Doc Leonard’s Lecture Notes on the Megaloptera and Neuroptera
Introduction
Megaloptera
NeuropteraWe now take leave of those insects characterized by gradual or incomplete metamorphosis. So far as aquatic insects are concerned, the first Order displaying complete metamorphosis is the Order Megaloptera, comprising in terms of common names, the alderflies, fishflies, and dobsonflies. Alderflies are placed in the Family Sialidae, while the dobsonflies and fishflies both belong the Family Corydalidae. Students of insect systematics and phylogeny are not in agreement as to whether these families constitute an Order of their own, the Megaloptera, or whether they should simply be placed in the larger Order, Neuroptera, grouped as a sub—family with either the name Megaloptera or Sialiodea. Chandler, Pennak, and Evans elect to treat them as a full order and they will be treated as such here. It would seem that justification for ordinal status is in the trait of having aquatic immature stages unlike the other neuropteran families with the exception of the Sisyridae (spongillaflies).
Despite the fact that these insects are quite noticeable and in the case of dobsonflies and fishflies, quite large and attention—attracting, they still have drawn very little notice from professional entomologists. In Aquatic Insects of California, the chapter on this Order was prepared by H. P. Chandler of the California Department of Fish and Game. It was hoped that we would contribute much to our knowledge of these interesting insects in future publications; however, even before the manuscript for Aquatic Insects of California had cleared the printer, Chandler had died. So it is that one must go back to 1903 (K. C. Davis) or 1910 (van der Weele) to find much in the published literature on the ecology of this order. H. H. Ross, who did much to further our knowledge of aquatic insects in general had one useful paper on the genus Sialis, but it is almost entirely taxonomic in nature. E. D. Evans in An Introduction to Aquatic Entomology has summarized much of the literature and his own studies to produce the best modern work on this order.
In the larval stage, alderflies differ from dobsonflies and fishflies chiefly in having a single terminal filament and seven pairs of lateral filaments on the abdomen, instead of a pair of hooked anal proleg and eight pairs of lateral abdominal filaments. From the standpoint of size when the larvae are mature, there is no difficulty since sialid larvae are always much smaller than the others.
Alderfly adults, with few exceptions, are fairly large, black, broad insects, rather sluggish in their movements. They seem to fly laboriously and spend much of their time clambering, rather awkwardly, over bushes or other resting places. The adults are diurnal and in general are most active during the middle of the day. They mate on the wing, although mating is likely to be completed while in some normal resting place near or over water. The females deposit eggs in rows which form large masses, and these masses are usually situated on objects which hang over the water-tree branches, bridges, or other appropriate surfaces. The larvae fall into the water as soon as they hatch but are quite small and extremely hairy and may need the rough water of a riffle just to break the surface tension.
Larvae are predaceous and usually are found under or between gravel in the stream bed or lake bottom where they search for and feed upon midge larvae, small Mayfly nymphs and other animal life. When full grown, they crawl out of the water and dig into the moist soil where they form an earthen cell to pupate. The adult which emerges is short—lived. The mouthparts are soft and do not appear to be fitted for feeding.
The Family Corydalidae, embracing the genera Chauliodes, Nigronia, and Corydalus, contains the showier members of the order (in the West, there are additional genera, but the three mentioned are the only ones found in this part of North America). Some of the members of this family, as adults, have a wingspread in excess of 6 inches. The adults of the common dobsonfly, Corydalus cornutus, are spectacular, and the males which have tremendously enlarged mandibles spread terror among innocent cottagers seeing them for the first time. It is supposed that these enormous mandibles are used in clasping the female during mating but strangely enough, this has not been observed. The wings of both Corydalus and Chauliodes are essentially leathery and nondescript gray in color. The genus Nigronia is the commonest along trout streams. Adults of Nigronia can be recognized on the wing as far as one can see them because their wings are a striking, deep brownish—black with conspicuous white bands across them. They flutter weakly up and down the streams, always seeming about to come to grief, but always just managing to elude this, that, or the other danger. Their seemingly weak, haphazard flight is probably a highly-evolved development with survival value. In the literature, Nigronia is described as a sluggish water species. This does not seem to hold in Michigan as here they are associated with the swiftest riffles.
Larvae of the Corydalidae are known to the angler as hellgrammites. In each of the three common genera, these larvae are large, forbidding looking, generally black in color, and with extremely business—like jaws capable of inflicting a very real pinch upon the fingers of the handler. Hellgrammites are beloved of bass fishermen not only because they are indeed an effective bait, but because they are so tough of body and so tenacious of life that they “last” on the hook for a long, long time and can be kept for long periods in damp moss in a bait can.
Hellgrammites seem to have a preference for the undersides of large stones and boulders in water of considerable depth and current velocity. They have long, lateral filaments on 8 of the abdominal segments as indicated earlier. In Corydalus there is a tuft of filamentous gills at the base of the lateral projections, and in Nigronia, the last pair of abdominal spiracles is situated at the end of a pair of projections for surface breathing. As is the case in Sialis, the corydalids deposit their eggs on surfaces overhanging the water. The egg mass of Corydalus cornutus quite accurately resembles a large bird dropping and often may be found in great numbers on leaves and rocks above the water. Larvae are strongly predaceous and will resort to cannibalism even in the pupal stage.
It is thought that Sialis probably has a one-year life cycle. In the case of the corydalids, the larval period is not certainly known, but there is good reason to believe it may last at least as long as 3 years. This view is based on the apparent size classes of larvae which may be collected as a given stop at one time. Like the larvae of Sialis, those of Nigronia (and presumably other members of the family) leave the water and crawl some distance along the surface of the ground seeking a spot to pupate. The pupal period may be about 2 weeks in duration. Most of the life history details are quite sketchy, but one interesting observation was made by R. Van Dusen of the Kellogg Sanctuary. He observed a hellgrammite traveling across pastured land away from a stream quite obviously seeking a place to pupate. When it finally seemed to find a suitable spot, it happened to be under a pile of cow manure some days old. It is possible to surmise that it was seeking the “hothouse effect” which would be produced by the heat of the composting manure. It would be of interest to further test this observation and see if pupation really is dependent on an added source of heat for completion of metamorphosis. Chandler mentions a Serra species of temporary streams which, when kept in dry soil, did not become dormant but fed on termites and other live insects. This species laid its eggs on rocks in the stream bed and also pupated there.
As a final thought on the Megaloptera: why are the corydalid larvae referred to as hellgrammites? The only answer that seems to be given is that they look like hellgrammites.(back to top)By placing the alderflies, dobsonflies, and fishflies in the order Megaloptera, we are left with only a single North American family in the order Neuroptera. This is the family Sisyridae comprising the so-called spongillaflies. The aquatic family Oscylidae occurs elsewhere in the world. Marcus Old, a former University of Michigan student, published some observations on Sisyridae in 1932, which still constitute much of our knowledge of this group. H. P. Brown described the life cycle of Climacia areolaris in 1952 and much of his information and drawings are still used in textbooks. Parfin and Gurney, in 1956, summarized much of the world literature. Apart from these, little has been published on the family.
Like the Megaloptera, eggs are laid above the water. Upon hatching, the larvae enter the water and seek out members of the freshwater sponge family Spongillidae which they parasitize. They have long piercing mouthparts which enable them to draw material directly from living cells of the sponge. Larvae undergo 3 instars and a population may have several generations in a single year. Also, like the Megaloptera, mature larvae leave the water often traveling great distances to find a suitable spot for pupation. Members of this family do not construct earthen chambers but pupate in the open where they create ornate canopies of fine-mesh silk. If the canopy is perfectly made, it will protect the pupa from a specific parasite wasp which seems to be everywhere one finds spongillaflies.
In this part of the country we have 2 genera, Climacia and Sisyra, each with a single species. For Climacia, the larvae are most common in sponge colonies in streams and wave-swept margins of lakes; adults are small, net-veined, brownish appearing insects reminiscent of a small brown lacewing or Hemerobiidae. The larvae of Sisyra occur in sponges in small ponds or still waters; the adults resemble Climacia but have clear instead of brownish wings.
Though not particularly common, freshwater sponges and spongillaflies do occur with some regularity in Michigan streams and lakes, and it is not only the spongillaflies which have utilized this unique food source. One may also find species of the caddisfly genus Ceraclea (Leptoceridae) and genera of chironomid midge larvae, in particular Xenochironomus xenolabis.
These insects are very interesting from a standpoint of the general student of biology or entomology. They appear to have little practical significance in fisheries or pollution as their life cycles, abundance, and distribution seem quite controlled by the distribution of freshwater sponges. (back to top)page converted to html: 12 March 2001 (EB)