It was way back in 1997, within my book From Flying Toads To Snakes With Wings, when I originally documented the tragic tale of the imperial flea. In those far-distant, pre-internet days (at least for me, because at the time of my researching and writing that book I'd yet to purchase my first PC, let alone log online for the first time), I had succeeded in unearthing only a few, very sparse details concerning this entomological enigma (from an Antenna article of 1982, and even that only mentioned it in passing). Hence my coverage of it in my book was necessarily brief.
In later years, conversely, with the internet's vast, ever-growing archive of data readily available online, I have compiled a comprehensive file of additional information on this intriguing subject. This has enabled me at long last to piece together what I hope is the entire and highly (albeit unintentionally) entertaining history of the imperial flea, as well as unraveling several twisted strands of confusion and contradiction regarding this contentious creature. So here it is.
SQUASHED AND QUASHED – THE ENDING OF AN EMPEROR
It all began in Gateshead, a large town close to the city of Newcastle upon Tyne in north-west England, when one morning in early 1857 a Dr Backhouse (not Blackhouse, as occasionally claimed) woke up to find a most unwelcome, highly unexpected visitor in his bed. The visitor in question was a sizeable insect, which the good doctor lost no time in permanently dispatching, allegedly with the able assistance of one of his boots. It seemed to him to be a siphonapteran, i.e. a true flea, but one that was far bigger than any that he had ever seen before.
Hoping to learn more, Backhouse sent the flattened ex-hexapod to naturalist friend Thomas John Bold in nearby Long Benton (now Longbenton), for his opinion on what it could be. Bold, however, was unable to identify the creature, but deemed it sufficiently interesting to warrant being sent for formal examination and identification to eminent entomologist Prof. John Obadiah Westwood (1805-1893), based at Oxford University in England. So that is precisely what Bold did.
Among many other titles and academic positions, Prof. Westwood was President of the Entomological Society of London (now the Royal Entomological Society), as well as a Fellow of the Linnean Society of London. After a cursory examination of Backhouse's squashed specimen, he exhibited it during meetings held at both of these societies – a fact rarely mentioned in previous coverages of it.
The first (but only rarely alluded to) of these two meetings took place on 3 February 1857, at the Linnean Society of London; the second (much more famous) one occurred on 4 May 1857, at the Entomological Society of London. At both of them, Westwood orally described the insect as being a specimen of a hitherto-unknown species of gigantic flea, approximately 20 times as big as the common human flea Pulex irritans. Fittingly, he proposed imperator ('emperor') as the taxonomic species name for this veritable emperor among fleas.
Westwood's exhibition and naming of this specimen was duly if briefly reported as follows on p. 70 of the Proceedings of the Entomological Society of London for 1857:
Mr. Westwood also exhibited a gigantic species of flea, for which he proposed the specific name of imperator. The specimen, which is about twenty times the size of the common Pulex irritans [sic – taxonomic binomial names should always be published in italics], was found dead in a bed at Gateshead.
It was also reported (but even more briefly) as follows on p. iv of the Journal of the Proceedings of the Linnean Society, Zoology, Vol. 2 for 1858:
Read, secondly, a "Description of a new species of Pulex (P. Imperator, Westw.) found in a bedstead at Gateshead;" by J. O. Westwood, Esq., F.L.S.
Just under a fortnight following Westwood's exhibition of this specimen at the Entomological Society of London, Long Benton-based Bold confirmed in print his action that had been instrumental in bringing about this very curious creature's scientific debut. He did this by way of the following brief recollection penned on 17 May 1857 and then published shortly afterwards in the Transactions of the Tyneside Naturalists' Field Club:
Pulex Imperator [sic – the 'i' in imperator should not be capitalized], Westwood. A friend of mine [Dr Backhouse], resident in Gateshead, brought an immense flea, which he had found in his bed, for my examination. Not being able to identify it, I forwarded the creature to J.O. Westwood, Esq., by whom it has been described as new, under the above appellation, in a paper recently read before the Linnaean Society.
It is important to emphasise Bold's intermediary presence in these proceedings, because virtually every previous account of the imperial flea's history that I have read mistakenly claims that Backhouse sent the specimen directly to Westwood, rather than via Bold.
The full formal taxonomic name of any given species includes not only its binomial portion (i.e. the genus name plus the species name for that species) but also the surname of whoever formally described and named that species, plus the year in which its binomial name was first published. Consequently, it is well worth explaining here how the full formal taxonomic name of the imperial flea – Pulex imperator Westwood, 1858 – came about.
Although imperator was proposed as its species name by Westwood at both scientific society meetings where he exhibited and orally described this specimen in 1857, he did not provide at either of them a published description formally naming it as Pulex imperator. Similarly, within the brief above-quoted report published in its Proceedings for 1857 of Westwood's exhibition and oral description of this specimen at its meeting of 4 May 1857, it can be seen that the Entomological Society of London did not refer to its species as Pulex imperator either.
Conversely, in the Linnean Society of London's even briefer above-quoted report published in its own Journal of Proceedings for 1858 of Westwood's exhibition and oral description of this specimen at its 3 February 1857 meeting, it did refer to its species as Pulex imperator – which is generally deemed to be the very first time that this binomial name had appeared in print. This in turn is why the imperial flea's full scientific name contains the year 1858, rather than 1857, despite the latter year being the one in which the specimen was given the binomial name orally by Westwood. (Having said that, I cannot help but wonder why Bold's published naming of it as Pulex imperator in his 1857 Transactions of the Tyneside Naturalists' Field Club communication did not take precedence over Westwood's in 1858…?)
Anyway, taxonomic technicalities aside, there seemed no denying that Westwood's imperial flea Pulex imperator was a truly extraordinary addition to the entomological fauna of Britain and, indeed, the world, because this was unquestionably the largest flea species known to science.
So far, so good – until, that is, following his initial cursory examination that had incited him into describing and naming it as a gigantic flea, Westwood decided to conduct a much more detailed, extensive scrutiny of Backhouse's Brobdingnagian specimen. Only then was the awful truth, the embarrassing reality, of its taxonomic nature duly revealed to him.
What Westwood had originally assumed to be the creature's long, blood-sucking proboscis, a flea characteristic, turned out instead to be the basal section of a long multi-segmented antenna. Such lengthy antennae are structures conspicuous only by their absence in all bona fide fleas, whose own antennae are tiny ones that for much of the time remain concealed for their own protection within deep grooves located slightly behind the fleas' eyes. And the reason for its laterally compressed body, another flea characteristic, could now be clearly discerned as nothing more significant than the inevitable physical outcome of having been flattened side-on with considerable force by Backhouse when he struck it with his boot!
Further studies determined the tragic truth that, far from being a truly extraordinary, exceptionally large flea, the type (and only) specimen of Pulex imperator was simply a decidedly ordinary, unexceptionally-sizeable, and undeniably squashed nymph (juvenile stage) of the Oriental cockroach Blatta orientalis, a common invasive species in England.
As documented in greater detail on p. 60 within the Proceedings of the Entomological Society of London for 1859:
He [Westwood] also exhibited an insect which he had received some time previously from Mr. Backhouse, of Gateshead, as a gigantic flea, and which he had exhibited to the Society on the 4th of May 1857 (without, however, having previously had an opportunity of carefully examining it), and for which he then suggested the name of Pulex Imperator [sic]. He had, however, recently examined the insect more minutely, and had ascertained that it was a very young larva of a Blatta [sic], much distorted by being crushed flat in rather an oblique position, and with most of the limbs broken off. A small portion of the base of the multiannular antennae was visible in such a situation as to seem like a part of the mouth, but on microscopically examining it, as well as the portions of the legs still remaining, it became evident that the insect was not a flea, and on dissecting the mouth, its true character was at once detected.
[This account was also included almost verbatim within a communication concerning the imperial flea that was penned on 9 April 1894 by R. M'Lachlan of Lewisham, London, and published by the journal Entomologische Nachrichten in June 1894.]
To his credit, and in spite of the great personal shame that he must have felt, at a meeting of the Entomological Society of London held on 7 March 1859 (and attended by the afore-mentioned R. M'Lachlan among others) Westwood publicly recanted his previous pronouncements, quashing the imperial flea's taxonomic standing by unmasking its true nature as a squashed cockroach nymph (and duly documented once again in the Proceedings of the Entomological Society of London). Thus ended the brief but infamous reign of the flea realm's erroneous emperor.
Nevertheless, its crushed corpse lives on, at least in preserved state, housed in the Oxford University Museum of Natural History's very extensive Hope Entomological Collections. These were amassed by, and duly named after, English entomologist Frederick William Hope (1797-1862), who donated them to Oxford University after having founded a professorship there. Together with Westwood, he was also a founder of the Entomological Society of London in 1833.
Finally, for the sake of completeness, here is that scant little account of the imperial flea that I wrote for and included in my book From Flying Toads To Snakes With Wings more than 23 years ago, but which fired my enthusiasm for seeking out all of the additional information that I have now compiled in my much more extensive documentation above:
As for the enormous "imperial flea," formally described during the 1800s by J.O. Westwood, its only known specimen (housed in the Hope insect collections at Oxford University Museum) was later unmasked as a rather squashed juvenile Blatta orientalis – a common species of cockroach!
SUPER FLEAS AND MOUNTAIN BEAVERS
Although the imperial flea is nothing more than an imposing imposter, there really is a genuine species of giant flea out there. And despite sporting rather less prodigious proportions than those of the imperial flea, it is still more than sufficiently sizeable to claim with ease the official zoological superlative of the world's largest flea species, some specimens of which are up to one third of an inch long.
Yet, remarkably, whereas so many of its far smaller kith and kin had been known to science and the general public alike for untold centuries, this bloodsucking behemoth remained zoologically undescribed and unnamed until little more than 100 years ago.
Needless to say, such an outstanding creature readily claimed its place in all three of my volumes on new and rediscovered animals of the 20th and 21st Centuries. So here is what I wrote about it in the most recently-published tome in this trio, The Encyclopaedia of New and Rediscovered Animals: From Okapis To Onzas – And Beyond! (2012):
In 1921, publication of the formal scientific description of Hystrichopsylla schefferi introduced zoologists to the world's largest species of flea. When its original name, H. mammoth, was disallowed on a nomenclatural technicality, it was renamed H. schefferi, after its discoverer, agricultural researcher Theophilus Scheffer, from the USA's Bureau of Biological Survey. He had collected the type specimen whilst in Washington State, finding it inside a nest belonging to the world's most primitive species of rodent – Aplodontia rufa, the sewellel, though also referred to popularly but very inappropriately as the mountain beaver (it is neither a mountain-dweller nor a beaver!). Other specimens have been collected since, some of which are more than 8 mm (0.31 in) long.
Subsequently nicknamed 'Super Flea', H. schefferi appears to be a specific parasite of the sewellel; most specimens have been obtained from individuals of this rodent, or from their nests. A few have also been taken from the fur of mink and spotted skunks, but as these are carnivores that are known to prey upon sewellels it is likely that they received their over-sized parasites directly from their prey or, once again, from its nests. Little is known either about the natural history of 'Super Flea' or about that of its host, so the mystery of why the world's most primitive rodent should be exclusively parasitised by the world's largest flea has yet to be solved.
Incidentally, the taxonomic and nomenclatural niceties relating to this significant insect species are more complex than I had space to elaborate upon in my above account, so here is the full story.
What we now know to be Super Flea was initially described by American zoologist Dr Edward A. Chapin under the name Hystrichopsylla schefferi in 1919 (in a paper published by the Bulletin of the Brooklyn Entomological Society), and whose type specimen was a 6.2-mm-long female. But then in 1921, Chapin described a second, marginally bigger species, which he named H. mammoth (in a paper published by the Proceedings of the Entomological Society of Washington), and which was based upon a 7.38-mm-long male type specimen plus a 7.53-mm-long female allotype specimen, thereby making it the world's largest flea species (as it was even larger than H. schefferi). However, this latter, bigger species was later shown to be one and the same as H. schefferi.
Nevertheless, for a while it was still the rather more dramatic 1921 name H. mammoth by which Super Flea was generally referred to. Eventually, to clear up the confusion, the rules of nomenclatural priority were brought firmly into play, and as the name H. schefferi had been coined two years before H. mammoth (albeit by the same person), the latter name was disallowed (i.e. demoting it to a synonym of the former). So it is H. schefferi that is used by most (though still not all) researchers for this species today. As a result, Super Flea is nowadays technically deemed to have been described in 1919 rather than 1921, because even though the two 1921 specimens were bigger than the 1919 specimen, this is irrelevant now that the species that the 1921 specimens represented, H. mammoth, has been subsumed into H. schefferi. Who'd be a nomenclatural taxonomist?!
DINOSAUR PSEUDO-FLEAS – OR, GREATER MONSTERS HAVE LESSER MONSTERS…
The earliest known prehistoric representatives of the true fleas that possess modern morphological features are of comparably tiny size to their present-day counterparts, and date back at least 40-50 million years, having been discovered embedded in both Baltic and Dominican amber, but none dating back to Mesozoic times (65-250 million years ago) are currently known. Due to their laterally flattened bodies, these prehistoric true fleas most probably parasitized mammals and birds, just like present-day true fleas do, rather than any form of scaly reptile.
In 2012, however, Chinese scientists revealed the former existence of a hitherto-unknown lineage of prehistoric parasitic insect, unrepresented by any present-day species, whose members were considerably bigger than true fleas, whose bodies were flattened dorsoventrally rather than laterally, and which, by dating from the Jurassic and Cretacous Periods of the Mesozoic Era may well have targeted some of the mighty dinosaurs as their preferred hosts. A memorable case of greater monsters having lesser monsters upon their backs to bite them??
They were discovered independently in the same Chinese sites by two different teams of researchers and are currently known from four different species, all belonging to the specially-created genus Pseudopulex, which translates as false flea or pseudo-flea. As a result, scientists colloquially refer to these exceedingly sizeable flea analogues as pseudo-fleas, thereby emphasizing that they were not true fleas. In contrast, exhibiting their usual predilection for headline-grabbing hyperbole over sober scientific authenticity, a fair few media reports have instead burdened them with such melodramatic monikers as "monster fleas", "gigantic horror fleas", and sundry other sensationalized nicknames.
As readers who have seen such headlines but without realizing their less than accurate nature may therefore expect me to document these noteworthy insects here, I have indeed decided to do so, even though they are not true fleas, but rather because it provides an ideal opportunity to present the facts and dispel the fallacies associated with them.
The four species of pseudo-flea so far described are P. jurassicus, P. magnus, P. tanian, and P. wangi, with most scientific work so far having been conducted upon the first two species, both from China's Inner Mongolian region. As its name indicates, P. jurassicus lived during the Jurassic Period, specifically during the mid-Jurassic, approximately 165 million years ago. P. magnus, the biggest species, is of younger age, dating from the early Cretaceous, approximately 125 million years ago, P. tanian is the smallest pseudo-flea species currently known, while in P. wangi the females were much larger than the males, indicating sexual dimorphism. All four species bore longer claws on their feet than those of true fleas.
The most readily obvious morphological differences between the past and present true fleas and the exclusively prehistoric pseudo-fleas are the shape and size of their bodies. In true fleas, their body is laterally compressed, which greatly facilitates the ease of these ectoparasitic insects' movement between hairs in furry mammals and feathers in birds (and possibly in prehistoric feathered non-avian dinosaurs too) in order to reach their host's soft skin that they can then pierce with their narrow, fine proboscis and suck forth its blood, upon which they subsist.
In pseudo-fleas, conversely, their body is dorsoventrally flattened (more like those of bedbugs and lice), which, while greatly impeding these ectoparasitic insects' movement between hairs and feathers, would readily enable them to squeeze between scales, in order to reach the soft skin underneath, which they could then pierce using their broader, coarser proboscis (see below), and thence draw forth the blood that they subsisted upon.
Consequently, scientists deem it likely that whereas true fleas seek out mammals and birds as hosts, pseudo-fleas would have instead parasitized reptiles, including scaly non-avian dinosaurs, and possibly pterosaurs too.
As for body size: all of the pseudo-flea fossils so far discovered are far bigger than true fleas – measuring from 17 mm to nearly 22 mm (i.e. almost 1 inch long), whereas most true fleas are less than 6 mm long (even H. schefferi rarely reaches 8 mm long). Moreover, their mouthparts are proportionately much larger than those of true fleas, and of particular note is that their proboscis is not only broader but also serrated in a far coarser manner than the much narrower, finely-serrated proboscis of true fleas. This in turn means that when a pseudo-flea plunged its proboscis into the soft skin of its host, it is likely to have caused the pseudo-flea's dinosaurian host much more pain than the mammalian and avian hosts of true fleas experience.
In fact, to quote Oregon State University zoologist and fossil insect specialist Prof. George O. Poinar Jr speaking about pseudo-fleas in a newspaper interview from May 2012: "It would have felt about like a hypodermic needle going in – a flea shot, if not a flu shot. We can be thankful our modern fleas are not nearly this big". We can indeed!
BEE LOUSE, OIL BEETLE, AND ANOTHER WAYWARD NOTION BY WESTWOOD
I mentioned earlier in this present ShukerNature blog article of mine that Prof. J.O. Westwood lost no time in publicly conceding that he had been wrong in previously declaring the squashed remains of a juvenile cockroach to be those of a hitherto-unknown gigantic flea – but the rapidity of his recant should not really come as any great surprise. For notwithstanding his celebrated status as an entomologist of no little eminence and esteem, when it came to promoting mistaken identifications the good professor definitely had form.
In my previously-mentioned 1997 book From Flying Toads To Snakes With Wings, directly preceding my brief note concerning the imperial flea I had included the following short account concerning another erroneously-classified insect, the so-called bee louse Pediculus apis:
Equally delightful is the story of the bee louse. Its victims included among their number the very eminent eighteenth-century zoologist Johann Cristian Fabricius, who formally christened it Pediculus apis [a name that directly translates as 'bee louse']. There is no doubt that this small insect does indeed resemble a louse, but appearances can – and do – deceive. Many years later, the 'bee louse' was revealed to be the first larval stage of the oil beetle Meloë violaceus, but it is so unlike any other type of beetle larva that Fabricius can certainly be forgiven for taking its louse-like form a little too literally.
Incidentally, as a brief digression, I wish to point out here that I obtained my information concerning the bee louse's supposed scientific naming as Pediculus apis by Fabricius (1745-1808) from Ewald Reitters book Beetles (1961), which states:
Johann Cristian Fabricius (1745-1808) believed it to be a louse and named it Pediculus apis F., the bee louse.
However, I have since discovered that this name was originally given to it by none other than the originator of the taxonomic binomial system himself, a certain Carl von Linné (1707-1778), aka Carolus Linnaeus. He duly dubbed it on p. 614 in the monumental 10th edition of his pioneering work Systema Naturae, which was published in 1758 (at which time Fabricius would have only been about 13 years old).
Anyway, whereas the adult oil beetle is a notably short-winged but otherwise fairly typical glossy-black coleopteran of the free-living, non-parasitic kind commonly seen scuttling about in sunny gardens and other dry flower-nurturing habitats across Britain, continental Europe, and northern Africa, its first larval form, which hatches directly from this species' eggs, is very different morphologically, and actively parasitizes bees.
Known as a planidium, this tiny but highly specialized larva's body is long and thin (filiform), ferruginous brown in colour, very flattened dorsoventrally, and highly sclerotized, so it does indeed look superficially louse-like and entirely unlike its adult form. Moreover, each of its six limbs terminates in three long claws (as a result of which it is sometimes called a triungulin, more about which later).
Climbing up the stalk of a nearby flower in swarms and sitting in wait upon its blossom, the planidia use their claws to latch onto any bee that arrives to sip nectar and collect pollen from the flower, and these miniscule parasites are then carried by it (phoresy) back to its hive, nest, or burrow (depending upon whether the bee is a social or solitary species). Once there, the planidia duly lay waste to the bee eggs and larvae present, as well as any stored pollen, devouring them hungrily as they gradually metamorphose from one larval stage (instar) into another, until eventually they pupate into the adult beetle form, after which they then exit their apian host's domicile and live normal, non-parasitic beetle lives thereafter in the outside world.
Due to its louse-like form and the knowledge that it could be found inside bee hives, however, Linnaeus failed to make any connection between the oil beetle's planidium larva and the adult oil beetle. Instead, he mistakenly assumed that the planidium was a genuine species of louse, which, as noted earlier, he duly christened Pediculus apis, the bee louse (not to be confused, incidentally, with various highly specialized species of wingless dipteran fly, the braulids, which are colloquially dubbed bee lice because they too parasitise bees).
Nor was Linnaeus alone in this misconception – the afore-mentioned Fabricius also labored under it, as did a number of other insect authorities too, including prominent French naturalist Léon J.M. Dufour (1780-1865), who in 1828 named the bemusing little bee louse Triungulinus andrenetarum, from which the term 'triungulin', often applied to such larvae, originates. Yet another binomial name applied to this insect was Pediculus melittae, in 1802, by English entomologist William Kirby (1759-1850).
By the mid-1830s, however, it was becoming increasing accepted in entomological circles that the bee louse was actually the first larva of the oil beetle. Even so, this view was not without its skeptics, and one dissenting voice in particular was none other than that of Prof. J.O. Westwood.
In a Transactions of the Entomological Society of London paper published in 1839, which dealt with a bizarre taxonomic order of tiny parasitic insects known variously as strepsipterans, stylopids, or twisted-wings (only the males are winged, the female are both wingless and limbless), Westwood also considered the issue of bee louse/oil beetle synonymity. Yet despite acknowledging that bee lice had been directly observed emerging from oil beetle eggs, he was still not entirely convinced that the former were indeed the first larval stage of the latter. Instead, he speculated that perhaps the bee lice were of external origin and had somehow penetrated the eggs of the oil beetle, thereby giving rise when they subsequently emerged from these eggs to a misconception that they had actually originated within them:
No one, it is admitted, has ever seen the larva of Meloe, except as one of these minute Pediculi melitta, as Kirby calls them; and I have elsewhere said that, notwithstanding all the apparent proofs of their being the larvae of the Meloe, I cannot but think them in some unaccountable manner or other to be parasites, not only upon the bees, but also within the eggs of the Meloe. It is true many observers have seen them hatch from the eggs of the Meloe.
Westwood even speculated that perhaps the minute parasitic stylopids might actually be "the younger state of the Pediculus melittae". This is despite the notable fact that the stylopids belong to an entirely discrete taxonomic order from all other insect forms. Named Strepsiptera, it was created for them by none other than the afore-mentioned William Kirby, in 1813, i.e. almost 30 years before Westwood's above-quoted paper was published, so he was well aware of their taxonomic distinctness.
Happily, in 1851, distinguished English entomologist George Newport (1803-1854) revealed beyond any shadow of doubt the extraordinary life cycle of the oil beetle. For he not only had observed planidia being carried by Anthophora bees into their nest, but also had described the later, recognizably beetle larval stages in the nest's cells – and, in so doing, had thus confirmed the bee louse's true taxonomic identity.
In conclusion, the histrionic and in places quite hysterical histories of the imperial flea and the bee louse readily demonstrate that not even the most experienced experts are immune to error – but as they are, after all, only human, we should not be too surprised.
My sincere thanks go to Dr Darren J. Mann for very kindly permitting me to include his photos of the imperial flea specimen and its specimen labels within this article.