We have answered the first question posed to us at Ask a Scientist!
Do caterpillars taste? Do they have tongues? Can you taste things without a tongue?
These are great questions, and it’s not just me that thinks so. Perhaps to your surprise (unless you study bugs for a living), the way caterpillars taste their food is a hot topic in the world of entomology. Lots of very smart people have made careers out of asking these same questions (including this guy, who is an expert on the topic, in case you are curious).
Many scientists try to answer these questions by studying the tobacco hornworm (Manduca sexta). M. sexta is a moth that, during its larval stage, grows into a 7-centimeter long bright green caterpillar. Why do scientists care so much about how this little creature eats? Well, as it turns out, we are not so worried about the caterpillar itself. Rather, scientists use M. sexta as a model organism for taste sensation and perception. This means that they study the sense of taste in M. sexta to understand how the sense of taste works in humans. Conveniently, M. sexta caterpillars have a complex gustatory (taste) system that is not unlike our own, and they are big enough that they are relatively easy to study.
Before I explain the ins and outs of the caterpillar gustatory system, however, it might help to get a little refresher on the workings of the human taste system.
Humans sense five different tastes: sweet, sour, bitter, salty, and umami (savory). Each of these tastes is detected using different receptors your tongue, but overall, they all follow a similar pathway to your brain. It all starts in your mouth – your mouth contains taste buds (the tongue is home to most of them), and inside these taste buds are taste cells. When a tastant (like salt or sugar) comes in contact with a taste cell, the cell sends a message through your tongue and a couple nerves to your brain, which tells it that that particular taste is there (find out more about the physiology of taste here). The brain then responds by making you feel a certain emotion and by telling you whether or not to continue eating.
Each taste serves a distinct purpose and affects the brain’s response differently. For instance, sweet taste signals nutrition, and in response, your brain makes you feel good and tells your jaws to keep chewing. In contrast, a bitter taste signals toxins and stops you from eating. Umami makes food palatable, salty taste helps you control your electrolyte (salt) balance, and sour taste, which is signaled by acids, helps you determine whether food is at its peak freshness or not (think milk). All of the flavors you have ever tasted are composed of one or more these five tastes, and these tastes all direct us towards eating foods that keep us healthy. As you can see, taste is a very important sense – without it, we would not be able to tell whether a food is nutritious, or even whether it is safe to eat (without consulting a biochemist).
For your third question (I’ll get to your first and second ones later), “can you taste things without a tongue?” we can answer this by looking at where your taste buds are located. Taste buds are mostly found on the tongue, but they are also found on the roof of your mouth, your throat, and even in your stomach (find out more about this here). Because your taste buds are all over the place, you might be able to taste things without a tongue. However, there are more taste buds on your tongue than anywhere else, so if you didn’t have a tongue, your food would not taste nearly as good. Tobacco hornworms, on the other hand, can definitely taste things without a tongue. How do we know that? Because they don’t have tongues!
Not only do tobacco hornworms not have tongues, but their mouths are also very different than ours. In fact, insects’ mouths, in general, do not look anything like human mouths. Instead of having a tongue, teeth, and gums, insects have “mouthparts” (scientists aren’t the most creative individuals when it comes to naming things). Mouthparts are shaped differently in different insects. For example, some mouthparts resemble straws, and bugs use them to suck up their food. Others resemble a mandible, or jawbone, which allows insects to chew up leaves (more about that here). Caterpillars carry these jawbone-like mouthparts. Since caterpillars do not have tongues, their taste buds are located on this “jawbone” instead (Glendinning and Hills 1997). Other insects have taste buds elsewhere, including some places you wouldn’t expect. For instance, moths and butterflies have taste buds on their feet so that they can sense whether or not to eat a plant just by landing on it!
Caterpillars can taste sweet, salty, and bitter, and umami tastes (Glendinning et al. 2007; Pszczolkowski et al. 2009), but mainly, the caterpillar is most sensitive to sweet and bitter tastes. These tastes serve the same function in caterpillars as they do in humans, dogs, chickens, bears, and most other animals. Generally, when a caterpillar encounters a sweet taste, its brain tells it to continue eating. When it encounters a bitter taste, its brain tells it to stop eating and move on, because, as you read above, bitter things tend to be toxic (Schoonhoven and Blom, 1988; Glendinning et al. 2002).
In summary, caterpillars can taste their food, but they don’t have tongues, proving that it is possible for some animals to taste their food without tongues. The next time you see a caterpillar, remind yourself that they care about how their food tastes, just like you. Also, remember that without them, we would not know nearly as much about how our own sense of taste works. Hooray for the little guys!
Neurobiologist and Co-Editor of the ISC blog
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