Propodeum

The propodeum is the first abdominal segment in insects of the order Hymenoptera (ants, bees, wasps), where the abdomen is narrowly joined to the thorax. It is also referred to as the first abdominal somite, but it is fused to the metathorax and is technically part of the thorax, forming the apparent posterior part of the mesosoma (the middle section of the body). Because of this fusion, the apparent "waist" or petiole in many Hymenoptera occurs after the propodeum. The propodeum often bears characteristic features like spines, tubercles, or a declivity which are used in taxonomic identification. The spiracles, external openings of the respiratory system, are located on the propodeum.