Research summary - Farmed yellow mealworm welfare (Rethink Priorities)

As of 2020, around 300 billion yellow mealworms (Tenebrio molitor) are farmed annually (though recent estimates now put this figure at over 3 trillion individuals (Pells, 2023)).

Barrett et al. 2023 is the first publication to consider species-specific welfare concerns for farmed mealworms.

The authors identify 15 current and future welfare concerns, including more pressing current concerns such as:

• Disease — Bacterial, fungal, protist, and viral pathogens can cause sluggishness, tissue damage, slowed growth, increased susceptibility to other diseases, and even mass-mortality events.
• High larval rearing densities — Density can cause a range of negative effects, including increased cannibalism and disease, higher chances of heat-related death, competition over food leading to malnutrition, and behavioral restriction near pupation.
• Inadequate larval nutrition — This may result from not providing enough protein in the animals' largely grains-based diet.
• Light use during handling — Photophobic adults and larvae may experience significant stress due to light use during handling.
• Slaughter methods — While we have high empirical uncertainty about the relative harms of slaughter methods, it is clear that some approaches to slaughter and depopulation on farms are more harmful than others.

Future concerns that haven't yet been realized on farms include:

• Novel, potentially toxic, or inadequate feed substrates — Polymers (like plastics) and mycotoxin-contaminated grains may be more likely to be used in the future.
• Selective breeding and genetic modification — In vertebrate animals, selective breeding has caused a large number of welfare issues. The same might be expected to become true for mealworms.