The birth of a curious mind – Robert Hooke | Curator of Diptera

Today’s blog is in honour of the great microscopist Robert Hooke. Born on 18 July 1685 (which is actually the 28 July today due to the shift to the Gregorian calendar in Britain in 1752), Robert Hooke – although not as famous as some of his counterparts such as Sir Christopher Wren and Sir Isaac Newton – was to have a huge impact on the scientific community. He was a curious individual, always observing, noting, and drawing what he saw. This drive and curiosity resulted in this ‘caulkhead’ (native of the Isle of Wight, UK) producing in 1665 at the tender age of 30 years, one of my favorite books – ‘Micrographia or Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses with Observations and Inquiries thereupon’.

Photo showing the cover of Erica's copy of Micrographia
My very own copy of the great book Micrographia

Not the snappiest of subtitles, I concur, but contained within the pages of this book are some of the earliest but arguably still scientifically important drawings/diagrams of life as seen under a microscope.

Hooke had such a good mechanical knowledge and understanding of the effects of lens on magnification that he could produce stunningly accurate drawings that are still valid today. Some would argue that this is one of the most important scientific books ever published!

Hooke’s work wasn’t the first to show life down a lens but the level of precision seen in his work was a level far greater than what had been before.

As a Dipterist, I was more than impressed with this tome as so many of his drawings were those of flies and their body parts including the fold out diagram or schema of the eyes of a hoverfly.

Photo showing the close-up drawing of the eyes across a two page spread.
The eyes of a dronefly (Syrphidae)


However, in this blog I want to talk about a different insect. Probably the most famous fold out drawing in this book is the flea and definitely the largest. I am lucky to own a copy that is a faithful reprint of the original and so my flea is a flip out drawing just as the original one was.

Photo showing the unfolded pages containing the drawing of a flea as observed from the side.
The fold out drawing of the flea

Although the drawings were brilliant, Hooke never actually stated what species they were. However, that is unsurprising if you consider the book was published in 1665. It would be another hundred years before Carl Linnaeus would first describe this species.

It is commonly (although slightly misleadingly) thought to be the human flea (Pulex irritans). There is also the possibility that it may have been the oriental rat flea (Xenopsylla cheopis).  During the time Hooke was writing, both species would have been present in London, where he was based. 1665 is more famous for another phenomenon that was sweeping across the UK – the deadly plague. The scientific community and public could, therefore, for the first time see clearly the vectors (carriers) of this deadly disease. However, as more specialists believe Hooke’s drawing to refer to the former species than the latter, I shall concentrate on that one.

Pulex irritans should perhaps be known as the cosmopolitan flea as they have a large variety of hosts alongside humans including: cats, dogs, bats, rats, pigs and chickens! By having such a smorgasbord to feed upon they have been able to spread across the globe. This has caused problems with identification, and as this species can – and does – transmit the plague, this is of medical importance.

When Linnaeus described this species he either did not keep a type specimen, (the specimen upon which the description of the species is based) or it was subsequently lost. Linnaeus was also not one to provide diagrams for the species that he described.

Sadly, this has led to much confusion about the species. In fact, a Neotype (the designation of a new specimen to be used as the exemplar of the species when the original has been lost or is missing) was only designated in 1958 – this was 300 years after the original description – by Franciscus Smit, the custodian of the Rothschild flea collection from 1950 to 1983.

Photo of the slide with the flea in a yellow, circular middle section with red, square labels to the left and right on the glass.
Neotype slide of Pulex irritans from the Rothschild Collection at the Museum

Today, we recognise that 5 synonyms of this species, some of which may not actually be true synonyms but are valid species in their own right. One such issue was with Pulex simulans which was originally described back in 1895 by Baker, who later went on to demote this species to a synonym of P. irritans. Smit wrote in 1958 that the situation was ‘deplorable that the differences between the two species concerned have not been elucidated before…’ And this species has now been promoted once more to be a valid one.

And why should this concern us? Well Pulex simulans is a better carrier of the plague due to it living on smaller mammals that act as reserviors for this disease whereas Pulex irritans does not.  Many specimens therefore may have been misidentified in the past and this would affect our knowledge of the diseases’ true spread.

Today though, thanks to people like Hooke who really tinkered and played with lenses, there has been an explosion in microscopes and imaging equipment. Here at the Museum we are undertaking a huge digitisation project to get lots of images and data about the Rothschild Collection (within which the Neotype is housed) out to the public via our Data Portal.

Photo showing the microscope image of the flea, with its head to the left and abdomen to the right. The body is translucent and the legs hang below.
A high resolution image of whole body of Pulex irritans that will be available on the Museum’s Data Portal

By providing high resolution images and all associated data, our specimens can help researchers globally to quickly access and check the identification of their specimens. Within the next year, we plan to have at least 30,000 slides – like those pictured here – imaged and available on the portal. The importance of these specimens is vast due to their impact as carriers of disease.

So, a big happy birthday and thank you to Robert Hooke – ‘for he’s a jolly good fellow…’

And if you’d like to keep in touch with the world of fleas, follow @NHM_Fleas on Twitter.

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