Migration Isn't Just For The Birds

 

Wandering Glider dragonflies do more than wander...

Most people who are interested in nature know that each spring many species of birds migrate north, and each fall they migrate south.  But birds aren’t the only animals that participate in this amazing natural phenomenon, as even some insects (other than the well-known Monarch butterfly) participate in long-distance migrations as well.  While insects are the most species-rich and abundant group of macroscopic organisms on the planet, understanding many aspects of their annual cycles and behavior drastically trails behind the ability to identify and classify them. 

Migration is defined as the cyclical travel of an animal as it returns to its place of departure.  It can be accomplished in one or multiple generations.  Some animals don’t migrate at all, and others move only short distances south or north.  While the guiding factors for navigation are still being discovered, migration is typically triggered by local climate, food availability, seasonality, or reproduction.

Adult Common Green Darner

Interestingly, about nine dragonfly species are known to migrate, including the Common Green Darner (Anax junius), Wandering Glider (Pantala flavescens), as well as some species in the Skimmer family such as meadowhawks and saddlebags. These dragonflies are known to travel up to 1500 miles over the full cycle of their migration, taking three generations.

Adult Wandering Glider

The secrets of dragonfly migration were discovered and confirmed by biologists measuring the chemical makeup of their wings.  In their immature or nymph stage, dragonflies grow their wings while still developing in local water.  Because the stable hydrogen isotope concentration varies in concentration by latitude, biologists can estimate the geographic region where adult dragonflies developed as nymphs.  

The female Common Green Darner (bottom) is held by
the male (top) after mating, when ovipositing in water.

From February to August the first generation emerges in the south and migrates north.  From June to October the second generation emerges in the north and migrates south.  Both of these generations have the ability to undergo rapid development from egg to adult.  But from November to March the third generation emerges in the south and is non-migratory, focusing mainly on producing another first generation for the cycle to start again.  It is this generation that employs a different strategy, developing slowly in late fall, entering diapause or actively induced dormancy over the winter, and emerging in early spring.

Dragonfly migration was not well understood until very recently.  Research published in 2018 detailed the journeys of Common Green Darners by analyzing 852 wing samples from eight different countries and utilizing 21 years of citizen scientist observations to link each specimen to its place of origin and establish its migration history. However, it is important to note that the timing of migration and the development of nymphs are both highly temperature dependent, so continued climate change could lead to fundamental changes in the migration cycles for dragonflies and other migrating insect species. So as you can see, migration isn’t just for the birds!

Late Summer Skimmers

The quiet waters of a pond like this make great dragonfly habitat

Dragonflies are conspicuous visitors to various bodies of water, especially in the warmer months of the year.    These visitors include members of the largest family of dragonflies, the Libellulidae, otherwise known as the skimmers. Skimmers can be large and colorful, some with distinctive wing patterns, and are often seen perching on twigs and branches.  In late summer, especially after summer rains, some locally common but not often observed species can be found around newly refilled ponds, including the Gray-waisted Skimmer (Cannaphila insularis), Needham’s Skimmer (Libellula needhami), and Slaty Skimmer (Libellula incesta).  

Found in shady or marshy ponds, typically with tall reeds or cattails, the male Gray-waisted Skimmer has greenish-blue eyes, a white face in front and metallic blue on top, and a dark brown or black thorax divided by several pale stripes.  Its abdomen is pruinose gray on the front half and black on the back half, and its wings are clear with extreme dark only at the tips.  Females and juveniles have a yellow-orange abdomen marked with dark brown or black.  Gray-waisted Skimmers are often found perching in the shade at the tips of vegetation, with their abdomen held nearly parallel to the perch.

Gray-waisted Skimmer, male

The male Needham’s Skimmer has reddish-orange eyes and face, and a thorax than is orange in front and paler or more tannish on the sides. Its abdomen is reddish-orange with a dark dorsal stripe down the length, and its orange wings are somewhat darker along the leading edge.  Females and juveniles have brown eyes and faces, a yellowish-brown thorax, and their abdomens are yellow with a dark stripe running down the middle.  Needham’s Skimmers are typically found perching low on vegetation or overhanging the water’s edge.

Needham's Skimmer, male

Most often seen around marshy forest ponds, the male Slaty Skimmer has dark eyes and a metallic blue or violet face, and both the thorax and abdomen have an overall slaty-blue pruinescence.  The wings are typically clear, but can have a pale bluish stripe along the leading edge.  Females and juveniles have red-over-gray eyes and a pale face, a cream-colored thorax with broad dark shoulder stripes, and a black abdomen with yellowish-orange markings. Females also have more prominent dark wing tips and develop a pale pruinosity at maturity.  Males perch on top of tall grasses and sticks most often in sunlit areas.

Slaty Skimmer, male

Check out your local pond or body of water before the end of September, and you just might be rewarded with a sighting of these less common, late summer skimmers!

Summertime Skimmers

The female Comanche Skimmer looks very different from the male (pictured below).

The heat of the summer is often a good time to search for dragonflies, specifically the skimmers, which comprise the largest family of dragonflies.  They are generally the most obvious, too, as they are frequently seen around ponds lakes, and streams, and perch conspicuously on twigs, bushes, and branches. 

Skimmers are often large and colorful with distinctive wing patterns, and many species of skimmers are sexually dimorphic, meaning the males and females of the same species are different in appearance.  Males frequently develop pruinescence or exhibit a frosty or dusty-looking coating when mature, while most females have little to no pruinescence at maturity.  In our area, some of the less common species include the Gray-waisted Skimmer (Cannaphila insularis), Checkered Setwing (Dythemis fugax), Needham’s Skimmer (Libellula needhami), and Comanche Skimmer (Libellula comanche).

The male Gray-waisted Skimmer has greenish-blue eyes, a face that is white in front and metallic blue on top, and a dark thorax divided by several pale stripes.  The wings are clear except for dark extreme tips, and the abdomen is black on the back half and pruinose gray or white on the front half, which gives rise to its common name.  Females and juveniles have reddish-brown over blue-gray eyes, and the abdomen is yellow or orange with brown or black in between segments.  These skimmers prefer shady, marshy ponds, lakes, and streams, particularly those with cattails or tall reeds, and are on the wing from June to September.

Gray-waisted Skimmer, male

From mid-April to mid-December, you can find Checkered Setwings, as they are widely distributed and sometimes locally abundant.  The male has bright red eyes and face, a reddish-brown thorax with obscured dark stripes, and clear wings except for a large patch of brown coloring near the base.  The abdomen is black with two pairs of pale streaks at the base of each segment, giving it a checkered black-and-white appearance. Females and juveniles are similar, but often have a paler face and a pale thorax with narrow dark stripes.  These setwings favor slow-flowing streams and rivers, ponds, and generally open areas with tall vegetation but little canopy.

Checkered Setwing, female

Male Needham’s Skimmers have reddish-orange eyes and face, thorax orange in front and paler on sides, and wings that have orange veins along the leading edge and clear along the trailing edge, giving them a somewhat bicolored appearance.  The abdomen is reddish-orange with a dark dorsal stripe down its length.  Females and juveniles have brown eyes and a pale face, yellowish thorax, and abdomen yellow throughout with the same dark dorsal stripe as the male.  On the wing from late April to early October, this skimmer prefers marshy ponds and lakes, and is often found perching low on vegetation surrounding or overhanging the water.

Needham's Skimmer, male

Comanche Skimmers can be found on the wing from May to mid-October, around springs, seeps, and sluggish areas of clear-running streams.  The male has aqua-blue eyes, a white face, and both thorax and abdomen with a uniformly blue pruinescence.  The wings are clear but for a bi-colored black and white pterostigma, a group of specialized cells in the leading edge of the wing towards the wing tip.  Females and juveniles have reddish-brown to pale blue eyes and a pale face, a cream-colored thorax with broad dark shoulder stripes, and a mostly yellow abdomen with a broad dark dorsal stripe running down the length.

Comanche Skimmer, male

Brave the heat during these hot months of the year and take a walk around a pond, stroll along a stream, or be on the lookout when on the lake, because you just might see one of these interesting summertime skimmers!

Evening Chorus

Green Tree Frog

From late winter into early summer, many of the night sounds you hear are not insects at all, but members of a wide-ranging group of cricket, tree, chorus, and chirping  frogs.  This group of frogs and their allies have adaptations that reveal their mostly arboreal lifestyle, such as forward-facing eyes for binocular-like vision, adhesive pads on their fingers and toes, and a fondness for eating insects.  Often not seen due to their diminutive size, these frogs are commonly mistaken for insects, due to their ability to produce loud and varied mating calls.  Known as ‘advertisement calls’, these calls are produced by the males to attract females and warn other rival males during the breeding season.

Blanchard's Cricket Frog

At ½ to 1 ½ inches, Blanchard’s Cricket Frog (Acris crepitans blanchardi) is found throughout most of the state, except for the Panhandle and West Texas.  Gray to green-brown, this frog has a long rounded snout, dark bands behind its limbs, and a distinguishing triangular patch behind the eyes that points down its back. Diurnal and active all year, these frogs prefer shallow but permanent ponds with vegetation and full sun.  Often seen basking during the daytime, they will jump quickly into the water or away when disturbed, and are capable of covering 6 feet in one leap!  Although they are part of the tree frog family, they are much more terrestrial and are excellent swimmers.  When chorusing, especially at night, the male’s call sounds like clicking small rocks or pebbles together.  Mating occurs in late spring, with the female laying one egg at a time on submerged vegetation.

Green Tree Frog

The Green Tree Frog (Hyla cinerea) is a common, 1 to 2 inch frog with a slender, bright green body, cream-colored belly, and white lips that extend into lateral stripes along the sides of its body.  Found in the eastern third of our state, this frog walks rather than jumps when on the ground.  It is nocturnal, and prefers wet areas such as swamps, edges of lakes, and stream sides.  During its breeding season from March to October, the males start calling just before dark, and sound like groups of tiny ducks quacking.   Females, which are slightly larger than the males and lack the wrinkled vocal pouch, lay their fertilized eggs enclosed in a jelly envelope attached to floating vegetation.   Influenced by the weather, breeding often takes place during or after a rain.

Cliff Chirping Frog

At ¾ to 1 ½ inches, the nocturnal Cliff Chirping Frog (Syrrhophus marnockii) is found in the cracks and crevices of limestone cliffs.  Mostly green with brown mottling and dark crossbars on its hind limbs, this frog also has a proportionately large head and big eyes.  It can run, leap, and hop, and its flattened body allows it to slip into cracks in the rocks to avoid predators.  Sounding a bit like a shy cricket, the call of the Cliff Chirping Frog is a series of short, clear chirps and trills.  While calls are made throughout the year, they are sharper and clearer when females are present.  From February to December females may lay eggs as many as three times in moist leaf litter or soil, although peak breeding occurs in April and May.  

When you’re out at night from winter to late spring or early summer and near one of our natural areas, sit quietly and in no time you should be able to identify the unmistakable sounds that make up the evening chorus!

Aquatic Apalones

Spiny Softshell Turtle

The genus Apalone is thought to come from the Greek apo meaning ‘separate’ and the Anglo-Saxon alone meaning ‘solitary’, as well as the  Greek apalos meaning ‘soft’ or ‘tender.’  All of these terms apply to the members of this genus, which is comprised of the softshell turtles native to North America.  Turtles of this genus exhibit marked sexual dimorphism, or the condition where the two sexes of the same species exhibit different characteristics beyond their sexual organs.

Females grow to twice the size of males, in terms of carapace or shell length.  In males, the claws on their front feet are longer than those on the back feet, enabling them to better hold on to the female while mating.  In females, the claws on the back are longer, for digging into sandbanks in order to lay her eggs.  Lastly, males have a thicker, stout tail that extends well beyond the edge of its carapace, but the female’s tail is relatively thin and barely extends beyond the carapace.  From a behavioral standpoint, the female is much more solitary, wanders more, and requires deeper water, while the male often congregates with juveniles in sandy shallows and while basking along exposed banks.

Spiny Softshell Turtle

There are two species of softshell turtle in Texas. The more common Spiny Softshell Turtle (Apalone spinifera) is found throughout the state, while the Smooth Softshell Turtle (Apalone mutica) is found only in parts of the eastern two-thirds of the state. The Spiny Softshell’s olive-gray or tan carapace is leathery and flat, and has small spines along the front edge, which explains its species name.  At home in rivers, lakes, ponds, and other bodies of water with muddy or soft bottoms, its spends its time feeding on aquatic insects, fish, and crayfish, basking or floating at the surface, or buried in soft, shallow substrates.  Its long neck and snorkel-like nose allows the turtle to breathe at the water’s surface without having to leave its buried location. Females typically grow to 22 inches, while males top out at 8.5 inches in length.

Smooth Softshell Turtle

The Smooth Softshell’s olive-gray to brown carapace is also leathery and flat, but lacks any spines, bumps, or projections.  This characteristic is reflected in its species name, which means ‘shortened’ or ‘docked.’  It also prefers bodies of water with soft, sandy bottoms, and basks on banks, logs, rocks, or under shallow water with its long nose exposed.  Primarily insectivorous, it will also consume vegetation and small invertebrates and fish.  Smaller than the Spiny Softshell, females grow to 14 inches and males to 7 inches in length.

One odd but amazing fact about softshell turtles is that they are believed to absorb 70% of their oxygen through their skin.  The other 30% comes from pumping water in and out of their pharynx or throats, which contain many tiny projections of tissue with small blood vessels that provide a huge surface area for oxygen absorption.  This adaptation allows them to remain underwater for several hours.  Now that’s one highly aquatic Apalone!