (Pediculus capitus), or pubic lice (Pthirus pubis), but live on the body instead. Head lice live only on the head, and pubic lice live only on the skin in the pubic area. Each type of louse is a separate species, and all look a little differently.
Infestation with body lice was very common in the trenches in WWI, with estimates of up to 97% of officers and men living in the trenches infested. Trenches were damp, cramped places, where lice thrived on the participants. They also transmitted trench fever. While not usually fatal, trench fever nevertheless took down a great many soldiers, requiring long medical treatment for recovery.
This particular specimen was collected in 1917 by John Youdale in the trenches of World War I France, during the fighting. He sent a couple of louse specimens, along with a piece of cuticle burned off his finger by the chemical warfare agent mustard gas, home to his father, William Henry Youdale. Mr. Youdale made entomology (insect) microscope slides for a living for several of the dealers around London. He had asked John to send some specimens for him to mount. This slide is one of the two body louse slides he made in 1918, and literally one of only two like this from the trenches in World War I. Mr. Youdale is pictured below at his microscope.
I was able to purchase this slide several years ago specifically for these outreach demonstrations. The slide was purchased from Mr. Brian Davidson, a member of the Quekette Microscopical Club in London. Named after a famous Victorian microscopist, Professor John Quekett, the Club was formed in 1865 is the second oldest organisation in the world dedicated to microscopy.
William Henry Youdale
Notes on Pediculus vestimenti: https://www.journals.uchicago.edu/doi/pdf/10.2307/1536721
Pediculosis page from the Centers for Disease Control (CDC): https://www.cdc.gov/dpdx/pediculosis/index.html