Sunday, February 25, 2007

Rat tailed maggots

Who thought Nature could improve on a maggot? Well, she did. Rat tailed maggots are the aquatic larvae of syrphid flies who use a long posterior extension as a breathing apparatus. The insect larva is a mere 20 mm long, on average, but the "tail," a lot like a snorkel, can extend 15 cm. Small hydrophobic hairs are located at the end of the breathing tube which allow the insect to hang on to the surface of the water while it's breathing and prevent water from coming into the tube, allowing for proper gas exchange.

There are almost 100 species of syrphids worldwide. The harmless flies that resemble bees and wasps can be found hovering over flowers in every kind of habitat. Large numbers of their larval forms congregate in any accumulation of standing water. They're under every log I turn over, in every rainwater pool, in the swamp, in the bayou. The maggots are everywhere. They can live in clean water yet thrive in highly polluted water like septic tanks and sewerage lagoons. They feed on organic matter like decomposing leaves and animal feces and often appear in livestock lots where they can contaminate the water. In Cape Town, South Africa, the drinking water supply was briefly compromised with rat tailed maggots, whose presence caused several people to contract a gastrointestinal disorder called myiasis.

The skin of the rat tailed maggot is impermeable to insecticides and herbicides, which allows them to live in contaminated waters. They do not necessarily indicate poor water quality. All year they share rainwater pools with isopods, small crawfish, whirligig beetles and an amphipod commonly called a "scud," other invertebrates that are not as tolerant of pollution as the maggot. None of the invertebrates present, however, indicate pristine waters. Missouri's streams and rivers are regularly monitored by scores of volunteers who fan out across the state looking for the presence of invertebrate water quality indicators. High quality streams have caddis flies, stoneflies and water pennies in them. Unfortunately, the invertebrate indicators don't apply to swamps and sediment-laden backwater ditches, so I'm creating a list of critters to pass on to the other swampwater volunteers. The curious rat tailed maggot is included in the list.

I have some concerns about the park's water quality. Pesticide-filled ditches bisect the adjacent fields, run into the park, and distribute water laden with farm chemicals into the forest. My boss, Chief, graciously paid for an extensive water quality test that will detect 25 kinds of pesticides and mercury compounds that may be present in the park's waters; I've been summoned to Jefferson City to discuss the results (which hopefully won't be as bad as everyone suspects). Concerns were raised a few years ago when a state agency came to the park looking for salamanders in rainwater pools. No salamanders were found and various culprits were considered: paucity of adjacent upland habitat, pesticides in the soils and waters, maybe even mercury in the rainwater from Ohio Valley coal factories. While I complained about only finding high numbers of smallmouths last week, at least I found something other than the maggots.

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