Humane Insecticides - Four Month Update

Hollis Howe

Previously, we proposed a research project investigating the feasibility of a humane insecticides program. Near-term interventions to improve the welfare of wild insects are a priority because invertebrate welfare, like wild animal welfare in general, is a neglected cause area, and the enormous number of insects together with the likelihood that their welfare is poor means that the potential impact of such interventions is high.

We identified humane insecticides as a promising near-term intervention to improve the welfare of wild insects. Employing insecticides which kill faster, less painfully, or both has the potential to greatly impact wild insect suffering without altering the number of insects killed or introducing new and potentially negative downstream ecological effects.

To date, we have reviewed existing literature on invertebrate sentience and capacity for pain, built a database of 255 insecticides and have begun documenting their modes of action, producers, and other relevant information. We’ve also begun conversations with outside academics on the viability of the project.

There are several factors that could limit progress on this project. First, little is known about insect welfare, and scientific opinion is split on the issue of invertebrate (including insect) sentience (for example, see Carere et al 2011 and Mason 2011, or Lockwood 1987 and Eisemann et al 1984). If there is even a small chance that insects can experience pain, the large number of individuals affected make this a morally pressing issue. However, if the scientific community and general public are unconvinced of insect sentience, it may be difficult to convince stakeholders that insects are worth moral consideration. We therefore conducted an in-depth review of relevant literature, to inform our work and to assess current views on the likelihood of insects experiencing pain.

The results of the literature review were mixed. Traditionally, sentience was considered to be solely a trait of vertebrate animals, or even a trait unique to humans. But, it is important to disentangle taxonomic bias from our investigations into nonhuman sentience. Despite being invertebrates, cephalopods such as octopus and cuttlefish are now generally accepted to be sentient, largely owing to an increased understanding of their behavior and cognition (Horvath et al 2013, Mather 2001). Even researchers who are unconvinced of invertebrate sentience recommend precaution when performing procedures that would be presumed to be painful in a vertebrate animal, such as anesthetizing before dissection (Wigglesworth 1980, Sneddon et al 2014, Smith 1991, Eisemann et al 1984). The American Veterinary Medical Association includes invertebrates in their Guidelines for the Euthanasia of Animals (AVMA 2013).

The relative simplicity of insect brains is sometimes taken as evidence against insect sentience. Interestingly, however, number of neurons, brain size, and structural similarity to vertebrate brains may not be definitive indicators of subjective experience. Insect brains are smaller and have fewer neural connections than those of vertebrates, but they may be more efficient, as insect brains are able to achieve analogous functions to vertebrate brains using fewer neurons (Klein and Barron 2016, Strausfeld and Hirth 2013, Chittka and Niven 2009, Lockwood 1987). Insect brains support behavioral repertories which allow insects to effectively carry out necessary tasks in shifting environments. The complexity and flexibility of some insects’ behaviors suggest that they are more than merely autonomic responses to simple inputs, and instead are produced through centralized processing of information (Klein and Barron 2016, Lockwood 1987). Insect behaviors are deemed similar enough to those of vertebrates that they are widely used in laboratory experiments to model cognitive processes in vertebrates (Perry et al 2013).

Specific behaviors common to the vertebrate experience of pain may not translate to invertebrates, even if they are experiencing pain. One hallmark of the vertebrate pain response is prioritizing a response to the painful stimulus over other behaviors, such as foraging (Sneddon et al 2014, Smith 1991). Some insects, such as mantises, are observed to continue normal behaviors after receiving stimuli that would be painful to vertebrates, such as a pin piercing the abdomen, the removal of a limb, or conspecific predation by mates (Eisemann et al 1984). This is often cited as evidence against the hypothesis that insects are sentient, but it is not enough evidence to reasonably reject the hypothesis altogether. A lack of measurable response to these stimuli does not necessarily mean that the insect is not experiencing pain, and it is also possible that while the tested stimuli are not painful to insects, others are. Some insects do show strong behavioral responses to (and learned avoidance of) some damaging stimuli, such as heat or electric shock, that take priority over foraging, mating, and other behaviors (Horvath et al 2013, Elwood 2011, Wigglesworth 1980).

It is possible for behavioral responses to potentially painful stimuli to be fully reflexive. One example in vertebrates is the reflex that causes you to withdraw your hand from a hot pan, even before the signal reaches your brain. It is even possible for simple learning to occur without central processing, as in the case of long-term nociceptive sensitization (Smith 1991, Eisemann et al 1984). That central processing of nociceptive information is not required for simple avoidance of noxious stimuli could be taken as evidence against insect sentience. However, the complexity of behaviors that insects deploy to avoid potentially painful stimuli make a merely autonomic response less likely. Additionally, some insects show intricate social, foraging, and other behaviors that suggest central processing of information and the possibility of motivational states, such as painfulness (Klein and Barron 2016).

The possibility that insects experience pain cannot be dismissed, and as our understanding of insect behavior and cognition improves we may be able to say that they probably do experience pain. The vast majority of the literature on insect sentience concludes that it is prudent to proceed as if insects used in research are capable of experiencing pain. Even if we assign a low likelihood of sentience to many insects, it may be that so many are impacted by insecticides that the expected value of implementing a humane insecticide program is extremely high. Determining the least painful methods of killing agricultural pest insects is a reasonable extension of this precautionary principle, especially as the number of insects impacted by agriculture probably vastly outnumber those used in research.

Another challenge faced in this project is the availability of information about how painful insecticides may be. Our review of literature on insecticides so far has been cursory, but most of the available information is regarding particular compounds’ modes of action, or the general mechanism by which they kill insects (Sparks and Nauen 2014). We have uncovered little information on how an insecticide seems to be experienced by affected insects. If we are unable to find sufficient information to rank the presumed painfulness of different insecticidal mechanisms, we can investigate which insecticides kill in the shortest time. We will continue to develop our database of insecticides currently used, their modes of action, their distributors, prevalence and usage patterns, and the duration of their potentially painful effects. These data will inform our advocacy approach.

Partnering with domain experts will be crucial to developing an informed and effective strategy for reducing wild insect suffering. We have developed a research memo outlining the goals of our project and the progress we have made so far, and identified academic contacts with domain expertise relevant to insect sentience, agroecology, and agronomy. We have reached out to preliminary contacts to solicit their input on our research goals. Later, we will survey a wider group of experts for their opinions on the insecticidal mechanisms that are likely to be least painful. This will be an external check for the results of our literature review on insecticide modes of action.The survey will also help us to gauge academic interest in the humane insecticides program, and in insect welfare more generally.

We will continue this research as our primary near-term intervention research project in 2019, and will be providing regular updates on our progress, including after we conduct our first survey.


AVMA Panel. 2013. AVMA Guidelines for the Euthanasia of Animals: 2013 edition. American Veterinary Medical Association.

Carere C, Wood JB and Mather J. 2011. Species differences in captivity: where are the invertebrates? Trends in Ecology & Evolution. 26(5):211.

Chittka L and Niven J. 2009. Are Bigger Brains Better? Current Biology. 19(21):995-1008.

Eisemann CH, Jorgensen WK, Merritt DJ, Rice MJ, Cribb BW, Webb PD and Zalucki MP. 1984. Do insects feel pain? A biological view. Experientia. 40(2):164-167.

Elwood RW. 2011. Pain and Suffering in Invertebrates? ILAR Journal. 52(2):175-184.

Horvath K, Angeletti D, Nascetti G and Carere C. 2013. Invertebrate welfare: an overlooked issue. Annali dell'Istituto Superiore Di Sanita. 49(1):9-17.

Klein C and Barron AB. 2016. What insects can tell us about the origins of consciousness. PNAS. 113(18):4900-4908.

Lockwood JA. 1987. The Moral Standing of Insects and the Ethics of Extinction. The Florida Entomologist. 70(1):70-89.

Mason GJ. 2011. Invertebrate welfare: where is the real evidence for conscious affective states? Trends in Ecology & Evolution. 26(5):212-213.

Mather JA. 2001. Animal Suffering: An Invertebrate Perspective. Journal of Applied Animal Welfare Science. 4(2):151-156.

Perry CJ, Barron AB and Cheng K. 2013. Invertebrate learning and cognition: relating phenomena to neural substrate. WIREs Cognitive Science. 4(5):561-582.

Smith JA. 1991. A Question of Pain in Invertebrates. ILAR Journal. 33(1-2):25-31.

Sneddon LU, Elwood RW, Adamo SA and Leach MC. 2014. Defining and assessing animal pain. Animal Behaviour. 97:201-212.

Sparks TC and Nauen R. 2014. IRAC: Mode of action classification and insecticide resistance management. Pesticide Biochemistry and Physiology. 121:122-128.

Strausfeld NJ and Hirth F. 2013. Deep Homology of Arthropod Central Complex and Vertebrate Basal Ganglia. Science. 340(6129):157-161.

Wigglesworth VB. 1980. Do insects feel pain? Antenna. 1:8-9.

Hollis Howe