"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

February 12, 2010

February 12 - Nosema bombycis

Busy little Bombyx mori caterpillers happily crunch up mulberry leaves and spin cocoons where they will pupate and transform into moths. These cocoons are made of silk fibers that are harvested and processed to produce silk - in fact, 70 million pounds of silk, every year. But, of course, like virtually all creatures on the planet, silkworms suffer from parasites, too. One of the best known is Nosema bombycis, a microsproridian parasite, that causes a disease known as pébrine - so called because it produces pepper-like spots on the caterpillars. The disease is highly infectious and can pass from mother moth to her eggs, so it has long been a major concern for silkworm breeders. Louis Pasteur, the famous French microbiologist discovered that infectious agents were causing the disease in silkworms and is credited for saving the industry at the time. Microsproridia are a very diverse group of spore-forming unicellular parasites, many of which infect insects. They were once thought to be primitive eukaryotes, but they are now thought to be more closely related to fungi.

Image from this website.


  1. I have always wondered why parasites of the phylum Microsporida (no "i") are called microsporidians instead of microsporidans. It's not like we people from Canada call ourselves ... oh, wait.

  2. Nice Susan, but one point: "...once thought to be primitive eukaryotes, but they are now thought to be more closely related to fungi..." is a bit confusing. Fungi are eukaryotes too, right? "Primitive" hardly comes into it because it is a slippery idea in evolution anyway, but Microsporida were seen as being more like what in those days we called "protozoa". Last I heard they were seen as "Protoctists", but frankly, I am losing track of the latest fashions, so I am not commiting to any scheme!

  3. John,
    Thanks for the comment. That's basically what I was trying to express - that they used to be thought of as primitive eukaryotes, but now we neither use terms like primitive in evolutionary biology and we also now recognize that the microsporidians are closely related to fungi. I don't hear nor use "protoctist" anymore and we know that Protozoa are a paraphyletic group, too, but like "reptile", people know what each other mean when we say it, so it persists in the lexicon.