Do Bugs Feel Pain?

Do Bugs Feel Pain?

by Brian Tomasik

First written: April 2009; last edited: 8 June 2014


Do bugs suffer? Does a fly caught in a spider's web consciously experience fear and pain? This piece aims to shed some light on that question by presenting quotations and references from a variety of sources. My personal conclusion is that we should give some weight to the possibility of bug suffering, especially until more evidence is available. Thus, considering the 1018 insects that exist at any given time, there is a huge amount of (potential) suffering in nature due to insects alone. We may also want to consider the ways in which humans impact insects, such as through insecticide use, although insecticides could potentially prevent more suffering than they cause if they avert vast numbers of future offspring that would have mostly died, possibly painfully, soon after being born. (Whether insecticides reduce or increase insect suffering on balance seems unclear. And of course, reducing insect habitat permanently would be more humane than simply spraying pesticides.)

See also: "How to Avoid Hurting Insects". One of the easiest tips is to avoid buying silk, since its production boils silk worms alive.

Table of contents

Suggestions of pain

Nociception vs. pain

Learning, memory, and motivation



Non-programmed behavior

Cognitive generalization

From Exploring Consciousness through the Study of Bees by Christof Koch:

Insects, in particular, were long thought to be simple, reflexive creatures with hardwired instinctual behaviors. No more. Consider the amazing capabilities of the honeybee, Apis mellifera. [...]

In humans, the short-term storage of symbolic information -- as when you enter an acquaintance's phone number into your iPhone's memory -- is associated with conscious processing. Can bees remember task-relevant information? The gold standard for evaluating working memory is the delayed matching-to-sample (DMTS) paradigm. The subject looks at a picture for a few seconds. The test image then disappears for five or 10 seconds. Subsequently, two pictures are shown next to each other, and the animal has to choose, by pushing a lever or moving its eyes, which of the two images was the test picture. This test can be carried out correctly only if the animal remembers the image. A more complex version, the delayed nonmatching-to-sample (DNMTS) task, requires one additional processing step: choosing the opposite image from the one previously shown.

Although bees can't be expected to push levers, they can be trained to take either the left or the right exit inside a cylinder modified for the DMTS test. A color disk serves as a cue at the entrance of the maze, so that the bee sees it before entering. Once within the maze, the bee has to choose the arm displaying the color that matches (DMTS) or differs from (DNMTS) the color at the entrance. Bees perform both tasks well. They even generalize to a situation they have never previously encountered. That is, once they've been trained with colors, they "get it" and can now follow a trail of vertical stripes if a disk with vertical gratings is left at the entrance of the maze. These experiments tell us that bees have learned an abstract relation (sameness in DMTS, difference in DNMTS) irrespective of the physical nature of the stimuli. The generalization to novel stimuli can even occur from odors to colors. [...]

Although these experiments do not tell us that bees are conscious, they caution us that we have no principled reason at this point to reject this assertion.

Social behavior

What about tissue damage?

Benefit of the doubt?

From entomologist Jeffrey Lockwood, "Do bugs feel pain?":

So, given that we can't be sure whether insects experience pain, how should we treat these creatures? When I was teaching insect anatomy and physiology I insisted that the students anesthetized insects before conducting experiments that we would expect to inflict pain on a mouse. [...]

[One reason is] it seems ethically obligatory to guard against the possibility that insects feel pain. If we use anesthetic and it turns out that insects don't experience pain, the material cost of our mistake is very low (a few extra minutes to apply cold or carbon dioxide). However, if we don't use anesthetic and it turns out that the insects were in agony, then the moral cost of our mistake is quite high.

In general I agree with this sentiment. As a matter of detail, I would not use exactly this "precautionary principle" approach of giving insects the benefit of the doubt. I would instead multiply possible insect suffering by a probability of sentience; this makes the ethical tradeoffs between insects, which may or may not suffer, more fair against animals we know can suffer. However, given that insects have a probability of sentience that isn't too small, their potential suffering still tends to dominate calculations even when multiplied by 50%, or 10%, or even 1%. My own probability for sentience is ~40%.[1] Considering how easy it is to avoid causing harm to so many insects, on a macro scale and even in our daily lives, any reasonable sentience probability will imply significant consequences for our actions.

Further reading


[1] I now don't believe that whether insects are sentient is an objective factual question, so talking about probabilities isn't quite accurate. Fundamentally, whether we care about insects is a moral choice. However, facts are very relevant in informing us about (a) what abilities insects actually have and (b) what types of abilities in humans correspond to conscious emotion. For instance, we might have thought that a given cognitive trait was important for human emotional experience but later learn that it's completely irrelevant, and in that case, the fact that insects have it would not be as pertinent as we had presumed. And the same could be true in the opposite direction. So one way to continue using probabilities is to ask "How likely would I be to care about insects if I learned and thought more about the topic for a long time?"

Beyond this, I think sentience should be seen to come in gradations, in which case the question is less whether insects matter or not in a binary fashion but how much they matter. I think it's very likely I would care to some degree about insects upon further reflection, but whether I would care a little or a lot remains uncertain. At the moment I would guess that I value preventing one dog from suffering at around the same as preventing ~100 insect from suffering in an analogous way. This assessment is likely to change over time.

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