miniSASS Newsletter July 2015

miniSASS Newsletter July 2015

nunu of the month: True fly

Phylum: Arthropoda
Class: Insecta
Order: Diptera

Some true flies can tolerate really filthy oxygen depleted water and use haemoglobin (red blood worm) or “snorkels” (rat tailed) to survive in these conditions.

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The true flies are a very large and very diverse group. The Diptera is one of the largest orders with most of their families having an aquatic based larval stage. Their common physical traits are their elongated worm-like bodies, eyes and pro-legs. Their bodies can also be soft and naked; others have structural adaptations like being able to stick to solid surfaces (mosquitoes and black flies).

The true flies eat dead organic matter, and some breathe through their skin, others aren’t able to get the oxygen and have special structures to get atmospheric oxygen in the air. Mosquitoes and rat tailed maggots actually have “snorkels” that are pushed through the surface film to get the oxygen. True flies are found dwelling at the bottom, adhered to different substrates or free swimming; they can swim with strong and fast wriggling motions while others crawl using suckers, spines or pro-legs to drag themselves around.

The true flies have been thought of in a bad way because they are able to survive really poor conditions and multiply rapidly in those conditions. True flies are also sometimes the hosts of deadly diseases like malaria. However, this group serve a great ecological function of decomposing dead matter and they use up the “filth” to clean the system. They score a low 2 in the miniSASS because they are not sensitive to pollution, except for the net winged midge that is found only in the clean waters of mountain streams.

True flies undergo complete metamorphosis, passing through four life stages. The eggs are deposited in shallow fast-running water, either attached to a substrate or scattered on the surface of the water. After hatching the larvae are released, this is also an aquatic phase. The pupa form and this phase does not last long, depending on the temperature of the water and the conditions. The pupa are in a case or a hardened skin, pupa also count in the miniSASS. The case splits and the young adult emerges.

Nunu Of The Month: The Other Mayflies

Phylum: Arthropoda

Class: Insecta

Order: Ephemeroptera

Mayfly larvae are the “cows” of freshwater streams and graze on algae. They swim by moving their abdomen up and down. The adult mayfly doesn’t eat at all and lives only for a few hours or days.

The other mayflies are a large group and they vary significantly. The common physical traits include three elongated tails, an elongated body, a large head, well developed mouth parts and true legs. Other mayflies have their gills on their abdomen, there is variation between the shape and the location of the gills.

The other mayflies are the cainflies which have a skirt like covering of the gills, the flat-headed mayfly that has a head broader than their body, the prongills that have gills with a unique shape and the stout crawlers that have very thick and stout arms. Others also include the brushlegged mayflies, pale burrowers and the water specs.

Other mayflies are the cows of the rivers as they graze on the algae and plant matter that grows on the rocks and on the floor in-stream. They breathe using the gills and move by swimming and crawling. The other mayflies are part of the diet of small fish, trout, frogs and birds. With a score of 11 on the miniSASS, other mayflies are moderately sensitive to pollution.

Mayflies undergo incomplete metamorphosis as they do not have a pupal stage. This involves passing through 3 life stages which are egg, nymph and adult. Each of these stages requires that the mayfly remain close to the water, the nymph is entirely aquatic whilst the adult is not aquatic but always stays close to the water.

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The article as it appears on The Water Wheel on the May/June 2014 volume 13 No 3 issue.

Get the whole publication online: www.wrc.org.za