The case for insect sentience (1/2): The evidence
A review of current research insights with expert Prof. Bob Fischer
Author: Elisa Autric,1 in collaboration with Bob Fischer.
On October 20, 2025, Rethink Priorities (RP) hosted “What do we know about insect sentience?,” a webinar examining the current state of knowledge about insect sentience and exploring critical questions concerning how to best protect insect welfare. The session featured Prof. Bob Fischer, a Senior Researcher at Rethink Priorities, Professor at Texas University, and Director of Arthropoda Foundation.
This post is the first of a two-part series related to this webinar. It contextualizes and summarizes the contents of Bob Fischer’s presentation on the evidence for insect sentience. An upcoming post will summarize the answers he gave during the Q&A session of the webinar, particularly on the implications of this data for insect-welfare-minded advocates and funders.
The potential scale of insect suffering
Insects represent an extraordinary portion of animal life on Earth, with 200 million insects for every human, over 1 million known species, and an estimated 5.5 million species total.
The rise of insect farming
We’ve also uncovered a concerning trend: the explosive growth of insect farming since the late 2010s.
Originally promoted as a circular-economy solution for converting food waste into protein, fertilizer, and bioplastics, insect farming is increasingly industrialized, spanning from high-tech facilities in Europe and the US to small-scale operations in Africa and Southeast Asia.
According to our forecasts, the number of farmed insects could reach trillions by 2033; yet, very little consideration has been given to their welfare.
Current on-farm welfare concerns
Several welfare issues pervade insect farming across production scales. For example, farmed black soldier flies (the species that has seen the most recent production growth) face:
Inhumane slaughter: Unlike mammalian agriculture, where animals are rendered insensate before death, insects are typically killed through microwaving, baking, or boiling. These processes can take 30 seconds to several minutes. In lower-tech environments where larvae are spread on plastic mats to desiccate, death can take much longer.
Adult starvation: The industry long operated under the mistaken assumption that adult black soldier flies don’t eat. While they do have functioning mouthparts and will consume nutrient-laden liquids, adults are traditionally not fed and starve to death after several days.
Other concerns include larval overheating from aggregation, suboptimal environmental conditions, and lack of feed enrichment.
The evidence regarding insect sentience
The groundwork: What is sentience?
Let’s clarify some key concepts: Consciousness refers to whether “the lights are on.” i.e., whether there’s something it’s like to be a particular individual. Sentience is a specific form of consciousness that involves both positive and negative affect.
Critically, sentience doesn’t require complex cognition, nor does complex cognition suffice as a criterion for sentience. While honeybees, for example, now show evidence of understanding the concept of zero—an impressive cognitive feat—this isn’t relevant to sentience. Sentience is about subjective feeling, not cognitive sophistication.
Assessing sentience in insects
One way of assessing sentience involves a three-pronged approach, considering behavioral similarities, neurophysiological mechanisms, and evolutionary dynamics.
The framework developed by Jonathan Birch and colleagues in their 2021 LSE report on cephalopod and decapod sentience evaluates eight behavioral and neurophysiological criteria for sentience, including:
Possession of nociceptors
Possession of integrative brain regions
Connections between nociceptors and integrative brain regions
Responses affected by potential local anaesthetics or analgesics
Motivational trade-offs
Flexible self-protective behaviors
Associative learning
Valuing of analgesics or anaesthetics when injured
The evidence to date
A comprehensive 2022 review titled “Can insects feel pain?” by Matilda Gibbons and colleagues applied Jonathan Birch’s precautionary framework to six insect orders. They found:
That adult Diptera (the order of flies, including the commonly farmed black soldier fly and mosquitoes), and Blattodea (cockroaches and termites) “satisfy six criteria, constituting strong [precautionary] evidence for pain.”
Juveniles of these orders, as well as those of one more order and adults of three other orders, all qualified for “substantial evidence for pain” under the Birch framework (3-4 criteria met).
Notably, the evidence base has strengthened since 2022, with additional research addressing previously understudied criteria. The evidence quality for sentience in some insects now matches or exceeds that for lobsters and crabs, animals many people readily grant moral consideration.
The scientific community’s use of insects as pain research models provides additional evidence.
Fruit flies are regularly used to study human pain mechanisms.
In one striking 2023 study, researchers inserted human capsaicin receptors into fruit fly larvae—and the receptors worked seamlessly, producing the expected pain behaviors (see video). The researchers celebrated this as proof that the underlying mechanisms of pain are highly conserved, inadvertently strengthening the case for insect sentience.
Along with experimental and theoretical assessment of behavioral and neurophysiological criteria of sentience, we should take into account the following evolutionary considerations:
Taxonomic relationships: Insects belong to the same taxonomic group as crabs and lobsters. If we grant crustaceans the benefit of the doubt on sentience, consistency suggests we should do the same for insects.
The origins of sentience: If invertebrates (like octopuses) and mammals (like humans) both possess sentience despite their last common ancestor being a simple bilateral worm 700 million years ago, this suggests either (1) sentience is ancient and widely distributed, or (2) it emerged independently at least twice. If the latter, we must ask what evolutionary pressures made sentience valuable enough to evolve multiple times, and why those same pressures wouldn’t apply to invertebrate taxa other than octopuses, like insects.
Confronting our biases
Cognitive biases significantly influence our intuitions about insect sentience. Black soldier fly larvae, for example, look quite different from the charismatic animals we readily consider sentient, like bunnies or giraffes.
Consider this thought experiment: if insects were large, rare, non-threatening savannah creatures with identical brain architecture and abilities, most people would likely find insect sentience obvious.
This suggests we should be “cautious of our own wariness”: not necessarily becoming highly confident in insect sentience, but checking our tendency to dismiss the possibility based on factors that don’t track the scientific evidence.
Learn more about insect sentience and farming
To learn more about insect sentience and welfare, you can dive into our:
Foundational pieces on insect farming:
Explorations of current on-farm welfare concerns for the species most commonly farmed as food and feed:
Reviews of farmed silkworm, managed honey bee, and wild moth welfare.
And, of course, stay tuned for the second part of this Substack series, focusing on the implications of this evidence for insect welfare-minded advocates and funders.
Acknowledgements
Many thanks to Bob Fischer for sharing his expertise in the webinar and for his feedback on this post. Thank you to Urszula Zarosa for organizing the webinar and for feedback, and to Shane Coburn for copyediting.
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Disclosure: This piece was drafted by Elisa Autric with support from an AI assistant (in line with RP’s AI use policy). Our team reviewed it for accuracy, clarity, and tone. We use this approach to produce high-quality work while optimizing our resources.
Important post!