Fleas: their fans, feeding habits and the disease | Digital Collections Programme

Fleas are some of the oddest insects and sit in a strange position when it comes to how the public feel about them. Fleas are hated for their feeding activities and disease transmission whilst their aesthetics have long been admired thanks to mostly the works of Robert Hooke and his diagrams in Micrographia.

Photo showing an unfolded page insert with an illustration of a flea, in an edition of Micrographia

The illustration of a flea in Robert Hooke’s Micrographia

 

Hooke writes ‘the strength and beauty of this small creature, had it no other relation at all to man, would deserve a description’. Wonderfully phrased, this sentence sums up the feelings I have when looking at these small creatures.

At the Museum, we have an enormous collection of fleas, both pickled (in spirit in jars) and on microscope slides. It is with these slides that we have begun the most comprehensive digitisation project undertaken on fleas.

There are approximately 260,000 specimens that represent nearly 75% of the 2,600 species that have been described, including 925 primary types

A type specimen (or in some cases a group of specimens) is an example specimen on which the description and name of a new species is based.

Primary Types

Holotype is used when there is one designated type specimen.

Syntype is used if there is a type series

Lectotype is a new designated specimen in the case where the original has been lost

Secondary Types

Paratypes are secondary types in the same series.

Incredibly, at least 500 of these primary types were described by one man. In a family full of bankers, Charles Rothschild decided that fleas were his bent. His and his daughters (who also had a fondness for fleas), and Miriam Rothschild’s collection of fleas is the backbone and, arguably, most of the other body parts of the Museum’s flea collection. Digitisation of this collection and making it available to the wider scientific community on the Data Portal is vital for global scientific research on these tiny and often misunderstood specimens.

Originally described from a specimen collected off a mouse (Acomys witherbyi) in 1903, Xenopsylla cheopis is arguably one of Charles Rothschild’s most famous taxonomic endeavours. This is the Oriental rat flea and is the species incriminated as one of the major vectors that transmitted the plague.

‘A very large series of both sexes of this species was secured near Shendi in February and March, 1901. We also received a single example from Mr. W. E. de Winton, which he took from a spirit specimen of Mus gentilis, taken near Suez on the 17th of October 1900. The hosts from which the examples from Shendi were taken are Acomys Witherhyi, 3 specimens; Gerbillus robustus, 20 specimens; Arvicanthis testicularis, 20 specimens; Dipodilus Waferi, 1 specimen; Dipus jaculus, 1 specimen : Genella dongolana, 1 specimen’

Charles Rothschild’s original description.

Everyone blames the poor rat for being the major host for the flea that carried the disease but recent research has actually determined that other hosts were probably more important. As we can see from Rothschild’s original description many species were found to carry the plague flea and the one which is now thought of as the major host was the great gerbil (Rhombomys opimus).

Rothschild’s description of this flea is lacking in one important detail. He does not indicate the type series at all. So we have no knowledge of how many specimens he was referring to. He wrote a general description rather than designating either a Holotype or a Syntype series.

However, in Miriam’s catalogue of this collection she incorrectly stated that there is a Holotype for this species. The International Code for Zoological Nomenclature (IUCN) has many rules and regulations that help taxonomists with the naming of species. This problem of no designation by the original author with subsequent designation by another author is resolved in article 74.5:

74.5. Lectotype designations before 2000. In a lectotype designation made before 2000, either the term “lectotype”, or an exact translation or equivalent expression (e.g. “the type”), must have been used or the author must have unambiguously selected a particular syntype to act as the unique name-bearing type of the taxon. When the original work reveals that the taxon had been based on more than one specimen, a subsequent use of the term “holotype” does not constitute a valid lectotype designation unless the author, when wrongly using that term, explicitly indicated that he or she was selecting from the type series that particular specimen to serve as the name-bearing type.

So in this situation, one specimen has become a lectotype after the original description – and the rest of the original series have become paralectotypes.

Photograph showing the slide of the lectotype specimen, with scale bar to the right, and coloured panel to the left

The lectotype of Xenopsylla cheopis

 

Why is it important to ensure that our collection is maintained and that the information we have on it correct? And why now is it important that we disseminate this information? Well for several reasons.

As with understanding the hosts of the fleas, we also now know that it is not just this one species of flea that transmitted the plague – in fact there are at least ten species of flea that can carry the plague but there may be more.

And it is not just transmitted by fleas – two species of bedbug have been incriminated too. The lectotype, along with all of the slide collection of fleas is currently being digitised by the Digital Collections Programme.

They will be scanning the slides and the images and making these along with transcribed data available to the wider community through the Data Portal. Good images of different species will help to ensure correct identifications of existing species as well as helping establish whether there are new species.

Photograph of the drawer from above showing three columns of 4 rows of paired slides, with accompanying text labels

The Museum drawer of fleas and bugs that are all known vectors of the plague

 

And this is important as fleas are important vectors for many diseases that affects both animals and humans. In fact, there are still instances of the plague being reported across the globe. Countries considered to have a more advanced health care system such as the United States have had numerous cases and deaths reported.

Graphic showing the world in projection with black spots indicating locations of reported plague cases between 2000 and 2009. The size of the spots reflects the number of individual cases reported.

Reported plague cases by country – Source CDC

Graphic showing the USA (not including Alaska) with red dots indicating the reported cases of human plague between 1970 and 2012. The majority of the red dots are in the west of the USA.

Reported plague cases in the USA – Source CDC

By digitising our collection and enabling free access to all, researchers will have more data to produce more robust models for predicting future trends. The history of disease transmission can be mapped through our historical specimens as well as incrimination of new hosts and vectors. This will provide us with better tools in understanding the spread of diseases and how we can mitigate against it. There is so much the dead can tell us about the living!

If you enjoyed this blog post stay in touch with the flea news and the flea digitization by following @NHM_Fleas and @NHM_Digitise.