Arthropods 10

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Southern California Arthropods (Mostly) #10: Lacewings (Order Neuroptera)
© W.P. Armstrong 15 April 2009
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The Neuroptera is a large order of fascinating insects, including about 6,000 species worldwide. They are often called the "nerve-winged insects" because of the elaborate pattern of longitudinal and cross-veins (nerves) in the four wings of adults. These insects undergo complete metamorphosis with an egg, larva, pupa and winged adult. The larval stage is often a grotesque, wingless creature with long, sicklelike jaws. Pupation usually occurs in a silken cocoon; however, the silk is not derived from modified salivary glands as in most insects, but is produced by the Malpighian tubules and is spun from the anus. The order includes many predaceous, night-flying species, including lacewings, alderflies, snakeflies and dobsonflies. The immature or larval stage of dobsonflies, called hellgrammites, are familiar to fishermen because they are commonly used as bait. One curious member of the order, called a mantispid, shows a striking resemblance to a miniature preying mantis with enlarged, grasping front legs.


Snakeflies (Family Raphidiidae)

A female snakefly (Agulla sp.) with a long ovipositor.

This beneficial predatory insect is related to lacewings, dobsonflies and antlions. The adult feeds on small, soft-bodied insects, including aphids, scale insects and mites (arachnids).

A female snakefly (Agulla sp.) photographed in San Marcos, CA 29 April 2012.
Nikon D-90 with 60mm Micro Nikkor AF-S F/2.8G ED & Phoenix Ring Flash Flash


Green Lacewings (Family Chrysopidae)

The common green lacewing (Chrysoperla plorabunda). This delicate, beneficial insect is commonly attracted to porch lights during the warm summer months in southern California. The larvae are called "aphid lions" and have a voracious appetite for aphids. In fact, the eggs are placed on silken stalks, out of the reach of the hungry larvae.


Dobsonfly (Family Corydalidae)

California dobsonfly (Neohermes californicus). The larvae are called hellgrammites.

Male eastern dobsonfly (Corydalus cornutus) phtographed in Tennesee. Note the enlarged mandibles.


Moth Lacewing (Family Ithonidae)
Rare Insect Discovered in Anza-Borrego Desert State Park

The North American genus Oliarces contains only one species, O. clara. It was discovered in1908 near Mecca, California approximately 13 kilometers northwest of the Salton Sea. The original type locality, called Walter's Station, was an early watering stop for steam locomotives along the Southern Pacific Railroad. It was not collected again until 1949 near Earp, California (Parker Dam area). Since then, a few collections have been made near Yuma, Arizona; Telegraph Pass in Yuma County, Arizona; near Palm Springs and Deep Canyon in Riverside County; near Glamis in Imperial County, California; road between Rice and Blythe, California; and Boulder City, Nevada. A recent discovery by James Dillane in South Palm Wash on 10 April 2009 is the first documented location for San Diego County. I revisited the slot canyon above the wash on 16 April 2009 and found one individual clinging to the vertical canyon wall. It is not known whether the adult emerged from the ground in this canyon, or whether it was carried to this sheltered location by strong winds. Special thanks to Alison Oblites for finding the latter individual on the canyon wall.

Deep slot canyon that drains into South Palm Wash.

A moth lacewing (Oliarces clara) clinging to vertical canyon wall.

Seven species in the family Ithonidae have been described, and all of them occur in Australia except for Oliarces clara, a native of the American southwest desert region. Larvae in the wild have only been found associated with the roots of creosote bush (Larrea tridentata). Feeding on roots is unusual for Neuropterans, because most species are predaceous. It is curious why this insect is seldom seen, and yet its host shrub is the ubiquitous creosote bush (Larrea tridentata) that dominates the vast desert region of Mexico and the southwestern United States. More research is needed on this fascinating insect.

Larrea tridentata is a relatively recent colonizer of North America. It first appeared in fossil packrat middens during the late Quaternary, approximately 18,700 years ago. This species likely arrived in North America as a result of long-distance dispersal from South America, and was probably derived from an ancestral population of L. divaricata which is widespread in Argentina, Chile and Peru. Since the last period of glaciation in the United States (12,000 years ago), as warm deserts formed in Mexico and the American Southwest, L. tridentata expanded its range to include the present-day Chihuahuan, Sonoran and Mojave Deserts. During this range expansion, it evolved into different polyploid races: In the Chihuahuan Desert the plants have the normal diploid number (2n=26) like the plants in Argentina. Sonoran Desert plants are tetraploid (4n=52) and those in the Mojave Desert are hexaploid (6n= 78). The extra genetic material in the polyploids may provide more adaptibility, such as survival in colder climates of the Mojave Desert. The oldest creosote bush clone in the Mojave Desert studied by Dr. Frank Vasek at UC Riverside was dated at 11,700 years old. If these colonization dates are accurate, It must have been one of the early creosote bush seedlings in this region.

  • Duran, K.L., Lowrey, T.K., Parmenter, R.R., and P.O. Lewis. 2005. "Genetic Diversity in Chihuahuan Desert Populations of Creosotebush (Zygophyllaceae: Larrea tridentata)." American Journal of Botany 92: 722-729.

It would be interesting to know when the moth lacewing colonized these creosote bush scrub habitats in North American, and whether it also coexists with South American populations of Larrea divaricata. The fossil of a rapismatid-like species of Ithonidae (Principiala incerta) was recently discovered in the lower Cretaceous Crato Formation of northeastern Brazil.

  • Makarkin, V.N., and F. Menon. 2007. "First Record of Fossil 'Rapismatid-Like' Ithonidae (Insecta, Neuroptera) From the Lower Cretaceous Crato Formation of Brazil". Cretaceous Research 28: 743-753.

According to Faulkner (1990), the adults emerge from the soil and mate during a four-day period during mid-April to mid-May. Adults have a wingspan of 35 to 40 mm (1.6 inches). Moth lacewings are reportedly weak flyers and are easy prey for birds and other predator insects. They apparently do not feed as adults and soon die after the mating period. Adult females in captivity lay their eggs on the soil. After the eggs hatch, the grub-like larvae are believed to burrow into the soil and attach to plant roots. For more information, please refer to the following reference by David Faulkner:

  • Faulkner, D.K. 1990. "Current Knowledge of the Biology of the Moth-Lacewing Oliarces clara Banks (Insecta: Neuroptera: Ithonidae)." Advances in Neuropterology. Proceedings of the Third International Symposium on Neuropterology, Pretoria, R.S.A. pp. 197-203.

During their short adult life, moth lacewings apparently find their mates by a phenomenon known as "hilltopping." They simply fly upslope to the summit of the nearest hill or ridge. This method of mating is also used by members of the order Lepidoptera. During the summer months in San Diego County, it is common to find dozens of species of butterflies chasing each other in rather erratic flying behavior at the tops of chaparral-covered hills. These remote mountain tops are popular meeting places for sexually active insects looking for mates.

Moth lacewing (Oliarces clara), a seldom-seen desert species in the family Ithonidae.


Mantispids (Family Mantispidae)

A mantispid (Mantispa sp.): One of the most unusual insects on Wayne's Word.

Like the snakefly, this unusual, predaceous neuropteran feeds on other small, soft-bodied insects. Its raptorial (grasping) front legs resemble those of the preying mantis, except mantids are much larger insects that belong to a different insect order. Although mantids were once placed in the order Orthoptera along with grasshoppers, crickets and cockroaches, they are now placed in the separate order Mantodea. Mantispids occur in southern California, but are seldom seen by casual observers.

A mantispid (Mantispa sp.): One of the most unusual insects on Wayne's Word.

Although the mantispid and preying mantis have evolved morphologically similar traits, including triangular head with large eyes and a pair of raptorial front legs used for grasping prey, they belong to different families in distantly-related insect orders. This is a good example of convergent evolution. Even more amazing is the fact that this mantispid was sitting in a vial of alcohol on a shelf in the Life Science's Department at Palomar College for more than 35 years.

A seldom-seen mantispid photographed in alcohol. This preying mantis look-alike belongs to an entirely different insect order, the Neuroptera. The remarkable resemblance is a good example of convergent evolution. It was collected by Mr. Wolffia at Palomar College in the late 1960s. The body and wings are about 22 mm in length, less than one inch.

Which of these insects is a "preying" mantis and which is a mantispid?
(I prefer "preying" rather than "praying" because I don't think these insects are that religious.)

A small mantispid and a preying mantis, an example of convergent evolution.

The mantispid is much smaller than the preying mantis and has shorter antennae. Mantispids have two pairs of membranous wings with a network of veins (nerves) typical of the order Neuroptera. In fact, the name "Neuroptera" is derived from Greek and means "nerve wing." The wings are held tentlike over the body, unlike the wings of mantids. Mantids have a pair of leathery forewings that lie flat over the abdomen. A pair of membranous hind wings are folded beneath the forewings. Mantispids undergo complete metamorphosis with an egg, larva, pupa and adult. Mantids have incomplete metamorphosis with a egg, nymph (that resembles a miniature adult) and adult.

A female mantispid will lay numerous stalked eggs on leaves and wooden structures. The newly hatched larvae, less than a millimeter in length, begin their genetically-programmed search for spiders. They enter the egg sac of a spider, either through direct penetration, or they climb onto the female spider and enter the egg sac as she builds it. While the mantispid is waiting for the female spider to build an egg sac, it will enter the spider's book lungs and feed on the spider's blood. The mantispid enters the egg sac before the female spider can finish spinning the protective silken case. Once inside the egg sac, the mantispid will dine on spider eggs and grow. The mature larva will then spin a cocoon and metamorphose into a pupa, all of this within the spider's egg sac. It will emerge as an adult a few weeks later.


Antlions (Family Myrmeleontidae)

Antlions belong to the family Myrmeleontidae and include over 600 described species. Two of the most common genera in the southwestern United States are Myrmeleon and Brachynemurus. Like many other members of the order, adult antlions are commonly seen around lights and campfires, particularly during the late summer and fall. They have two pairs of long, narrow, many-veined wings and a long, slender abdomen. Although they greatly resemble small and unrelated dragonflies, called damselflies, they belong to an entirely different order of insects.

The adult antlion can be readily distinguished from a damselfly by its long, clubbed antennae. It is a feeble flier and flutters about through the night air in search of a mate. As in all animals, without the mating imperative, the genes of this remarkable species would be lost forever. The most incredible part of its life cycle begins after the gravid (pregnant) female lays her eggs in the sand, and after the immature larvae hatch from the eggs.

The adult antlion superficially resembles the unrelated damselfly. It can readily be distinguished by its longer, clubbed antennae and nocturnal life style.

Lateral view of adult antlion in resting position.

The arid southwestern United States is rich in diverse forms of animal life, but the larva of an antlion resembles something out of a science fiction horror movie. In fact, a remarkably similar large scale model of it was used in the Star Trek II film, "The Wrath of Khan!" This remarkable creature makes funnel-shaped, crater-like pits in soft sand, and then waits patiently at the bottom to ambush a hapless passer-by that happens to fall in. It is commonly called an antlion, referring to its habit of preying on small crawling insects, such as ants. If antlions were about 100 times larger, they would be a formidable threat to people walking in the desert.

The antlion larva waits patiently at the bottom of its ingenious pitfall trap. It is often called a "doodlebug" by certain people. In fact, some of these people claim that repeating the phrase "doodlebug, doodlebug, come out of your hole" with your face close to the ground will cause the antlion larva to crawl out into view. The Wayne's Word staff has tested this hypothesis repeatedly and we must agree with the conclusions of other scientists that antlions do not understand the word "doodlebug." In fact, they can't understand anything you say. When your speak close to their crater, some grains of sand become dislodged and fall into the pit. Falsely believing it has made a capture, the antlion becomes excited and crawls out into view. This same behavior can be observed in various types of spiders by gently touching their web with a small twig or feather.

Crater-like pits made by the antlion larva in soft sand. Each funnel-like crater is approximately 2 centimeters in diameter and almost as deep.

The antlion larva is a ferocious-appearing creature with a robust, fusiform body bearing three pairs of walking legs and a slender neck. Its small head bears an enormous pair of sicklelike jaws (mandibles) with several sharp, teethlike projections. Like sharp hypodermic needles, the hollow jaws pierce the victim and suck fluids out of its body. According to R.E. Hutchins (Insects, 1966), the jaws are capable of injecting venom which digests and dissolves the body contents of the prey.

Close-up view of an antlion larva showing its fusiform body and large, toothed jaws (mandibles).

In some species, the larva excavates a conical pit in the sand by crawling backwards in circles, at the same time flipping out sand grains with its long jaws. As it moves round and round, the pit gradually gets deeper and deeper. Eventually the crater reaches 2-4 centimeters across and almost as deep, with very steep walls. The slope of the funnel is adjusted to the critical angle of repose for sand, so that the sides readily give way under the feet of a would-be escapee. The larva waits quietly at the bottom of the pit, with its body off to one side and concealed by the steep wall. Only its sicklelike jaws protrude from the sand and often they are in a wide-opened position.

When crawling insects, such as ants, inadvertently fall into the pit it is virtually impossible for them to climb the loose sand on the steep walls. To make matters worse, the antlion quickly flips out more sand, thus deepening the pit and causing miniature landslides along the walls which knock the struggling ant to the bottom. If the ant or other insect is large enough it may escape, but usually its struggle is hopeless when it is seized by the powerful jaws of the antlion. Antlion larvae are capable of capturing and killing a variety of insects, and can even subdue small spiders. Often the struggling victim is pulled beneath the sand as its body fluids are gradually siphoned out. After consuming all the contents, the lifeless, dry carcass is flicked out of the pit, and the pit is readied for a new victim.

Antlion pits are very common in sandy washes and riverbeds. They are especially abundant in soft sand beneath trees, such cottonwoods and willows, or under overhanging rocks. In some places they are so numerous that they resemble miniature craters on the surface of the moon. Apparently the larvae prefer dry places that are protected from the rain.

The larvae are relatively easy to catch and maintain in captivity. Although they look ferocious, they pose no serious threat to humans. They are much too small to bite your fingers or drag you into their sand pit. When disturbed, the larva usually remains motionless. It is covered with a layer of dust or sand and is easily overlooked. All you need is a container of soft, dry sand and an ample supply of small, crawling insects for food. We have raised antlion larvae in glass bowls at Wayne's Word and have observed all the intimate details of their entire life cycle. We once had an entire antlion "condominium" in a large plastic tray, that is, until a cat decided to use it for a litter box. Antlions will also be at home in a bowl of sugar or salt, and make their usual circular pits. Sometimes they tend to get a little messy as they flick sugar all over the table top. It is very startling to guests when they reach for a sugar bowl and find a grotesque creature at the bottom flipping grains of sugar at them.

Crater-like antlion pits in the sugar bowl at Wayne's Word.

Eventually the larva attains its maximum size and undergoes metamorphosis during which it transforms into a winged adult. The entire length of time from egg to adult may take two or three years. According to Hutchins (Insects, 1966), this unusually long life cycle may be attributed to the uncertainty and irregular nature of its food supply. When it first hatches, the tiny larva specializes in very small insects, but as it grows larger, it constructs larger pits and catches larger prey. When it is full grown, the larva constructs a spherical cocoon of sand grains cemented together with silk. The cocoons of a common species of the southwestern United States are about the same size and shape as large rabbit droppings, and may be buried several centimeters deep in the sand. How the larva accomplishes this under the sand without getting sand grains inside the cocoon is rather remarkable.

Antlion cocoons resemble rabbit droppings covered with sand grains. They are often buried several centimeters deep in soft sand and are difficult to spot when you attempt to excavate them.

Close-up view of an antlion pupa inside its sand cocoon.

Antlion larvae collected in southern California in September formed their distinctive sand cocoons the following June and July, and winged adults began to emerge in August. During this time they were fed literally hundreds of ants, flies, silverfish and spiders, all collected at the headquarters at Wayne's Word. At times the staff wondered if they would ever stop eating and form their cocoons, especially since we were running out of food for them. Although we had a plentiful supply of Argentine ants, we found that this well-adapted little ant could sometimes escape from the sand pits, only to find food caches in the Wayne's Word kitchen cabinets, often returning with thousands of fellow food foragers.

The use of pitfall traps by primitive cultures dates back many thousands of years in Africa, and yet, antlion larvae have been using this method of capturing prey for millions of years with virtually little or no change. Like other fascinating creatures, their instinctive behavior is genetically programmed, each new generation knowing exactly how to perform seemingly impossible tasks with precision and artistic beauty. Antlions are particularly remarkable with ingenious pitfall traps and their clever method of outmaneuvering prey by creating miniature landslides. Their traps must be effective because antlions are abundant insects and they have been around for millions of years. During its larval life of a year or more, the antlion builds hundreds of pitfall traps and catches hundreds of insects. And yet, when the timing is right, it instinctively knows exactly how to construct a protective cocoon beneath the sand where it will gradually transform into a pupa and ultimately into a winged adult. The sand cocoon, with its glistening crystals of quartz, mica and feldspar, is truly a work of art.

The antlion is just one of many obscure creatures living in the southwestern United States. They are a marvelous little insect to observe in the wild, and they make a fascinating demonstration for a sand terrarium in the classroom. Although they live in a very competitive world, often within disturbed, urbanized areas, they are masters of survival under adverse conditions. If their little crater-like pitfall traps in the sand are obliterated by the wind, rain, animals, or popular two, three or four-wheel vehicles, they just rebuild it and calmly wait for their next prey. In fact, it is this ingenuity and perseverance that undoubtedly explains their survival through countless centuries.

The following information about antlions is summarized from Thomas Eisner's fascinating book For Love of Insects (2003). Ants of the large subfamily Formicinae have a very successful method of defence that involves the discharge of concentrated formic acid. They all possess a formic acid gland, a larger sac in the posterior part of their abdomen. With a concentration exceeding 50 percent, the formic acid is an effective irritant to their predators. When ants are pierced by the sharp jaws of the antlion, they are injected with salivary fluids. The soft insides of the ant are liquified by digestive enzymes and the ensuing "soup" is sucked up by the antlion through its hollow jaws. Studies conducted by Eisner and his colleagues indicate that antlions carefully avoid piercing the contents of the formic acid sac. In addition, the ants only discharge formic acid when they are biting their prey or predator. Ants are unable to bite the antlion's body because of its position beneath the sand. So even though antlions are repelled by formic acid, they avoid this irritant when catching and feeding on ants.

References:

  1. Evans, A.V. 2007. Field Guide to Insects and Spiders of North America. Sterling Publishing Co., Inc. New York, New York.

  2. Hogue, C.L. 1993. Insects of the Los Angeles Basin. Natural History Museum of Los Angeles County.

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