Common Green Darner

Anax junius — the common green darner — is one of the largest and most spectacular dragonflies in North America and one of the most extensively-studied insect migrators in the Western Hemisphere. Adults reach 8 cm body length and 11.5 cm wingspan with apple-green thorax, blue-and-black abdomen (males) or red-brown abdomen (females), large compound eyes that meet at the top of the head (Aeshnidae family-typical), and four large translucent wings. The species is widespread across North America from southern Canada to Panama. The most extraordinary biology is the multi-generational annual migration between northern and southern parts of the range. Hallworth et al. (2018, Biology Letters) used stable hydrogen isotope analysis of wing tissue to definitively trace migration patterns: spring migrants fly north from southern overwintering grounds (Mexico, southern Florida, Caribbean) up to 1,500+ km, breed in Canadian and northern US ponds, and die. Their offspring (summer second generation) emerge from those northern ponds and either stay in the north for one more breeding cycle or migrate further north. The autumn third generation, hatched in late summer, flies SOUTH to overwintering grounds to repeat the cycle. No individual makes the entire round trip — the migration is multi-generational, similar to the painted lady butterfly and the globe skimmer dragonfly. Unlike the truly cosmopolitan globe skimmer (which is panmictic and occurs everywhere), the green darner's migration is North American-specific and connects climatically distinct ponds across the continent. The species is also a voracious predator of mosquitoes — adult green darners are major beneficial insects in mosquito control. Naiads spend 1-2 years in ponds before emerging, and similarly are major predators of mosquito larvae and tadpoles.