The Flea Song

The Flea Song

Today I gave the “entomological interlude” during a talk about Ludwig van Beethoven‘s arrangement of Johann Wolfgang Goethe‘s poem “Flohlied” which is a part of “Faust“. The seminar was part of a Cultual Creativity series through the Musicology Division at the University of Illinois. (NB: I am that person who can not read music, yet can recognize Beethoven’s 9th Symphony as the “Die Hard” theme song.)

Das Flohlied (Flea Song) is part of the scene “Auerbach’s Cellar in Leipzig” in Faust I (First published around 1790). The song is about a king who loved a flea on which he lavished many riches. The flea is fitted with fine clothing and is made Head of State. The flea’s family members are also awarded high positions in the government. The other members of the King’s court did not dare speak up and complain. Instead they tried to cope with the biting and the itching, but what they really wanted to do was kill the little critters.

William Kinderman presented a talk on the political satire conveyed by Beethoven in the composers correspondence and in his work around the time Beethoven wrote the music for the Flea Song. For the performance Prof. Kinderman was joined by tenor Jerold Siena.

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I was to provide a little bit of background about the life history of fleas – the entomological interlude. There is much to tell about fleas, but I only had 10 minutes, and was speaking to a non-science audience that was there for the music. But I felt up for the challenge!

I decided to have Goethe’s words dictate the organization of the presentation. Below are my slides, the translation of the poem and my notes.

Slide01

Thank you very much for inviting me to give a little bit of background about fleas and help you connect this insect with both Goethe and Beethoven. (As an aside: This is an iconic drawing of a flea by Robert Hooke from his 1665 book Micrographia, which can be viewed here on the campus of the University of Illinois at the Rare Books and Manuscripts Library)

Slide02A king there was once reigning,
  Who had a goodly flea,
  Him loved he without feigning,
  As his own son were he!

Lets picture ourselves in late 18th Century Western-Europe. Goethe opens das FlohLied, with a description of a King actually being quite fond of a flea. We may consider that odd, and of course it is, but I think it is important to keep in mind that at that time society viewed ectoparasites such as fleas, lice, ticks and bedbugs more favorably, merely as a nuisance. This view of ectoparasites did not really change until the mid-19th Century when it was discovered that arthropods such as mosquitoes could vector horrible diseases. And not until about 1900 was it known that fleas vectored the bacterium that causes the plague.

In other words, a poem or song about a highly regarded flea is not as strange in 1760 as it may seem now.

Slide03Some basic facts about fleas. Fleas are very small. The body of the flea is about 3mm long. Fleas belong to the insect order Siphonaptera, and there are about 2600 described species of fleas. Adult fleas feed on the blood of their mammalian or avian hosts. Only about a handful of the flea species live in close association with humans, and can use humans as a host but none are specialized on humans.

Fleas do not have wings, they are famous for their ability to jump – they have specialized legs. They have also physiological adaptations that help in dispersal. For instance, fleas are able, through the bloodmeal, to determine when a host rabbit is pregnant. In response female fleas will then start producing eggs. As soon as the baby rabbits are born, the female fleas make their way down to them and once on board they start feeding and laying eggs. After 12 days, the adult fleas make their way back to the mother. They complete this mini-migration every time the mother rabbit gives birth. So they don’t have to be able to fly or even jump very far to be able to disperse their offspring.

Slide04His tailor then he summon’d, 
  The tailor to him goes;
  Now measure me the youngster
  For jerkin and for hose!

In the Flea Song the King calls upon dressmakers to make clothing for the fleas. Funny concept, of course, but not really that odd for that time period.

Around the time that Goethe wrote das FlohLied watchmakers tried to harness fleas, with tiny gold wires, to demonstrate their skills in fine manipulation.

In other parts of the world people also dressed up fleas. In Mexico there is a tradition of Pulgas Vestidas, where fleas are dressed and painted to represent people – such as brides and grooms. They are very very small – and probably only contain the head of the flea.

Slide05In satin and in velvet 
  Behold the younker dressed;
  Bedizen’d o’er with ribbons,
  A cross upon his breast.
Prime minister they made him, 
  He wore a star of state;
  And all his poor relations
  Were courtiers, rich and great.

The late 18th century was the start of the flea circus mania in Europe. It is not clear to me if by 1790 this had reached Germany. But it again shows how enamored people (including the King) were with fleas. This is a picture from the famous flea circus in Copenhagen’s Tivoli Gardens, which was open until the mid 1960s. Fleas would be caught and rigged up in a harness made of thin gold wires. These harnesses could then be attached to props. Fleas were made to pull relatively large objects. Or they were given a ball to juggle or kick. [Video]

Slide06The gentlemen and ladies 
  At court were sore distressed;
  The queen and all her maidens
  Were bitten by the pest,
And yet they dared not scratch them, 
  Or chase the fleas away.

In the poem Goethe mentions that the people at the King’s court are getting bit and that the bites start to get itchy.

This is a very good description of a flea bite. Fleas bite…and they suck!

They have mouthparts, that are basically a pair of sharp lancets with serrated edges and a hard, sharp, awl-like instrument. They make a puncture in the skin, opening up blood vessels, and then suck up the blood by creating a tube with their mouthparts.

The flea’s saliva may cause an allergic reaction that results in welts and itching. It is the itching that usually sends people to the doctor and pets to the vet.

Slide07As Professor Kinderman explained the representation of the flea’s jump is obvious in Beethoven’s music. The flea’s jump is an almost unbelievably fast, precise, and reliable motion.

Fleas can jump about 200 times their own body-length. The jump happens so fast that only about 5 years ago the high-speed camera technology was sophisticated enough to capture the jump in such a way that it could conclusively be shown what parts of the leg a flea uses to jump. [Video]

Slide08The energy for a flea leap comes from a spring inside the flea’s leg. This spring stores and then releases the energy needed to jump. Fleas first lock the joint between body and hind leg, and then they contract muscles within the body. This muscle contraction compresses part of the exoskeleton of the flea, most importantly a part of the body that contains the elastic protein resilin. So in the end, not just the muscle, but also the relatively rigid exoskeleton acts as a tensed spring. The lock on the hind legs is then released, and the rapid expansion of the spring releases the stored energy. The forces in the spring are transmitted through the leg, through the feet, to the ground, which propels the jump.

The resilin material is very interesting since it is very resilient, far more so than rubber we use in engineered devices. The flea can repeat this jump many times without suffering material fatigue.

Slide09This brings me to the all important insect cuticle, or exoskeleton. Insects do not have a skeletal system like we do. Insects are covered with this, at least in my eyes, amazing material, made from pretty simple building blocks, that, depending on the species and life stage of the insect, can be hard (think of a beetle) or soft (think of a caterpillar).

In this picture you can see that the cuticle of the flea is divided up into different segments, and that it may have some sensory hairs and glands – so it is not completely one rigid structure. This makes movement and interaction with the environment easier despite having an exoskeleton.

The cuticle is arranged hierarchically, and built from the bottom up – at atmospheric pressure and moderate ambient temperature – using materials that are readily available in nature. This manufacturing technique is not common in human manufacturing when we use lots of pressure, and heat, and nasty chemicals.

The cuticle is made up of different layers and these layers may not line up perfectly. This is a good thing. Sometimes a crack may appear but not be propagated further down, because the different hierarchical layers “stop” the crack. Again, we do no really engineer our materials with this level of resiliency.

(For more detail about the insect cuticle see posts on this blog here, here and here)

Of course, that fleas have such an amazing exoskeleton also has disadvantages…

Slide10If we are bit, we catch them
  And crack them without delay.

You can’t just squash a flea. Similar to bubble wrap if you push on a flea it compresses, it does not pop.

Since the flea’s cuticle is also made up of these different layers, and the layers are not very stiff it makes it that fleas are very difficult to kill. You cannot just step on them, stomp them, or crush them. You actually have to puncture the cuticle, maybe with your nails, and then bend them until they snap – “KNICKEN” as Goethe called it.

And then if you hold your finger on the flea you can also suffocate it “ERSTICKEN”, but this will not be so easy since fleas have multiple entry points for air (not just the mouth area as in mammals).

(Actually the best way to kill a flee is by rubbing it between your fingers so that the legs fall off…then it will not be able to find a new host and continue feeding

Slide11At the risk of going slightly off topic here I want to point out that much of the research done on fleas during the twentieth century was done by Dame Miriam Rothschild. Yes, she was a member of the famous bankers family. Miriam had become interested in fleas because her father Charles had started an impressive flea collection, and her uncle Walter a Natural History Museum.

Miriam was the one who first described the endocrine regulation of reproduction in fleas, as I described, and was also the driving force behind figuring out how fleas jump – the biomechanics of the jump.

I cannot resist these wonderfully inspiring pictures of Rothschild in her (privately funded) lab with her children. She certainly is an inspiration to female scientists like myself.

Thank you so much for giving me the opportunity to share the wonderful lives of fleas with you.

Slide12FleaSongFlyer (Art work by Nils Cordes)

Jump! Go Ahead, Jump, Little Springtail.

Jump! Go Ahead, Jump, Little Springtail.

And here it is. Behold the best blog-banner ever – created by Nils Cordes*! 

Of course, the premiere of such a great banner also requires a blog post that explains it. So let me try.

The animal featured in this blog’s banner is a springtail from the hexapod lineage Collembola. Collembola are not insects but entomologists are an inclusive bunch so we gladly incorporate spiders and entognathous creatures into our studies and teachings.

Springtails are very likely the most abundant arthropods on earth. They occur in the soil (different species at different depths), in leaf litter, moss, under logs, etc. One of the most distinguishing features, if you can consider anything on an animal that is only 0.12 to 17 mm long distinguishing, is the forked furca at the posterior end of the animal. The furca is present in a lot of species, but not all. Those that live deeper in the soil usually lack the structure because they do not need it since its main function is for jumping.

CollembolaBoth

Generalized “elongate” (top) and “globular” (bottom) Collembola. Furca (springing mechanism) in red – the springtail at the top has the mechanism partly retracted and the springtail in the bottom picture has the furca extended. (Marianne Alleyne)

Collembola species can have varying body shapes, but generally there are those with elongated bodies and those with more globular bodies. Collembola can walk, run and climb, but the locomotory specialty that they are best known for (and which seems to be rather ancestral) is jumping.

Globular Springtail Dicyrtomina saundersi. Body length = 1.7mm. Picture by Lord V. Used with permission.

Globular springtail Dicyrtomina saundersi. Body length = 1.7mm. Picture by Lord V. (Used with permission.)

Picture by Lord V. Used with permission.

Elongate springtail. Body length = 2.3 mm. Picture by Lord V. (Used with permission.)

This excellent picture by Lord V is of a picture walking over a glass slide. Clearly visible is the forked furca that can prope the springtail into the air.

This excellent picture is of a springtail’s underbelly. The picture was taken by Lord V as a springtail walked over a glass slide. Clearly visible is the forked furca that can propel the animal into the air. (Used with permission.)

Collembola can jump multiple times in a row, those with globular bodies and more advanced tracheal systems more often (1). In general, springtails tire easily so that jumping is usually only used as an escape mechanism. The jump can take the animal in any direction. Since the furca is located at the extremity of the body, directly beneath the center of gravity, the dynamics of the jump cause the body to rotate head over end. Some Collembola species can jump very high, others take a shallower trajectory but land far away from point of takeoff.

This jumping escape response is quite successful but it does require modifications of the entire body plan. The cuticle, the (hydrostatic) endoskeleton, tendons, and muscles all work together to manipulate the body in such a way that the propulsion is optimal.  How exactly this happens is not very well understood, yet this system holds inspirational lessons for passively compliant locomotory structures.

At rest the furca is held within a ventral groove of the abdomen. At the time of the jump the furca moves from this resting (retracted) position to the extended position. Based on morphological and kinematic observations (there is no direct experimental evidence) it appears that as the furca moves it compresses a “spring”. After it passes a critical point of extension the spring releases all the energy, which in turn causes the springing organ to snap out at high speed. If this happens as the springing organ hits a substrate a force is created that propels the animal upward.

The springing mechanism of a generalized springtail; partially retracted (left) and extended (right).

The springing mechanism of a generalized springtail; partially retracted (left) and extended (right). (Marianne Alleyne)

What exactly comprises this “spring” is not clear. Earliest experiments done by Manton (2) in the early 1970s concluded that to evert the springing organ the body’s hydraulics (pressure on the fluid that makes up most of inside of the body = hemocoel) was important. However, later in the 1970s, Christian (3) concluded that direct muscle action, and not necessarily hydraulics, was the main force inducer. In the 1990s, when high-speed photography had advanced greatly, Brackenbury and Hunt (4) concluded from their experiments that hydraulic forces created by pressurizing the hemocoel increases tension on abdominal sclerites (the exoskeletal plates) that results in a click mechanism that propels the animal into the air. All these studies do agree that elastic elements within the base of the springing organ and within the exoskeleton, as well as the body as whole, are important too. To what extent is not known.

Click mechanism model of the furca. The furca, at rest, is retracted into an abdominal ventral groove. A pair of "basal rods" (springs) are embedded in ventral and lateral parts of the abdominal sclerites 4 & 5, these springs also attach to the apex of the furca. The spring/click mechanism gets help from muscle and active dorsiflexion of the body, which both help release to spring organ from the groove)

Click mechanism model of the furca (red) and distal end of abdomen. The furca, at rest, is retracted into an abdominal ventral groove. A pair of “basal rods” (springs, in blue) are embedded in ventral and lateral parts of the abdominal sclerites 4 & 5, these springs also attach to the apex of the furca. The spring/click mechanism gets help from muscle and active dorsiflexion of the body (in orange), to release the spring organ from the groove. After the furca passes a critical point of extension the spring releases all the energy. (Drawing by Marianne Alleyne based on Brackenbury & Hunt, 1993)

Imagine a beam or a chopstick that’s flexible transversally but somewhat stiff longitudinally. If you compress it, it doesn’t change…up to a point. Then it ‘snaps’ out and buckles. You get a rapid displacement as all the strain energy is released. The exoskeleton of the springtail does a similar thing. It stores the strain energy and then goes through a snap-through buckling phenomenon to produce large strain motion which is then amplified by the tail and presto…springtail in motion.

Many insects, and other animals, use musculoskeletal springs that are incorporated into the complete body plan.  These springs help achieve a high rate of acceleration, or a further jumping distance, and help save metabolic energy. Based on these findings compliant structures and materials have been incorporated into bioinspired legged robots (5). Compliant legged robots achieve a few important things: increased energy efficiency, increased speed, ability to avoid obstacles (in case of jumping robots), and the ability to use more simplified controls to enable enhanced gait control and shock absorption. Springs in bioinspired robots have used elements such as airsprings (e.g. compressed air) and compliant materials, but improvement is still possible. Airsprings, for instance, are not very efficient because they end up converting much of the energy they store into heat. In addition, some of the compliant materials are better than others. Rubbery materials, like elastomers, tend to have a fair bit of viscosity in them and so some (maybe lots) of the energy that it stores is lost to heat as well. For high efficiency, most robotic-type systems currently use mechanical springs (i.e. metals). Bioinspired robots also incorporate series elastic actuators that have linear springs intentionally placed in series between the motor and actuator output, which results in the actuator being bulky.

The variety of jumping mechanisms among insects is great (think: click beetle, flea, grasshoppers, treehoppers, etc.). The intriguing aspect of the jumping mechanism in springtails is that it operates so efficiently at a very small scale, much smaller than any bioinspired robot that has been developed. In the future we will be able to manufacture almost microscopic devices incorporating different characteristics into small structures using “springs” and compliant materials.

Maybe we can incorporate locomotory mechanisms that propel the object, using very little energy. Inspiration for what materials to use and how to construct the object can be found through further study of the springtail’s click mechanism. Somewhat surprisingly not much research has been published on this system since the 1990s. Yet with help from today’s high-speed cameras and microscopy techniques we should be better able to understand how the springtail propels itself. Advanced computer aided engineering (CAE) tools, like finite element analysis (FEA), could be used to augment the visual data and elicit some fundamental internal characteristics that are not visibly detectable.

By researching this topic I thought of a few applications for technologies based on the Collembola’s spring mechanisms. Click mechanisms at the scale of a springtail’s springing mechanism could possibly aid stent design or inspire development of other deployable structures that snap open or closed based on certain environmental conditions. Maybe small springing mechanisms can be incorporated in groups and serve as strain sensors on bigger structures. And who wouldn’t welcome millimeter-sized robots that can perform in a futuristic “flea circus”?

PLEASE LEAVE A COMMENT (OR CONTACT ME VIA TWITTER @COTESIA1) IF YOU HAVE ANY NOVEL IDEAS FOR A SPRINGTAIL INSPIRED JUMPING MECHANISM. JUST IMAGINE.

REFERENCES:

(1) B. Ruhfus and D. Zinkler, Investigations on the sources utilized for the energy supply fueling the jump of springtails, Journal of Insect Physiology, Volume 41, Issue 4, April 1995, Pages 297-301, ISSN 0022-1910, 10.1016/0022-1910(94)00122-W.

(2) S. M. Manton. The Arthropoda: Habits, functional morphology, and evolution. Clarendon Press, Oxford, 1977. ISBN: 019857391X

(3) E. Christian. The jump of the springtails. Naturwissenschaften, Volume 65, Issue 9, 1978, Pages 495-496, 10.1007/BF00702849

(4) J. Brackenbury and H. Hunt. Jumping in springtails: mechanism and dynamics. Journal of Zoology, Volume 229, Issue 2, 1993, Pages 217-236, ISSN 1469-7998, 10.1111/j.1469-7998.1993.tb02632.x

(5) Z. Zhou and S. Bi. A survey of bio-inspired compliant legged robot designs. Bioinspiration and Biomimetics,Volume 7, Issue 4, 2012, 20 pages 10.1088/1748-3182/7/4/041001

SPRINGTAIL RESOURCES:

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*My friends can attest to the fact that I have been talking for a long, long time about starting a blog about how we can use insects to inspire new technologies. One of these friends who had to humor me for so long is Nils Cordes. I met Nils when he was a student at Illinois, but he is currently finishing up his PhD at the University of Bielefeld in Germany. Nils is a great scientist, and a great communicator. He is also a wonderful artist. He offered, those many years ago, to create some art work for this (then still imaginary) blog that I was going to use to communicate my love of insects. And he did…behold the best blog banner EVAH!