Interviewee: Dr. Joni Ollonen, biologist.
Specialised in skull development in squamates.

Interviewers: Curator Tiina Rauhala and Artist Maija Tammi, Doctor of Arts

T: Lilli, the migratory locust in Hulda & Lilli, doesn’t swarm due to an intestinal parasite. Why do locusts, these otherwise solitary creatures, start swarming in their millions from time to time?

JO: Most of the time, migratory locusts are like your everyday grasshoppers: solitary. But when their population density grows high enough, for instance when locusts congregate in such numbers that they literally start colliding with each other, their hormonal activity changes. This in turn causes changes to their nervous system and behaviour, but their colouration and the functioning of their flight muscles are also affected.

Behind these changes lies phenotypic plasticity – a phenomenon by which the same set of genes can translate into a multitude of different-looking things depending on the timing and location of gene expression, how the genes are read. For example, swarming locusts aren’t as fast flyers as solitary ones, but thanks to their increased endurance, they are able to fly much further. How often swarming occurs is most likely cyclical, but it is known to have been happening throughout all of history. Swarming already shows up in records dating back to Ancient Egypt.

M: Fittingly, migratory locusts have been called the Dr Jekyll and Mr Hyde of the insect world, after the 1886 novella by Robert Louis Stevenson.

T&M: How old is the migratory locust as a species?
JO: In a general sense, grasshoppers have existed for some 60 million years. More broadly speaking, grasshopper-like species date back to the Permian period, between 250–300 million years ago, when vertebrates were mainly creatures that a layperson would call fish.

T&M: What is the migratory locust’s life cycle like? 
JO: The locust does not have a larval stage and instead hatches out already looking more or less like an adult locust, only smaller. When it grows, it moults away its exoskeleton approximately five times, each time growing a new shell beneath the old one. This new exoskeleton stays elastic for a while, allowing for the locust’s growth. Initially, it’s unable to fly – at least very effectively – because its wings become fully functional only after the last moult.

Locusts utilise a numerous-offspring-at-once tactic, and depending on the exact species, a female might be able to produce a couple clutches, usually a few weeks apart. A locust’s life or complete life cycle lasts for about 2.5 to 5 months depending on ambient temperature and sunlight levels. In theory, they could live longer, but they’d be very lucky to do so, as they serve as sustenance to quite many other animals. In addition, the females get worn out by egg-laying, so to speak.

T&M: What role do locusts play in ecosystems? 
JO: As solitary animals, they likely serve the same role as each and any herbivorous insect – a component in nutrient cycling: locusts eat plants and get eaten by other animals. They speed up nitrogen cycling in ecosystems.

On the other hand, in the gregarious swarming form, they can eat up whole crop fields and thus affect food production for the masses. Otherwise, they do also affect nutrient cycling in the same manner as solitary animals, just at a different magnitude.

T&M: How widespread are locusts? 
JO: The migratory locust is the most widespread locust species in the world. It visits Northern Europe only now and then and is unable to reproduce here.

To my understanding, locusts are currently so abundant that different types of pesticides and biological methods are used to try to keep their swarming in check. An example of this is the intestinal parasite mentioned previously.

T&M: How do locusts jump and fly?
JO: As it happens, it isn’t really so much about muscle but rather about utilising their exoskeletons, which they figuratively draw like bows for shooting and then keep taut with latches; when the latch is released, the grasshopper shoots off. For small insects, this is a way of powering movement much more effective than pure muscle.

To be specific, grasshoppers don’t move their wings directly but rather by pumping their thoraxes - their bodies’ middle sections – as do so many other groups of insects. This is effective in and of itself, as the insects simultaneously get oxygen pumping through their bodies via tracheae, or “air pipes”.

T&M: What is the locust’s behaviour like?
JO: Locusts are exothermic, or “cold-blooded,” so ambient temperature affects their activity. They’re mostly active in the daytime, but as they lie at the bottom end of food chains, they’re not likely to afford lazing about even at night – rather, they’ll be proactively procreating, as is the intention behind their chirping.

T&M: The veiled chameleon (Chamaeleo calyptratus) has paws that look like mittens. Why is that?
JO: Even us humans possess similar webbed mitts – flippers, if you will – during our embryonic development, but these are then sculpted into our fingers and toes as certain cells forming the webs between them die off. Two to three toes on the chameleon’s feet stay together, meaning these toes don’t get cells dying off from between them. Thanks in part to this, the chameleon’s grip becomes stronger.

T&M: What is the veiled chameleon like as a species?
JO: A very old one, at least when compared to us humans. Chameleons were already around some 100 million years ago, the end of the Cretaceous period, so they coexisted with dinosaurs. From those times, they’ve certainly diversified as a group.

Chameleons belong to acrodonts, or “long-toothed lizards,” who commonly have cartoonishly large eyes – a telltale sign of exactly how much they rely on their vision. In the past, chameleons have been called “ground-lions”; this was likely due to the bony ridges on their heads, reminiscent to some of a lion’s mane.

M: From what I’ve read, chameleons are often feared and regarded as bad omens – evil spirits, even – in Madagascar and sub-Saharan Africa.

T&M: What role does the ridge on a chameleon’s head play? 
JO: There’s some uncertainty about this, but it could play a role in intraspecific communication, in how animals of the same species communicate with each other. And as bones function as surfaces for muscle attachment, the ridge might also enhance biting force. Or then again, the ridge could just be a useless piece of courtship bits and bobs, brought about by sexual selection – not unlike a peacock’s tail, functionally useless to the bird and only advertising such an abundance of resources that the male can actually sustain such swank. Or the ridge could be a bit of everything mentioned above.

T&M: Why do chameleons see ultraviolet light (UV)?
JO: Actually, some chameleon species also have bones that glow under UV light, so they’re these party animals geared up for a night out on the town. Most likely this is about communication, and chameleons have these UV-enabled receptors in their eyes.

Besides, they’re anyway able to use their eyes to look in two different directions simultaneously and still form a cohesive picture. Peeking into a chameleon’s brain, one notices the sheer bulk of the parts that have to do with vision, and the optic nerve is just plain huge.

T&M: Why and when do chameleons lay eggs? 
JO: If and how often they lay eggs depends on food availability, and they can also lay eggs without mating. These types of eggs naturally don’t develop into new individuals.

With lots of food available, a female can lay up to four clutches a year, but this is likely to leave its lifespan on the short side. An overabundance of food in captivity might also make a female produce too many eggs, rendering it unable to lay them. Alternatively, the female may jostle the eggs out but then die of exhaustion. Egg-laying is a huge investment, requiring loads of energy and especially calcium.

T: So a bit like a burdensome period?
JO: Unfertilised eggs could be described as such, yes – the same as chicken eggs at a grocery.

T&M: How and why do chameleons change their colour?
JO: That’s a splendid mechanism. This ability is based on iridescence, or on how light gets reflected – a mechanism different from, say, how colouration works in us humans. Iridescence is about reflective structures, whereas we have pigments that absorb light in different ways. Chameleons’ reflective cells have these crystal-like discs that change their formation and width according to how the cell is distended or compressed; these crystalline discs then reflect light in various ways. And as chameleons are able to affect the cell length just by adjusting ion (salt) concentrations around these cells, they can change their colouration very swiftly.

The changes in colouration appear to serve three main functions. Firstly, they exist for intraspecific communication; secondly, for thermal regulation; and lastly, for some camouflage – maybe. Out of these three, intraspecific communication is likely the factor most responsible for driving evolutionary change, as at least one study shows that the animals’ colouration is highly visible to both other chameleons and the birds that prey on them (although it can help reduce the total amount of other animals capable of eating them). As an example, female chameleons who notice a male but don’t wish to mate turn completely dark, save for specks of yellow and neon blue. Chameleons detest each other outside mating season and are loners in general, too. One might venture to call them very Finnish lizards.

In addition, just by changing their colouration, these animals can adjust exactly how much their bodies get warmed up by ambient sunlight. This is significant, as they’re ectothermic creatures. So even though cartoons tell a different tale, camouflage isn’t the main reason behind changes in colouration. We now know that it’s instead more a way for the lizards to put themselves on display and express their feelings, even though all this is invisible to human light receptors.

Not only can chameleons change colour but body shape, too. When irate, they often balloon up; other times, they might hide behind a twig or branch by slimming down like flatbread; or they might imitate leaves or grass swaying in the wind, all whilst sauntering on the ground.

T&M: How long can a chameleon live for? 
JO: Having raised them for some ten years, Mari and Peetri Joki are better suited for answering this question. 

Mari & Peetri Joki: Apparently, only a small percentage of veiled chameleons survive their first winter in the wild. In captivity, as pets and under optimal conditions, males could exceed and females nearly reach the ten-year mark; in practice, the females live for two to three years and the males for about five.

T&M: Hulda & Lilli plays with the nature-documentary thematic. What goes through a biologist’s mind when watching a classic nature documentary?
JO: Well-made nature pictures are impressive to look at, technique-wise, such as the scene in Planet Earth with a lizard running from snakes. 

But narration-wise, nature documentaries tend to say a lot with scarcely any actual meaning. An example of this could be, “Beavers play a role in ecosystems.” This is akin to answering an exam hung-over and without having read up. The documentaries often recycle clichés, and these slightly forced narrative arcs, even though the reality of our everyday natural world doesn’t provide for such thrilling dramatics.

In general, I have this feeling of viewers being underestimated in their capacity for taking in complex information or becoming interested in new things. And perhaps nature documentaries could escort us outside our comfort zones regarding how extravagant or dramatic things truly are. After all, all things natural are in and of themselves interesting, unless you happen to be utterly dull. 

Translated from Finnish into English by Mikko Aulio.