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Wednesday, August 10, 2011
The first time I saw this dragonfly above, I was convinced I must be looking at a new species, one I’d never seen before at Nature Boardwalk at Lincoln Park Zoo. It turns out this is actually a blue dasher, one of the most common species at the pond. Although I’d counted dozens of blue dashers at Nature Boardwalk, I’d never seen a female! In this species, the females look nothing like the males (below), and apparently they’re a whole lot harder to spot.
The tendency to see many more males than females holds true for several dragonfly species at Nature Boardwalk. Blue dashers take this to an extreme, but in widow skimmers and twelve-spotted skimmers, the same pattern emerges.
So where are all the females? A number of researchers have investigated the skewed sex ratio in dragonflies and damselflies to attempt to answer this question. It’s commonly known that in most types of dragonflies and damselflies, more males are seen than females.
There isn’t a clear explanation for the disparity in sightings. One proposal is that females have less flashy coloration, are better camouflaged and are less bold than their male counterparts. According to this hypothesis, there aren’t necessarily fewer females—females are just better at going unobserved.
Another possible reason is that females may have lower survival than males, but survival rates simply aren’t known in most cases. The bottom line: we don’t yet know why we see more males than females. In any event, this makes it a special treat to see the elusive females dragonflies.
Nature Boardwalk at Lincoln Park Zoo
By transforming the South Pond into Nature Boardwalk, Lincoln Park Zoo has created an urban ecosystem in the heart of the city. Enjoy a virtual view as native plants and animals establish themselves in this rare refuge.
As Lincoln Park Zoo’s director of horticulture, Brian oversees the zoo’s gardens, from bud to bloom.
As coordinator of wildlife management, Mason chronicles the bugs, birds, fish, insects, mammals and more that make their homes at Nature Boardwalk.
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