The Odonata of Tarrant County

The Odonata of Tarrant County

The Odonata of Tarrant County is a project that has been unlike any of my other work so far. It was put together as an educational display but the images are meant to be able stand aesthetically without the accompanying text.

It is also unique in the way that it is much less emotional and more subject-based than a lot of the photography I tend to gravitate toward. I guess that's what science is. That being said, it is still very personal for me as observing dragonflies has played an interesting role in my life over the years.

[skip to gallery]

Prints and elaborated descriptions of images from this project are available here.

common questions

What do they eat?
Dragonflies are carnivorous. They eat mosquitoes, small flies and other insects. Some dragonflies will eat other dragonflies.
How long do they live?
Adult dragonflies can live from a few weeks up to several months.
How may species are in Tarrant County...Texas...the United States...the world?
There are 85 known species in Tarrant County and around 244 in Texas. In the United States we have around 450 different species and there are more than 5,500 in the world. Dragonflies can fly long distances to disperse themselves and new species are constantly being discovered and re-evaluated with genetic testing so exact numbers are not always able to be established.
Are dragonflies pests?
No! Dragonflies eat moquitoes during both of their life stages. They also prey on other small flies and gnats. They are beneficial insects (to humans) and due to habitat tolerances requiring relatively unpolluted water, some dragonflies species can be used as indicators guaging water quality.
Do dragonflies sleep?
Sort of...most are diurnal, active during the day and resting, or roosting at night. When their active day is over, they find cover and perch in a suspended state, essentially in low-power mode.

terminology/definitions

in tandem
male and female paired (male grasping female with end of his abdomen behind her head)
in copula
when the male and female are forming the wheel position while mating
mate-guarding
evolutionary tactic to secure parental investment
nymph (sometimes referred to as naiad)
larval form of dragonfly, lives in freshwater habitat eating small organisms, molts many times before emerging
obelisking
behavior in which dragonfly changes posture relative to sun, raising abdomen to control surface area/sun exposure (method of thermoregulation)
ovipositing
laying eggs (some lay eggs on surface of water or algae and some deposit eggs inside plant tissues, mud or other substrate on water)
predation
biological interaction where one entity (predator) consumes another (prey)
teneral
stage immediately after emerging, wings and body are soft and glossy, very vulnerable to predation

possibly interesting facts

  • have existed for 300 million years
  • have changed little over that time (though size has decreased, possibly due to lower oxygen percentage in air)
  • are carnivorous and are top aerial predators in insect world
  • you don’t need to whisper around them because they do not have ears
  • cannot sting you—they don’t have anything to sting you with
  • the species Pantala flavescens is found on every continent except Antarctica; it’s extremely short larval period (as short as five weeks) allows it to breed in ephemeral ponds and ditches and quickly establish populations

about this project

This project is meant to highlight some of the fascinating and colorful creatures in nature that live parallel right in front of us but mostly go unnoticed. Obviously I’m talking about dragonflies, and all of those featured here are able to be seen in Tarrant County, Texas.

Species were chosen based on their relative representation of families and genera present in our location as well as their unique visual characteristics. Species with obvious sexual dimorphism (visual differences between genders) were preferred. On the physical display each species selected has a placard nearby containing its scientific name, it’s approximate flight season in our area and some points of interest; for the web I haven’t figured out the best way to present this information yet.

There are currently 85 species of Odonata that have been found in Tarrant County (as of January 2018). The order Odonata is subdivided into Anisoptera (dragonflies) and Zygoptera (damselflies). Tarrant County has five different families of Anisoptera further broken down into 33 genera and 57 species in Tarrant County. The local zygopterans are composed of three different families further classified in eight genera and ultimately 28 species.

what are dragonflies?

Dragonflies are insects that have been on Earth for over 300 million years, existing as voracious aerial predators of the insect world. The fossils of relatives of modern-day dragonflies have been found with wingspans over two feet long. As with many other creatures like birds and lizards, dragonflies have since shrunk in size as they have evolved. Setting aside the size differences, the basic body structures of dragonflies have remained relatively unchanged.

The scientific order Odonata is composed of two sub-orders, Anisoptera and Zygoptera. Anisoptera are the generally larger insects that typically hold their wings over their abdomens when at rest. Zygoptera are what we call damselflies; most hold their wings folded over their abdomens when at rest. Zygopterans are generally smaller and less powerful fliers.

Confusingly, in English, the term dragonfly can encompass both sub-orders or just Anisoptera. Unless explicitly specified, dragonfly will refer to both dragonflies (anisopterans) and damselflies (zygopterans) in this text.

life history

In north Texas we typically see dragonflies flying from spring through autumn but they are here year-round. Dragonflies live the larval portion of their life under water in ponds, streams, rivers and other freshwater habitats. Their larval body looks nothing like their adult form.

As larvae dragonflies are important creatures in freshwater food chains as they consume aquatic larvae (notably mosquito larvae) and are themselves food for other creatures such as frogs, fish and even other dragonfly larvae.

They live as larvae for a period of weeks to years (duration will depend on species), molting to grow until they are ready to emerge from the water. Then the dragonflies will molt one final time, inflate their wings, pump the water out of their body and begin the terrestrial portion of their life, as most of us recognize them.

The newly-emerged dragonfly is very shiny and soft, vulnerable to predation—during this phase it is referred to as teneral. The dragonfly’s wings and tissues will harden and the color will set and they then take their maiden flight to cover. They will return to the water when sexually mature to mate and lay eggs.

As adults dragonflies consume mosquitoes and other small insects. They typically live between weeks and months depending on the myriad of factors that can contribute to their deaths. They are predated upon by frogs, fish, birds, snakes and sometimes other dragonflies.

morphology

Like all insects, dragonflies are made up of a head, a thorax and an abdomen.

The head contains powerful mandibles (mouth parts) used to tear apart prey. The mandibles move side-to-side and have long bristles on them to help catch and retain food. The head also features the dragonfly’s large compound eyes, which can be made up of tens of thousands of individual lenses.

The thorax is the middle body portion between the head and the abdomen. The thorax houses a dragonfly’s robust flight muscles, its wings and their six legs. The wings are sturdy but flexible and capable of beating independently, which is why dragonflies are capable of such incredible flight maneuvers. The legs are not a primary means of locomotion as adult (flying is) but they have long, sharp spines on them which are helpful for catching on twigs/other perches when landing, as well as scooping up and grasping prey. The sides of the thorax often contain marks useful for species identification.

Dragonflies have an abdomen, not a tail. The abdomen is made up of 10 segments and has terminal appendages which differ on males and females.