Defensive biting by Tetragonisca angustula is dangerous but not suicidal.
Suicidal defense is an important and effective attribute of some highly social animals. It has been suggested that the defensive behavior of biting onto raiders is suicidal in stingless bees; however, the mechanisms causing death are unclear. We conducted the first test of the effect of agonistic encounters on death and injury rates of guards of a stingless bee, Tetragonisca angustula, that bit both conspecific and heterospecific invaders within plastic tubes . Tetragonisca angustula guards bit and immobilized invading bees for long durations and had the ability to release their hold, but rarely did so unless the other bee died. In our assays, which lasted hours to up to 1 day, the probability of death during nest defense by T. angustula was 5-7%. Bitten invading bees fought back, often causing injury and sometimes death of the biting T. angustula. Tetragonisca angustula foragers can survive for 7 days without food and so death by starvation of guards during day-long encounters seems unlikely. Death rates of biting guards holding non-nestmates on the ground may be higher in the field due to susceptibility to predation. Defensive biting of stingless bees effectively protects the nest, and most guards likely are able to return to their tasks after a raid is thwarted, though studies in a more naturalistic setting are needed.