Should we protect insects, shrimp, crabs, and other invertebrates from suffering? The science is uncertain but the stakes are enormousâinvertebrates may outnumber all vertebrates in suffering by orders of magnitude.
Invertebratesâanimals without backbonesâmake up roughly 97% of all animal species and an even greater proportion of all animal individuals. If invertebrates are capable of suffering, then the total amount of suffering in the world is vastly larger than welfare advocates typically consider.
The central question is not merely "can invertebrates detect damage?" (almost certainly yesâthis is nociception). The harder question is: "does damage detection involve subjective sufferingâis there 'something it is like' to be an injured insect or shrimp?" This requires consciousness, which is far harder to establish.
Strongest evidence for sentience among invertebrates. Complex nervous system (500M neurons), sophisticated behavior, learning, play, individual personality. UK law explicitly recognizes their sentience. EU lab animal protections apply. Welfare science consensus: treat as sentient.
LSE 2021 review concluded with confidence that decapods are sentient. Strong behavioral evidence: wound-directed behavior, analgesic effects, trade-off learning. UK Animal Welfare (Sentience) Act covers decapods. Boiling live lobsters banned or restricted in several jurisdictions.
Simpler nervous systems than larger crustaceans but show nociceptive behaviors, sensitization, and some learning. 300-400 billion killed annually in aquaculture. The Shrimp Welfare Project treats them as sentient given uncertainty and scale. Welfare science: precautionary protection warranted.
Strongest evidence for insect sentience. Show pessimistic cognitive biases after stress (Bateson et al., 2011), demonstrate apparent emotions, have neonicotinoid-disrupted pleasure-seeking, and display complex learning. Lars Chittka's work on bee consciousness is influential. Precautionary protection increasingly advocated.
Evidence is mixed and species-dependent. Fruit flies (Drosophila) show nociception and some sensitization. Cockroaches demonstrate learning. But the gap between nociception and subjective suffering is unclear. Most researchers suggest uncertainty demands caution in high-scale use contexts.
Very simple nervous systems with no centralized brain. Current evidence suggests bivalves likely lack the neural substrates for conscious pain, though they have nociceptors. Many utilitarian philosophers (Peter Singer) consider them probably not sentient. Some vegans include them in diet for this reason.
Given genuine scientific uncertainty, how should policy respond? The philosophical literature offers several frameworks:
When evidence is uncertain and potential harm is significant, err on the side of protection. Applied to invertebrates: treat species with meaningful evidence for sentience as sentient until proven otherwise. Cost of unnecessary protection (small) < cost of unnecessary suffering (large). This is the position of the Shrimp Welfare Project and most welfare scientists working on invertebrates.
Multiply estimated probability of sentience by scale of use to get expected welfare impact. Even at 1% probability of bee sentience, 7 trillion bees killed per year represents enormous expected harm. This "expected value" approach drives much of the EA-adjacent invertebrate welfare work.
Different levels of certainty warrant different levels of protection. Cephalopods â full protection equivalent to vertebrates. Decapods â significant protections (humane killing methods, ban on live boiling). Insects â basic protections only in high-volume contexts where marginal cost is low. Bivalves â no specific protections currently warranted.