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How very hungry caterpillars grow and grow and don't get sick

What if I told you that right in your backyard there lives a creature that eats five times its weight every day and grows a thousandfold in weeks. Instinctively, you'd probably want to stay away from the gluttonous beast! However, it wouldn't be interested in you at all—in fact, it's a vegan. Feel safer now?

Well, you shouldn't.

You may have come across this gluttonous beast in kindergarten: the hungry hungry caterpillar, who ate his way through pages of food. Humanity loses to crop pests like caterpillars every year. To put this in perspective, this is .

Caterpillar growth

Caterpillars turn into butterflies and moths, which are important pollinators of plants and crops. So, this group of insects is like a very nice couple with a few very annoying kids.

Caterpillars have to grow a thousandfold in weeks, while eating nothing but leaves. In order to digest plants better, caterpillars produce a , similar in properties to commercial cleaning products.

In addition, plants that are fed on by insects , which caterpillars must be able to render harmless. Rapid growth usually requires the best food and easiest metabolism. So, how does a creature that feeds on toxic plants and produces detergent in its gut grow so rapidly?

There is no delicate way of putting it: caterpillars are able to do this by pooping (not addressed in this article) and peeing effectively. Until now, how insects pee has been studied in and , but not caterpillars. But you can't learn how a whale pees by studying a camel.

Caterpillar kidney design

For the past five years, members of Michael O'Donnell's lab at McMaster University (including myself) have been investigating . It turns out that caterpillar kidneys—outpouchings of the gut termed Malpighian tubules—have several cool adaptations that enable caterpillars to safely consume so much food.

when compared to those of other insects—they are closer in complexity to human kidneys than those of adult moths and butterflies of the same species. Generally, animal kidneys require water flow from blood into the kidney because toxic wastes need to be dissolved in water so they can be excreted.

Caterpillar , enabling them to extract water from their food instead of using water from their blood. In fact, not only do caterpillars power their excretion with gut water, they use their kidneys to transfer some of the gut water into their blood, which helps them to grow rapidly.

However, this arrangement doesn't work when there's not enough water in the gut. In this case, the caterpillar kidney , so it can work uninterrupted. This allows their kidney to use water from the caterpillar's blood to produce urine.

This switch is very rapid and involves . This allows the caterpillar to work their kidneys non-stop regardless of whether it's feeding or not.

Caterpillars' kidneys can , minimizing how much water they lose to peeing.

Caterpillar research

It took us several years to begin understanding and .

Our work at McMaster University shows us how caterpillars have highly efficient kidneys that enable their growth. Understanding this can help us interfere with their feeding on our crops. Of particular importance is how the caterpillar kidney is different from that of other animals (including us). This will ensure that any control strategies implemented will not affect the bees, birds and humans in the same habitat.

Now, more than ever, while faced with COVID-related food shortages, we must be cognizant of where our food comes from and what it takes for it to get to us. Finding out how caterpillars pee will help us put a dent in that $470 billion of crops we lose to insect pests every year.