Insect external structure
Insect internal structure
Development of insects
Relationships of insects
Insect identification > Neuroptera
The insects placed in this group, though quite similar in structure, differ markedly in appearance in many cases. They vary much in size, ranging from less than a quarter of an inch to several inches in length, and their wings may be small or large.
The mouth-parts are for chewing or biting, and most of the group feed upon insects and other small animals. The wings are four in number, well supplied with both longitudinal and (with a few exceptions) cross veins.
The larvae in general are active, moving about in search of their prey. A few, though, live in the egg sacs of spiders, feeding on the young spiders, and in one or two cases fresh-water sponges appear to be their food. There is a quiet pupa stage.
The group may be characterized as: Insects which when adult have two pairs of wings usually large as compared with the body and with numerous longitudinal and (in most eases) cross veins. Mouth-parts for chewing. Metamorphosis complete.
So far as is known, none of the Neuroptera are injurious insects and some at least are decidedly beneficial. About half a dozen families are usually recognized and some of these are here considered, either because of their economic importance or because they are large and common enough frequently to attract attention.
In the family Sialidae belongs the largest member of the order found in the United States. This is commonly called the dobson fly or hellgrammite (Corydalis cornuta L.), which is quite common throughout the country except in arid regions.
The mandibles of the male are nearly an inch long, slender and somewhat curved; those of the female are short. The distance from tip to tip of the wings, when these are extended, may be over five inches, and the size of the insect and the long jaws of the male have led to the mistaken belief that this really harmless animal is dangerous.
The eggs are laid in large masses on objects which hang over the water, into which the larvae enter on hatching, making their way under stones where they feed for nearly 3 years on the nymphs of May flies and other insects. Here they are searched for by fishermen to use as bait.
When full-grown, the larva makes a cell under some stone close to the stream and pupates for about a month, after which the adult escapes.
Smaller species, with white, belong some with gray or black wings or black wings spotted here. They are often quite common around streams and ponds during the summer months and are frequently called "fish flies."
The members of the family Chrysopidae are of great economic importance as the larvae feed freely on injurious insects, particularly aphids, and are so voracious that they are often called aphis lions.
The adults are rather small, slender-bodied insects, averaging less than an inch long, with long antennae and large, finely veined green wings, which when not in use are carried sloping over the body.
These adults are sometimes called "goldeneyes" because of their shining, golden-yellow eyes, but perhaps more frequently "lacewings," from the delicacy and beauty of these structures.
The lacewings are found practically everywhere in this country and are usually quite abundant. They lay their eggs on the stems, branches and leaves of plants, first constructing a slender but quite stiff stalk of silk about half an inch long, to the end of which the egg itself is attached. These eggs are usually placed in groups and it is believed that, were the eggs not raised on stalks out of reach, the first larva to hatch would at once proceed to eat the eggs as its first meal.
These larvae are rather short, somewhat oval in outline, and have long mandibles with which they grasp their prey. The lower side of each mandible is grooved and the maxilla of the same side is so modified as to fit into this groove and convert it into a tube. An insect attacked by an aphis lion is seized by the tips of the jaws and its blood is drawn through the tubes into the body of its captor.
Aphis lions are often found in colonies of aphids which have by their feeding caused leaves to curl, and, with an abundant food supply thus provided, the insect is both protected by the leaf and insured of the food it needs for its development.
When full-grown, the aphis lion forms around its body a white, shining, spherical silken cocoon in which it pupates. When this process is complete, the adult cuts out a circular piece of the cocoon, forming a hole through which it escapes.
The importance of lacewings as friends of man is such that they should be protected and not destroyed under the impression that being among known pests they must also be for that reason injurious.
In the Western states are a few insects belonging to the Neuroptera, and family Raphidiidae. They are small, less than an inch in length, but with an unusually long prothorax. The larvae feed on other insects and, among others, on codling moth larvx.
They occur chiefly under loose bark in this stage and, while not so abundant as could be desired, do good work by attacking many injurious species. They have been introduced in Australia in the hope that they may become effective enemies of the codling moth there.
Another family, the Mantispidae, though few in numbers, has its members quite widely distributed. The mantispas, as they are called, like the raphidians, have a greatly elongated prothorax and their forelegs are also long and adapted to grasping their prey. The adults are larger than the raphidians, being about an inch in length and with long wings. Though feeding on other insects, most of which are likely to be injurious, the mantispas are not numerous enough to be of any great importance.
The insects belonging to the family Myrmeleonidae are generally spoken of as the ant lions, though the name "doodlebug" is sometimes applied to their larvae. They are widely distributed over the United States, particularly in sandy places, but are most abundant in the South.
Many kinds of the adults superficially greatly resemble the "damsel fly" section of the dragonflies (Odonata), their long, slender bodies, large, gauzy wings and their general size causing the resemblance. Their antennae, however, instead of being very small and not noticeable, are of fair size and knobbed at the tip, which provides an easy way by which to distinguish the two groups. Other characters and their life history also prove that the resemblance is only superficial.
The larvae of the ant lions greatly resemble those of the lacewings in general form and in the possession of long jaws grooved for sucking the blood of their victims. They excavate little conical pits in soft, dry, preferably sandy ground, an inch or two across and as deep as possible for the. sandy sides to hold. At the bottom of the pit thus dug, the young ant lion buries itself except for its head and waits for an unwary insect to fall in. Sliding down the slope of loose earth, the victim literally falls into the jaws of the waiting enemy and is killed and devoured.
It has been stated that sometimes the insect on its way down the side of the pit is able to check itself and start to climb out, and that then the ant lion shovels a load of sand on to the top of its flat head, with its leg, and snaps the sand up the side of the pit, where, falling, it sweeps the prey down to the bottom within reach of the ant lion!
The process of excavating the pit is also one of extreme interest. The insect first traces out a circle of the desired size, loading its head with sand from inside the circle and snapping it out and, on completing the circle, repeats the process but in the reverse direction, and this is continued until the pit has been completed. In doing this the larva always moves backward.
After becoming full-grown, the ant lion larva forms a spherical cocoon of sand and silk in the ground, within which it transforms to the adult. The ant lions, though feeding on other insects, are of little, if any, economic importance, as the forms they are most liable to capture are not often serious pests. Their habits and manner of life, however, are so interesting that much attention has been given to them and what has been published about them forms one of the most interesting chapters of entomology.
The Neuroptera, though widely distributed over the world, do not constitute a large group. Only about two hundred kinds are known in this country and rather less than four thousand kinds in all have thus far been discovered. Fossil specimens of several of the families have been found.