As a child I remember looking at the sticky yellow tapes handing in people’s houses. Fly traps. Countless flies died on that yellow piece of tape, trying to escape in vain. Back in the 1990s, an upgraded version of a fly trap displayed in countless stores was an electric fly trap, with neon purple long, cylindrical bulbs, surrounded by a metal cage. The buzzing of the trap was unnerving, and every few minutes I could hear a quick “zap” and a fly would fall to its demise. Underneath the apparatus, a fly cemetery was building up. At a time, nobody talked about insect pain, it was a foreign concept.
Around 2007, I began to work at a fly laboratory as an undergraduate student. Specifically, I worked with small fruit flies, Drosophila melanogaster, often found flying around ripe fruits left on the countertops. The more I learn about them, the more fascinated they become. They were living creatures, kept in plastic bottles filled with a mixture of agar, cornmeal, yeast, various sugars, and antifungals like Tegosept. The smell of the fly food would penetrate the entire floor of the Science building, and we often had to make it from scratch, pour it into tiny bottles, caps, and packages for storage into the refrigerator. As an undergraduate, capping fly food was one of those things we dreaded the most.
During that time I learned about the nervous system of a fly. Fruit flies, like most other insects, have a nervous system made out of the brain and thoracic ganglion, or a fly equivalent to the human spinal cord (note that flies are invertebrates and do not have a spinal cord). To my surprise, flies have a whole array of behaviors such as flying, color vision, great sense of smell and taste, sense of balance, courtship, they have a sense of day and night, and many others. The most important however is their ability to sense noxious stimuli. Many insect ideas and anecdotes are more fully discussed in the book by Jonathan Balcombe The Super Fly: The Unexpected Lives of the World’s Most Successful Insects.
A fly learns about its surroundings very quickly. Flies learn to avoid experimental chambers associated with pain from electric shock, unpleasant smell, high or low temperatures, and other stimuli affecting their various senses. A more recent study showed that flies can even experience chronic pain.
The idea that insect experience pain is not universally accepted. The question is why not? I think most of this comes from the notion that if an animal cannot express pain in a way we can recognize, we think that it does not feel pain. This is strange, as insects have the relevant pain receptors, for example nociceptors that respond to increased heat. A mutant fly, painless, fails to respond to increased heat, when its nociceptive receptors are missing from its sensory neurons. We know of human cases with inability to sense pain, a very dangerous condition, because our ability to sense pain is one of our survival skills. Sensing pain tells us that is wrong with our bodies and that we should take notice. Flies do the same as they also need to be able to tell when something is wrong.
Another part of the issue is that flies can have negative consequences to our health. Certain species of flies, such as Tzetze common to Sub-Saharan Africa can carry parasites leading to sleeping sickness, which can be fatal. Common house fly, Musca domestica, are known to carry multiple pathogens, many of which are dangerous to humans and animals. This does not help their reputation.
This love and hate relationship with flies is a part of life. Flies are critical to the environment, as they are a major food source to many species of fish, spiders, birds, dragonflies, beetles, ants, to name a few. Thus, we have to recognize and acknowledge their abilities too.
We are not the only species with a nervous system, and maybe we have to open our eyes a little bit to see beyond ourselves.