So while I was just browsing the internet I found this study about hunting success in dragonflies. The spangled skimmer dragonflies (Libellula cyanea) were wild-caught but then housed in a large greenhouse-style enclosure with dimensions of 7.3×7.3×4.6 metres for the duration of the study. The greenhouse contained shrubbery and artificial ponds (as well as camera banks for photographing the insects hunting) and was enclosed by wide mesh screening that allowed natural light, air currents and small prey to enter the enclosure. This natural small prey was supplemented with fruit flies that were released and encouraged to stay in the enclosure with piles of rotting fruit. However, I couldn't see any information regarding how many dragonflies were in the enclosure at one time.
The study, which includes an image of the enclosure, is included below:
Linking biomechanics and ecology through predator–prey interactions: flight performance of dragonflies and their prey
The study, which includes an image of the enclosure, is included below:
Linking biomechanics and ecology through predator–prey interactions: flight performance of dragonflies and their prey