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Cofrin Center for Biodiversity

Metamorphosis is Tough!

And you thought growing up was tough…try metamorphosis. This unfortunate insect is probably a Spongillafly. It should have long lacy wings (see link for comparison), however, something must have happened as it emerged from its pupae.

When botanist Gary Fewless found this tiny creature, he had no idea just how unique it was.  He found a spongillafly, an insect that is seldom collected as adults. And he found a living individual whose abdomen and wings were highly deformed. 

At least we think it is a spongillafly. We are not completely sure of course, since we are making an identification from a photograph of a badly deformed specimen, but that is entomologist Mike Draney’s best guess, based on the size of the eyes and the pigmentation of the wings. And what exactly is a spongillafly? They are insects in the Order Nueroptera, which also include the more familiar lacewings and ant lions (aka doodlebugs if you’re from the South).  Most Neuropterans are predators. However, spongillaflies are unique, because they are parasites that spend their larval stage underwater feeding on freshwater sponges.  Only 6 species are found in the spongillafly family (Sisyridae) and only 3 of these, Climacia aerolaris, and Sisyra fuscata, and Sisyra vicaria are found in the Great Lakes region.

The adults look similar to brown lacewings. They spend their time flying, feeding and scavenging on other invertebrates, mating and laying eggs on vegetation overhanging streams and lakes usually at dusk or after dark, which is one reason they are so seldom collected.  When the larvae hatch, they fall into the water and float around until the find a sponge. (Wait a minute…there are sponges in Wisconsin?  Well—yes, but we’ll tackle that topic in a later blog. ) The spongillafly larvae use their piercing mouth parts to suck body fluids from the sponge tissues. They don’t kill the sponge and will stay with the same sponge until they are ready to pupate. It is likely our specimen spent its underwater time feeding on its sponge and generally enjoying life.  When it was ready to metamorphose it climbed out of the water, found a site it liked under a rock or tree bark and then spun a silken cocoon around itself for protection. It remained in the cocoon all winter as a hibernating larva, waiting until the warm spring weather to even begin to pupate.  And that is where something went terribly wrong. 

What goes on in the pupa? From our perspective, pupation might seem like a pleasant rest in a bed of silk, this is hardly the case.  Beneath its silken wrap, dropping levels of juvenile hormones trigger a cascade of changes in the developing insect. First, chemical signals are released that signal the epidermal cells to release enzymes that digest the larvae’s cuticle (skin). The cuticle is broken down into and reused to make new parts. Basically the larva is killing its own skin cells.

At the same time special clusters of cells in the body called imaginal discs become active and elongate, using the digested epidermis to  build wings, eyes, antenna, and reproductive parts, as well as the new exoskeleton of the adult insect.  These discs are aligned in pairs and their development is genetically controlled. Any mutation in these genes can result in malformations in the adult, so that a leg might grow where a wing should be.  In fact, it was the study of mutations like these in fruit flies that greatly increased our understanding of how the process and genetic control of early developments occurs.   If anything goes wrong during this period of genetic communication and rapid development the adult will not form properly.

Our insect has all its parts in the right places, so a genetic mutation is unlikely. It is more likely that the pupa was damaged from the outside as it was developing. If the pupa is crushed or bent during this period of radical re-arrangement, the underlying developing adult structures can also be damaged. The developing pupa does not have much capability to repair structures after they have formed.

Damage can also occur after the adult emerges, but before its exoskeleton dries and hardens. The newly emerged insect is soft and its wings are shortened and curled. It must pump fluid from its abdomen into the veins of the wings to enlarge and elongate them.  (See this photo of a newly emerged brown lacewing.  It has nearly finished uncurling its wings.) If the insect falls or is crushed while it is still soft, wings or legs can harden in bent positions. If the abdomen is damaged, internal injuries can result, and the insect will usually die.

Parasites can also cause improper development. Gregarine parasites are protozoa that live in the guts of many different insects including Nueroptera.  The insects are infected by spores that fall onto the eggs as they are being laid.  The spores are eaten by the insect larva and reproduce asexually inside the gut, absorbing nutrients through micropores in their wormlike bodies. During pupation the parasites switch to sexual reproduction, forming spores that are released through the pupal case and dust the body surface adults as they crawl out of the cocoon. They pass the spores onto their offspring when the spores fall onto the eggs as they are laid.  Heavy gregarine infections are known to result in wing deformations in developing butterflies because the butterflies are too weak to hold themselves up or to inflate their wings.

We are not quite sure what went wrong with this individual.   Regardless of what happened to this insect it is unlikely it survived very long after the photo was taken.