Are glue traps cruel

Answer 1

That would depend on the type of glue trap, the species trapped and what ensues after being trapped.

Glue traps do not kill the animals that are trapped on there. All they do is trap live animals with adhesive materials. Their "humaneness" or "cruelness" depends on their usage.

Mammals/Reptiles/Birds

Undoubtedly, using a glue trap on a mammal/reptile/bird (such as a rat, gecko or snake) and leaving them to starve is a form of animal cruelty. Like humans, other mammals have nociceptors (pain receptors), a limbic system and a neocortex, the parts of the brain that account for conscious emotions and experiences such as suffering. Birds and and arguably reptiles possess a homolog to it, meaning that sentience in these animals is likely. When trapped, the trapped animal will likely experience at least some distress from not being able to move away. If the trap is disposed without killing the animal or left unchecked for too long, the trapped animal will starve to death. This will cause the animal unjustifiably extreme distress and suffering for unusual periods of time. They will likely also injure themselves trying to struggle free from the traps. It would be like if someone glued your hands and legs to the floor and then just waited until you starved to death. Some glue trap manufacturers apply eugenol to their traps, under the assumption that it acts as a sedative, though there are reports that it may cause discomfort if not injected directly into the bloodstream. If one must use a glue trap, it is possible to kill the trapped animal humanely (for example, by smacking them on the head with a mallet with great force to kill them instantly) or to free them using vegetable oil. Regardless, it is certainly not the most humane option to use on vertebrates.

The American and Canadian governments advise against their use (albeit not for animal welfare reasons), as trapped animals may urinate/defecate and/or bleed if injured trying to escape, which could expose users to disease-causing agents. Ireland and New Zealand have banned the use of glue traps for rodents.

Insects

Using glue traps on insects is not thought of to be cruel, as they are not thought of to be able to feel pain. The insect nervous system greatly differs from those of vertebrates in that they do not have a cerebral cortex (or any homolog), a limbic system or nociceptors (with the exception of Drosophila melanogaster). Insect behaviour is largely a result of hardwired reflexes, with limited learning. While an insect may struggle or exhibit escape responses, this is considered a reflex. Insects do not react to bodily injury, for example, if their leg is crushed, they will not limp and instead continue applying it to the ground with undiminished force, and a locust will continue feeding as it is being devoured. Given these criteria, the overall consensus is that insects do not suffer. The New Zealand government's prohibition on glue traps does not apply to insect glue traps, and their use for insects remain uncontroversial.