Aeshnidae

FAMILY AESHNIDAE

“Hawkers” or “Darners”

The adult Aeshnidae has many air sacs arranged throughout the body, with many thoracic air spaces likely for muscle growth. Preliminary estimates indicate that over 50% of the volume of the specimen is air, either tracheal or in air sacs (Herhold et al., in prep.). Many major tracheae lead into and out of large air sacs, both in the thorax and abdomen, such that determining tracheal pathways and assessing homology is challenging. Most notably, the abdomen possesses four paired longitudinal trunks, a condition not seen in any other insect in this study. This unusual morphology of the adult relative to other winged insects suggested that some of these features may be holdovers from the aquatic immature stage, so a naiad was collected and scanned.

To facilitate differentiation of tracheae and tracheated air sacs in the plates and figures for the adult, a subset of the air sacs that serve as tracheal pathways are shown in orange and tubular tracheae are shown in yellow, and the specimen body outline in transparent gray (as in other plates and figures). Although the tracheae are presented as if “on top” of the air sacs, they are located deeper inside the body. The inset image in the plates shows all air spaces (tracheae and air sacs) in gray; readers are encouraged to refer to the 3D models in the supplementary digital data, where air sacs, tracheae, and tracheated air sacs can be viewed separately or together interactively.

X-ray cross sections from CT scan data indicate the likely presence of flow-directing valves between some air sacs and tracheae in the adult, particularly in the thorax and abdomen (see fig. 29). Air-sac flow-control valves have been documented in Diptera by Wasserthal et al. (2018), and further research into these structures is needed in Odonata.