Considering San Diego’s status in the craft beer industry, people should not have a problem locating an establishment that will pour a celebratory frothy beverage on August 3, International Beer Day. In the grand tradition, crowds will convene at their favorite local tasting room, raise a pint, and enthusiastically declare the traditional International Beer Day toast, “Thank the gods for herbivorous insects!” Or at least that is how it should be.

Insects make the world taste great, beer included. Name your favorite hoppy flavor. Piney? Dank? Tropical? Peppery? The chemicals behind those flavor profiles are primarily three essential oils. You heard right, essential oils—beer drinking is aromatherapy!

But what does this have to do with insects? Plant-based essential oils generally fall in a class of chemicals called terpenes. They make lavender smell lavendery, mint plants smell minty, and hops smell hoppy. Plants don’t really need these essentials oils. More accurately, plants can do all the essentials like photosynthesis (making energy) and cellular respiration (consuming energy) without essential oils in the picture. So why do plants contain essential oils? In a nutshell, insects.

Essential oils generally serve two purposes in plants: 1) to make them taste bad to herbivores, or 2) to make them smell good to pollinators. Over evolutionary time, herbivorous insects have been in an evolutionary arms race with plants. Plants evolve gross tasting or poisonous chemicals to deter insect feeding. Insects evolve ways to neutralize those chemicals. And it escalates and escalates in some sort of Very Hungry Caterpillar – Cold War feedback loop. You can imagine an impassioned caterpillar proclaiming, “Mr. Gardenia, tear down this wall!”

Hops have essential oils in spades. Myrcene is peppery, caryophyllene is woody, and humulene is, well, hoppy. The particular blend of these and other essential oils are what create varying flavor profiles across different varieties of hops. Combine that with a bitter chemical called humulone, some barley and malt, and you get what some might call, “heavenly liquid aromatherapy.” Thank the gods for herbivorous insects.

Posted by Vice President of Science and Conservation and Curator of Entomology Michael Wall, Ph.D. .