New speculative biology book about future insects

One main playing field of speculative biology concerns life somewhere else than Earth, such as my Furaha project. Another describes how life on Earth might have evolved if some event in the past had taken a different turn, such as Dougal Dixon’s book The New Dinosaurs, and the third, the subject of this post, deals with life on Earth in the future.

Well-known examples are Dixon’s After Man and the French book Demain, les animaux du futur (see posts A, B, C, D and E). While these projects discuss various animal clades, one group of animals receives less attention than it deserves, based on ecological clout, numbers of species and of individuals: insects!
  
That changed with a new speculative biology book about future insects. Before you run to the nearest bookshop, you should realise that it is in French. At the time of writing the authors do not yet know whether there will be versions in other languages. The book is called Les insectes du futur, a title that should be understandable without knowing French. The subtitle is Petite entomologie post-effondrement, which means ‘small entomology after the collapse’. The book was published last September by Belin in France. The first author is Lucas Etienne, a researcher who designed the arthropods and made the illustrations. You may already know the second author, Jean-Sébastien Steyer, as he was one of the two authors of Demain, les animaux du futur ; he is a palaeontologist (see his book Earth before the dinosaurs) and has published various books popularising science. 

The book counts 163 pages and describes a large variety of insects and other arthropods, as told by two human researchers who make their way from Paris to Monaco in the year 2499. The protagonists make this journey after leaving the underground collection rooms of the Muséum d’Histoire naturelle where they sat out a nuclear war. They encounter many species of arthropods that are as new to them as they are to the reader. The book is divided into chapters that describe ecosystems and various biological principles, such as camouflage, symbiosis, parasitism, flight and adaptations to aquatic life. Let’s have a look at a few organisms.

Click to enlarge; © Belin Éditeur/Humensis, 2025

Nepa dendrobates
This animal may look like a tropical frog, but it is in fact an insect of the clade Hemiptera. The bright dazzling colours of the frog it mimics are a warning to would-be predators that these frogs are poisonous. The insect mimics the frog in colour and shape, so predators should mistake the tasty insect for a poisonous frog and stay clear. This is a nice example of Batesian mimicry, something than can be described as a sheep in wolf’s clothing. I wondered what happens if some predator that never eats frogs comes across such an insect. That predator would not be warned off by the colours because it never eats frogs, poisonous or otherwise. It would still not eat the insect as it wouldn’t recognise the insect as an insect, but as something inedible. Does that turn the effect into simple camouflage rather then Batesian mimicry? That sounds like a nice subject for a biology examination.

Click to enlarge; © Belin Éditeur/Humensis, 2025

Aquatic ants
Quite a few insects adapted to a life underwater, but never ants, or so I thought. I was wrong: there is an ant that dives into the fluid of pitcher plants to steal animals that fell in, and there is a mangrove species that allows its nest to be inundated by the tide. Etienne and Steyer developed their own aquatic ants. They developed gills, have grown considerably larger than any terrestrial ant and have become good swimmers. These ants are still colonial and still build their own housing, which in this case resulting in underwater ant cities. These marine ants developed symbiosis with corals, which is a very interesting idea, so altogether they paint a very intriguing picture.

Click to enlarge; © Belin Éditeur/Humensis, 2025

Abyssal wasp
This wasp descendant can grow to an astonishing length of 60 centimetres. It is bioluminescent thanks to symbiosis with luminescent bacteria. Unfortunately, the book provides little detail how it lives, although it is clear that it has lost its sting.

The story takes place in the year 2499, almost 500 years from now. That may be long enough for mankind to further change the climate and to damage or destroy many ecosystems, bringing about an overall collapse. But how much biological evolution can take place in that time? In other words, what is the maximum speed of evolution? That is probably complex. Factors that must play a role are how large the pressure to change is, such as due to a quickly changing environment and mixing species that were previously separated. The amount of genetic variability and the mutation rate would also be important modifiers of change. The morphological changes in the insect book are so large in such a short time that evolution here has jumped, something known as ‘saltation’.

One theory of saltational evolution by Goldschmidt described ‘hopeful monsters’ that came about through very large mutations, large enough to explain the advent of new species. This concept of saltational evolution was never wholly discarded and new papers keep on appearing on the subject. I do not know enough about it and cannot therefore afford a strong opinion on the matter. Readers of this blog will know about ‘punctuated equilibrium’, a theory stating that species do not change for a long time but may then suddenly undergo a major change. At present, there is evidence for both long periods of stasis as well as for evolutionary jumps. In short, the speed of evolution can vary. 

But the future insect book still forces a closer look at that speed. The fossil record does not exactly have a nice temporal resolution, with a complete fossil every hundred generations or so.

 

Click to enlarge; source: wikipedia

This Wikipedia graph neatly explains that gradual change over 10,000 years will show up as a qualitative jump if you only sample the record once every 10,000 years. But the graph is quite hypothetical. Very well, let’s hypothesise a bit ourselves. Making an insect look like a frog must involve changes to a great many genes. It seems extremely unlikely for all genes involved to mutate in the correct direction at the same time (but if this does happen, you might get an evolutionary jump). It seems more likely that weeding out any variant that reduces ‘frogginess’ requires untold encounters between predators, the insect and the frog. How many generations would that take? Likewise, adapting insects to water is likely to go through successive stages, perhaps starting with short dips to get food. From there, you can expect changes allowing the animal to last longer under water. I would not be surprised that breeding under water would be one of the last changes to take place. Again, it seems unlikely that all features would change in the correct direction at the same time.          
  
I understand the style figure of using human guides to show these new animals. The alternative would have been to move forward a few million years and to depict the animals as they are, without human interest. Would that have been better? That depends on what you want from such a book. The authors must have had great fun using their new arthropods to illustrate various biological principles such as Batesian mimicry. They did not in fact use the term Batesian mimicry; instead, they chose to teach by example, making their book highly accessible. That is an advantage and does not harm the fun. Come to think of it, showing how biology works is, for me, the essence of why speculative biology is fun.

From erect dinosaurs to pivoting fly feet (Frustrating feet 2)

This post is long, fairly complicated and rambles along a bit, so do not say I did not warn you. We are so used to seeing big mammals that most ‘alien’ legs in drawings and films are just mammal legs. One thing you will find in many books is that a key feature of mammal locomotion is that the legs are 'erect'. 

 

Click to enlarge. From Box 4.3 in: Fastovsky & Weishampel. Dinosurs A concise natural history. Fourth Edition Cambridge University Press 2021

 

The image above shows such a scheme, making the point that dinosaurs legs are as erect as mammal legs, using a human as an example. I have always felt that the legs of the dinosaur in the picture are not really 'erect', while the human's leg both are less erect than they usually are in a standing human. 

Click to enlarge; copyright Gert van Dijk

Let's explore this further. Above, you see the species Disniformis inexpectus and on the left its cousin, D. expectus. The elbows and knees of D. inexpectus stick out sideways, while those of D. expectus do not. Which animal stands in the most energy-efficient way, and which is the most 'erect'?

 <pause to think>

Many readers may feel that D. expectus wins on both accounts. But have a closer look: in both animals the feet are placed precisely underneath the hips, and the leg segments are tilted in opposite directions as you move down. Because the joints are angled, energy has to be spent to keep these joints from bending further under the influence of gravity. How much energy depends on the angle of the joints and how far these joints are situated from the vertical line connecting hips and feet. Guess what: the legs and joints angles are exactly the same. The legs were just rotated, except for the feet, so exactly the same amount of energy is needed to keep the joints stable.

Personally, I would call a leg fully 'erect' only if the segments are all vertical, as they largely are in standing elephants (and standing people!). If all segments are fully erect, the feet must end up directly underneath the hips. In the dinosaurs and both species of Disniformis, the feet are also placed directly underneath the hips, and it seems some authors use the word 'erect' to mean only that aspect. The opposite of 'feet underneath hips' (FUH) must be 'feet away from hips' (FAFH). If the feet are placed well to the side of the animal, you get a sprawling stance, like salamanders and insects use.         

Perhaps you feel that all this changes when the species start to walk, and then we will see that D. inexpectus can only plod along while D. expectus trots elegantly out of sight. Not so! The legs of both species can extend to the same length and the joints move through the same arcs. This means that  elbows and knees can be kept close to the centre of the animal regardless of whether they deviate to the inside, outside, back or front.

 

Click to enlarge; copyright Gert van Dijk

Still, D. expectus will have a gait advantage in that its joints can be designed much simpler than in D. inexpectus. The dinosaur drawing and the reworked D. expectus above show simple hinge joints that allow the legs to move only in a fore-and-aft direction. That save energy; nice, right?

It would be nice if animals were like trains, only moving along predefined linear tracks. But they also need to turn and to step sideways and do other things beside walking in a straight line. An animal must be able to move its feet fore and aft, but also to the side, and must also be able to turn toes in or out. This requires rotation along all three axes. You can be creative and appoint different movements to different joints, but iff you wish to obtain the largest reach for the foot, you should give the hip joint the most freedom. That is probably the reason mammal hips have ball joints (and dinosaur hips too, as far as I know). My guess is that the most proximal joints (hips/shoulders) in alien animals will also have three axes of rotation. Mind you, the three axes do not have to be used to the same degree in daily life (fore-aft movements will see more use than toe in/out movement).

The ankle joint should allow the foot to adapt to uneven ground, so the joint must allow a toe up/down rotation and also a thumb up/down rotation. That is two axes already; we will get back to the third axis. This leaves joints in between, and these need only have one direction of rotation, like mammal knees (that need not be universal though and is probably something for another post).

 

Click to enlarge; copyright Gert van Dijk

We are now getting to something that has vexed me for years. Above is an image from a post from 2010, showing D. salamandris. This is what I wrote at the time: "To get a movement suitable for walking, its foot should move in a straight line from front to aft … But ensuring that the foot always points forwards also requires that there is a way to rotate some of the bones around a longitudinal axis."

It is the need for that third rotational movement in animals with FAFH ('sprawling') legs that vexes me. Humans are very good at this movement, called pronation and supination (if you hold your arm in front of you, turning the palm down is pronation and turning it up is supination). But I couldn’t find good discussions on this type of movement in the prototypical sprawlers: arthropods. If readers know about such studies, please let me know.

I looked at some internet videos of walking insects to see whether their feet remained fixed to the surface while the leg rotated; if so, these insects had pro- and supination. I would expect the tarsus to allow that movement, even though the text I found previously said that the tarsus only allowed flexion and extension. If the foot would rotate along with the leg, it would pivot over the ground, something hardly compatible with a firm grip.

There weren't that many videos that allowed such close scrutiny, but here is one, showing a fly walking across glass. The foot stays in largely the same position and does not rotate along with the leg. To allow it to that while the hip is moving forward, something has to 'bend'. The tarsus indeed seems to bend a bit, but not much. In fact, the tarsus keeps on pointing in the same direction all the time. 

 

Click to enlarge; copyright Gert van Dijk

I thought of a possible explanation, and it involves a different kind of hip movement. Above are two spidrids. The first has a typical vertical axis of rotation through the hip; that's a normal spidrid. The rest of the leg lies in a plane, and the movement is shown by two 'ghost legs' (this is typically how crabs move). The second image has another hip, with the axis horizontal. The animal can still reach fore and aft, but the results looks different.

 

Here is what the differences amount in an animated view: first a typical spidrid movement with a vertical axis. The gray structures indicate the planes in which the legs move.

 

And now a Neospidrid with a horizontal axis (the model caters for intermediate angles too).

An thay means we can get back to flies; in a textbook of arthropod anatomy (Manton 1977) I found indications that insects hips have an added 'rocking' movement that would indeed allow some rotation around a horizontal axis. But there's a rub. With such an axis, you still need pro- and supination to keep the insect's 'palm' against the surface. I still do not know how insects solve the need for this longitudinal foot movements. Crabs are probably easier, as they have no feet in the common sense, so they can just pivot on the tips of their legs. 

I confess that designing alien animals is sometimes easier than studying Earth animals. In particular when it comes to feet!