Gray Petaltail

 

Gray Petaltail
(Tachopteryx thoreyi)
Photographs by James McCann

Behold the terror of the swamps, that efficient killing machine, by wing and by water:  the dragonfly!  Dragonflies are often misjudged by people who don’t know how important they are to their ecosystem.  Dragonflies do not bite people (well, they can but you really have to irritate them a LOT for them to do it).  In fact, in addition to their jewel-like beauty, they are very beneficial to humankind.  Their prodigious mouth parts, in both their adult and larval forms, are designed to trap and devour insects.  Aquatic larval dragonflies, called nymphs or naiads have lower jaws that can shoot out in 1/100 of a second to catch mosquito larvae (or even a tadpole).  In many aquatic ecosystems without fish, dragonfly larvae are the top predators in the food chain.  (The Order name of Dragonflies, and their cousins the Damselflies, is Odonata, meaning "toothy jaw".)

One of Maryland's most distinctive dragonflies is the Gray Petaltail.  This species, considered rare in Maryland, is very large at 3 inches in length.  Its gray and black coloring provides a very effective camouflage when it perches vertically on tree trunks.  Males will sometimes patrol trees, flying up and down the trunk looking for females.  (They may also perch on people wearing brown or gray clothing – which may not be in the dragonfly's best interest since it may freak out the person and end up getting swatted.)  Gray Petaltail males will also frequent sunny clearings to wait for foraging females and defend their territory from other males. 

Gray Petaltail adults can be found from mid-June to mid-August in forested habitats with permanent seepage wetlands; that is, wetlands in which the "wet" part is caused by water percolating through the soil, not from a single point source, like a spring.  In Maryland, they are restricted to counties from the western shore to eastern Allegany County (Upper Coastal Plain, Piedmont and Ridge and Valley physiographic provinces).  The larvae of most dragonfly species are aquatic; they live in some form of water body, be it pond, bog, stream or river.  The Gray Petaltail however is different.  This is the only eastern dragonfly species whose larvae may not be truly aquatic.  They live buried in the mud of seeps, so the quality of the seep is very important.  Indeed, dragonflies are often used as indicators of wetland health and water quality.

Gray Petaltails are terrific dragonflies to study, since they often sit quietly and make excellent photographic subjects.  This is unfortunate as it makes them targets for collectors.  But once they start to move, look out!  The top speed of this and other large dragonflies can reach 60 miles an hour.  Petaltails (both the western Black and our own eastern Gray) can be distinguished from most other dragonfly groups by their widely separated eyes.  In most other groups, the eyes either meet at the top of the head or are only slightly separated.  It is this arrangement of large eyes on top of the head which allow dragonflies a 360 degree view of their world.  Up to 80% of their brains are dedicated to interpreting information from their eyes, but oddly enough, they don't see detail very well.  Their primitive compound eyes, which may have up to 30,000 lenses, specialize in seeing movement.  Very important when you are dining on the wing.

Gray Petaltails are part of the Petaluridae Family.  This family is considered one of the most ancient of dragonfly families, and is at least 150 million years old.  If we can conserve their habitat and protect water quality, there's no reason they won't stick around for another 150 million.