This piece was authored by a volunteer contributor, Nicholas Souter.
The importance of welfare considerations for farmed animals can be affected by several factors. Cognition refers to mental processes including memory, learning, and problem solving, whereas sentience is the ability to have subjective feelings and experiences.1 Despite the growth of insect farming, there has been little research into farmed insect cognition. Conclusions regarding farmed insect sentience remain even less clear. Nevertheless, some have advocated for a “precautionary principle,” that unless farmed insects can be concluded not to be sentient, their welfare should be considered.2 This is based on the idea that “when faced with such little research, we cannot assume that absence of evidence, is evidence of absence.”3 Increased understanding of farmed insect sentience may rely on further research, which is theoretically and methodologically appropriate to address this question.
At present, there is insufficient evidence to conclude the presence of sentience in farmed insects. However, the scale of insect farming is considerable. We believe that conducting further research into the sentience of commonly farmed insects could be an effective strategy for highlighting potential animal welfare concerns in a rapidly developing industry. In the face of insufficient evidence, we adhere to the precautionary principle on this topic, assuming sentience in farmed insects until evidence confirms otherwise.
Farming insects for nonhuman animal feed and human consumption has been increasingly studied as a cost-effective and environmentally friendly alternative to traditional animal protein sources,4 such as chickens, pigs, and fishes. Despite the relative novelty of insect farming, an estimated 1–1.2 trillion insects (largely comprised of crickets, mealworms, and black soldier flies) are slaughtered, sold live, or pre-processed annually.5 Insects account for the majority of farmed invertebrates. Other commonly farmed invertebrates include decapod crustaceans (e.g., crabs, lobsters, and shrimp), with an estimated 253–605 billion farmed a year as of 2017.6 The farming of octopuses (a cephalopod mollusk) is less common—the world’s first commercial octopus farm is set to open in 2023.7
The scale of invertebrate farming motivates the consideration of these species’ sentience and capacity to suffer. Sentience can be defined as the capacity for both positive and negative subjective feelings and experiences.8 Of relevance to farmed invertebrate welfare are subjective experiences of pain, suffering, and stress. A recent report9 that reviewed the evidence of sentience in cephalopod mollusks and decapod crustaceans resulted in such species being officially recognized as sentient in U.K. government policy under the Animal Welfare (Sentience) Bill.10 This review will focus on evidence for sentience in farmed insects due to the fact they have not received this degree of attention and the vast numbers in which they are farmed.
Determining Sentience in Farmed Insects
There is considerable disagreement concerning the likelihood of sentience in insects and the appropriate methods for determining so. Some have adopted an “argument by analogy” approach, supposing that the potential for suffering can be determined by looking for behaviors in insects that would suggest conscious pain in humans.11 Others question this approach. For example, the case for conscious pain in insects may be challenged by the simplicity of their central nervous systems, including their brains, relative to mammals.12 However, such anatomical differences do not necessarily mean that insects do not experience suffering comparable to mammals—cephalopods and crustaceans have an advanced visual system that evolved independently from visual ability in humans.13 Selective pressures may similarly have resulted in the capacity for suffering in insects, serving the same function as it does in vertebrates.
The case for conscious pain in insects may be supported by anatomical and functional similarities to mammals. The capacity for conscious pain is strongly associated with nociceptors: receptors specialized for detecting damage that send signals to the central nervous system and result in reflex withdrawal (a process known as nociception).14 Evidence for nociception similar to mammals has been reported in a wide range of insects, although it is argued that this system may be more specialized in mammals with evolution of the central nervous system.15 This is further complicated by the fact that nociception in humans does not always go hand in hand with the negative emotions we associate with conscious pain.16 Direct anatomical comparisons between species may therefore be limited in their current capacity to quantify suffering in farmed insects.
Reviews of farmed insect sentience acknowledge the lack of research on this topic, with many behavioral studies instead focusing on cognitive ability as a possible indicator of the capacity for subjective states, rather than assessing emotional experience directly.17 Several insects have received disproportionate research attention, including fruit flies18 and honeybees.19 Crickets are perhaps the most studied of farmed insects.
At 370–430 billion a year, crickets are the most widely farmed insects,20 and have been the focus of many behavioral studies. For instance, crickets have been shown to display context-dependent learning—selectively selecting or avoiding certain odors on the basis of light conditions.21 While such evidence could be used to suggest the existence of the more sophisticated operant conditioning, the authors argue that this is likely a product of simple classical conditioning.22, 23 Later research24 provided evidence of second-order classical conditioning in crickets, whereby a conditioned stimulus can indirectly be used to reinforce the properties of an unconditioned stimulus. This was observed for both appetitive and aversive stimuli. Evidence from this study also suggested common processes in the brain across insects and vertebrates.
Evidence for emotional experience is limited. Following exposure to a mock predator, crickets have been shown to present with behavioral signs of chronic stress including reduced weight gain, increased sustained flight, and increased concentration of a stress hormone.25 Such observations could suggest the existence of negative experiences in crickets, comparable to stress responses in vertebrates. Alternatively, this could reflect natural responses to the environment in the absence of conscious experience. The state of evidence of crickets is indicative of knowledge concerning other widely researched insects and provides perhaps the most insight into cognitive abilities of farmed invertebrates. Despite this, current methods appear insufficient to determine the likelihood of their sentience.
Despite being the second most frequently farmed insects at 290-310 billion a year,26 we were unable to find any research into cognitive abilities, sentience, or capacity for suffering in mealworms, the larvae of the mealworm beetle. Of nearest relevance was evidence for numerical cognition in mature mealworm beetles,27 though this is unlikely to provide insight into higher cognitive functions. Any existing welfare considerations for mealworms prioritize immediately observable biological function28 or nutritional value,29 rather than the capacity for positive or negative experience.
Black Soldier Flies
An estimated 190–300 billion black soldier flies are farmed annually.30 Despite this, very little has been reported concerning their capacity for cognition or sentience beyond evidence for feed preferences.31 While Parodi et al. (2020) argue for the need to therefore investigate black soldier flies’ capacity for distress and discomfort, such work has not been conducted to our knowledge. In terms of basic biological function alone, black soldier flies have been acknowledged as highly sensitive to external environmental factors, increasing the potential relevance of welfare considerations.32
As stated, sufficient evidence exists to allow conclusions regarding sentience in some invertebrates, including decapod crustaceans and cephalopod molluscs.33 Similarly, certain insect species have been extensively researched in terms of cognitive abilities, such as honeybees.34 It is unclear whether such findings are likely to generalize to farmed insect species, given that markers of sentience are not uniform across invertebrate taxa35. Research explicitly investigating the capacity for cognition and sentience in commonly farmed insects, such as crickets, black soldier flies, and mealworms, may prove effective in addressing this concern.
To view all of the works cited in this report, see the reference list.
Classical conditioning involves associating stimuli with involuntary responses, operant conditioning requires associating a voluntary behavior with a given consequence. More info here.