One problem, many solutions: how insects evolved into predators
The praying mantis looks like a hunting machine: it waits motionless for its prey, then snatches it up in a flash with its front legs, which act as traps. But the most interesting thing is that evolution has created similar ‘trapping’ limbs in insects on more than one occasion.
A new study shows that prehensile forelimbs evolved independently in different groups of insects at least seven times. Yet evolution has never arrived at a single ‘ideal’ predator design. Different lineages solved the same problem — catching prey — in different ways.
The study by researchers at Kobe University has been published in *Scientific Reports*.
Details
In many insects, the forelegs are used for walking. But in mantises and a number of other predatory groups, they have evolved into weapons: the limbs fold in, grasp the prey and hold it in place whilst the insect feeds.
Such limbs are referred to as grasping, catching or predatory forelegs. In the scientific literature, they are described as adaptations for striking and seizing prey; they are considered one of the most striking examples of possible convergent evolution in insects.
Convergent evolution is when different animals independently arrive at similar solutions. A classic example: sharks, dolphins and ichthyosaurs are not closely related, but they all had a streamlined body shape adapted for life in water. In the case of insects, grasping legs have long been considered a similar example.
But a team from Kobe University decided to investigate: have different predatory insects really evolved the same form, or does it merely seem to us that their legs are similar?
How the scientists tested this
The researchers constructed a sort of ‘shape map’. They compared the lengths of different body parts and limbs in insects with conventional forelegs and in those with grasping legs.
In doing so, the scientists deliberately avoided delving into the finer details of anatomy — spines, serrations, the shape of joints and other features. They looked at the overall body architecture: how proportions change when forelegs are transformed into hunting tools.
This approach made it possible to test three things: whether the average body shape changes, whether the range of shapes narrows, and whether different lines of evolution are moving in the same direction.
What they found
The result was unexpected. Grasping legs did indeed appear in insects time and again. Moreover, different lineages often moved in a similar direction: the forelegs and the front part of the body changed particularly noticeably.
However, the scientists found no clear ‘convergence’ towards a single final form. In other words, evolution did not select a single winning design.
To put it simply: insects needed to catch their prey, but a variety of body designs proved sufficient for this purpose. Some lineages favoured certain proportions, whilst others favoured different ones. The function was similar, but the design was not identical.
Why this is interesting
We usually think like this: if there is one task, then there must be one best solution. If you need to swim fast, the body becomes streamlined. If you need to fly, wings appear. If you need to catch prey, the legs should become roughly the same.
But research reveals a more interesting picture. Evolution does not always work like an engineer searching for a single optimal design. Sometimes it achieves a similar function through different forms.
This means that in nature there may not be just one ‘ideal’ predator, but many viable options. For catching prey, the key factor is not how much a paw resembles a mantis’s claw, but how well it performs the task: to grab and hold quickly.
The head has changed too
The study revealed another important point. Along with their grasping legs, the heads and ‘necks’ of such insects often changed: the head became wider, and the section between the head and the body became longer.
This may be linked to vision. A wider head in a predatory insect may help it to better judge the distance to its prey. For a hunter that needs to strike accurately and quickly, this is crucial.
In other words, evolution has altered not only the ‘weapon’ but also the targeting system. The legs help to grasp the prey, whilst vision helps to calculate the right moment to strike.
Why this is important
The study shows that a similar function does not always mean the same form. This is an important clarification for evolutionary biology.
If one looks only at outward appearance, one might say: ‘Look, different insects have come to resemble mantises’. But if you measure body proportions and map out the different forms, the picture becomes more complex. They have evolved similar hunting strategies, but have not become copies of one another.
This helps us better understand how evolution creates new organs and new ways of life. Sometimes it really does lead different species to almost identical solutions. And sometimes it produces several different designs that work quite well.
Background
Mantis are the most recognisable example of insects with grasping forelegs. But they are not the only ones. Similar grasping limbs are found in various groups of insects, which did not inherit them from a common ‘predatory’ ancestor, but developed them independently.
This is precisely why such appendages are of interest to scientists. They allow us to test a key question: when different species face the same challenge, how predictable is the course of evolution?
A new study answers this: there is predictability, but it is limited. The direction may be similar, but the final outcome can vary.
Source
Study: H. Miyaji, T. Shinohara, A. Hirayama, Y. Takami, “Quantifying the repeated evolution of insect raptorial forelegs”, Scientific Reports, 2026.