Songs of Stridulation

 

Immature katydids, called nymphs, are initially wingless. 

As the summer temperatures heat up, songs of singing insects fill the air with a variety of sounds.  Members of the order Orthoptera, including katydids, crickets, and grasshoppers, produce a variety of sounds through stridulation, or the rubbing of one body part against another.  

Differential Grasshopper, Melanoplus differentialis

While grasshoppers typically stridulate by rubbing their hind legs against their closed wings, katydids and crickets have modified bases of their wings in order to produce sound.  Specifically, they have a sharp edge or ‘scraper’ on the upper surface of the hindwing which they rub against a row of bumps or ‘file’ on the underside of the forewing. During sound production, katydids and crickets elevate their wings and move them rapidly back and forth, and the wings vibrate as a result of the scraper rubbing against the file.

Central Texas Leaf-Katydid, Paracyrtophyllus robustus

Unlike Orthoptera, male Cicadas in the order Hemiptera produce sounds through a pair of special ribbed organs or ‘tymbals’ located on sides of their abdomens, just behind their wings. When they contract their muscles, it causes the ribs to bend suddenly, producing a sound that resonates within a large air sac in their abdomen. The distinctive sound that is produced is one of the loudest made by any insect.

Resh Cicada, Megatibicen resh

The use of sound is crucial in courtship, with each species having its own distinct song.  Males attract mates through stridulation, producing a vibration frequency that is species-specific.  Songs are distinguished both by their dominant frequency and the details of their timing patterns. Crickets generally produce musical trills of continuous notes often too fast to count, or short bursts of chirps followed by silence.  

Field Cricket, a species in the Gryllinae family

Katydids and grasshoppers have high-pitched songs, composed of atonal shuffles, rattles, scrapes, buzzes, or ticks.  Some sing more or less continuously while other species have long silences in between periods of singing.  Cicada songs are the most penetrating, as rattling buzzes or harsh trills, often with a pulsating or grinding quality.

Fork-tailed Bush Katydid, Scudderia furcata

While most insect songs are the calling songs of males intended to attract females, these songs are thought to have other functions as well.  Some songs are for courtship once a mate is found, and some serve to attract males to a group chorus or to keep males optimally dispersed within a singing colony.  Aggressive songs can also be heard, when two males encounter each other, or even disturbance calls, when an insect is touched or handled.  Whatever the reason, now is the season to hear the songs of stridulation!

Mariposa de la Muerte

Commonly known as owlet moths, cutworms, or armyworms, moths in the Noctuidae family make up one of the largest families of Lepidoptera.  The word Noctuidae is derived from the Latin word noctua meaning ‘little owl’ and the largest moth in this family in the continental United States is the Black Witch (Ascalapha odorata).

The Black Witch moth has been known as mariposa de la muerte or ‘butterfly of death’ since the time of the Aztecs, when it was believed that they were harbingers of death.  With a wingspan of up to 6 inches, its upperside is mottled dark brown to grayish-brown with hints of iridescent purple and pink, and females, which are slightly larger and lighter in color than males, have a pale almost lavender-pink median band through both fore and hind wings.  

A Black Witch (male) attracted to our mercury vapor light

Common to abundant in the New World topics as far south as Brazil, the Black Witch flies year-round in south Florida and the Rio Grande Valley of Texas.  In June and July, summer monsoons in Mexico trigger this fabulous creature to migrate north through Texas, where it is often found roosting in garages, under eaves, or under bridges.  It has the ability to migrate great distances over bodies of open water, such as the Gulf of Mexico, and one specimen was recorded in 1903 in Leadville, Colorado, caught in a snowstorm on the Fourth of July!

Primarily nocturnal, the adult Black Witch is attracted to light and fermenting fruit.  Its larvae feed at night on a variety of cassias, acacias, ebony, mesquite, and other woody legumes, and rest during the day hidden under bark and branches.  Up to 3 inches long, its caterpillar is dark gray tinged with brown, with a pale stripe down the back and dark stripes down the sides, and it relies on this natural camouflage to make it difficult to spot.  Pupation occurs on the ground in scattered leaf litter within a fragile cocoon.  Black Witches breed year round in overlapping generations, and their adult stage is thought to last only three or four weeks.

A Black Witch (female) perched above our front door!

At first glance, this very large moth is often mistaken for a small bat hovering around a porch light, but it will eventually land and linger for several hours if undisturbed.  If this happens to you, you can only hope that the South Texas legend of the Black Witch is true, as it states, “If a Black Witch lands above your door and stays there for a while, you could win the lottery!”

It's a Sphinx, Methinks!

A White-lined Sphinx hovers while feeding at a thistle

A family of moths called the Sphingidae are more commonly known as hawk moths, hummingbird moths, and sphinx moths.  This family has over 1,450 species worldwide, and 73 of them are known to be present in Texas.  Generally speaking, these moths are named not just for their streamlined bullet-shaped bodies that have long narrow forewings and short hindwings, but also for their distinct behavior which comes in the form of swift, hovering flight.  Many species in this family hover in mid-air or swing from side to side when feeding on flowers, an ability that has evolved in only three other groups: hummingbirds, certain bats, and hoverflies.  In addition to nectaring on flowers, these moths often pollinate them at the same time.  

The leaf-feeding caterpillars or larva of these moths typically have a smooth body with a characteristic horn near their posterior end, hence the common name hornworm.  They pupate in an earthen cell or loose cocoon at or near the soil surface.  The word sphinx was first associated with the larva in 1736, when Rene Reaumur, a French scientist and entomologist, noted that they often assumed a pose reminiscent of the mysterious Egyptian Sphinx of antiquity.  They accomplish this pose by holding their anterior legs off their substrate and tucking their heads underneath when resting, which appears to form an upright praying position.  

Vine Sphinx

White-lined Sphinx

In our area, some of the more interesting sphinx moths include the Vine Sphinx (Eumorpha vitis), Tersa Sphinx (Xylophanes tersa), Waved Sphinx (Ceratomia undulosa), and Rustic Sphinx (Manduca rustica).  The Vine Sphinx appears similar to the well-known White-lined Sphinx, but is dark greenish-brown with a more complex pattern of sharp whitish streaks and bands on its forewings (instead of an even, pale tan stripe from base to tip intersecting uniform white lines) and a small pinkish patch on its hindwings (instead of a broad pink band).  The wingspan of this moth is 3.5 to 4 inches, it flies from April to May and July to October, and the larva feed on grapevines.  

Tersa Sphinx

The Tersa Sphinx is easily identified by its long pointed abdomen, brownish-tan forewings that look like woodgrain, and hindwings with jagged black and white markings.  This sleek, fighter jet-like moth has a wingspan of 2.5 to 3 inches, flies June to October, and its larva feed on catalpa and smooth false buttonweed.

Waved Sphinx

The Waved Sphinx has brownish-gray forewings with contrasting black streaks and zigzag lines and a small, kidney-shaped white spot outlined in black, while the hindwings are gray with darker gray shading.  Its wingspan is 3 to 4.5 inches, it flies from May to October, and its larva feed on ashes and oaks.  

Rustic Sphinx

The Rustic Sphinx has an abdomen with three pairs of yellow spots along the sides, and yellowish to chocolate-brown forewings with black zigzag lines. It has a wingspan of 3.5 to 6 inches, flies from July to October, and its larva feed on crossvine and trumpet vine. 

Certain species of sphinx moths have been widely used in scientific research aimed at better understanding animal flight and insect physiology.  Some have played a key role in advancing knowledge of hormones produced by nerve cells, while others have contributed to the development of small flying robots by shedding light on how these insects stay airborne while hovering.  Those are some pretty important roles for a sphinx, methinks!