Slave-making ants come in two types: facultative and obligate. The researchers compared three types of slave-making ants to see how they differ. They found that obligate slavemakers are rarer than facultative ones, always have slaves, and have a higher proportion of slaves. They also raid bigger colonies and have bigger slaves. One of the ants previously thought to be facultative is actually obligate. The proportion of slaves in colonies varied, with some having up to 90% slaves. The size of slaves differed between species, with some being significantly smaller than others. This study shows that some ants are dependent on slaves for survival and have special adaptations for raiding and caring for them.