Some ecological threats are subtle, hardly drawing any notice except in scientific circles.
Then there is the northern snakehead, an exotic invader so obviously evil it is difficult not to recoil in horror. At least that is what Missouri officials hope.
The Northern snakehead (Channa argus) is native to northern China and Korea. Individuals arrived in North America as aquarium fish, but escaped or were released into the wild.
The first known wild populations were discovered in Maryland lakes in 2002.
Some live snakeheads were sold by a supermarket in Los Angeles in 2002 and 2003. The fish turned up in a tributary of the Potomac River in Maryland in 2004.
Since then they have been found in places as far apart as Pennsylvania, Wisconsin and Florida.
On April 14 this year, a farmer discovered a northern snakehead wallowing on the banks of a drainage ditch in Lee County, Ark.
He reported the sighting to the Arkansas Game and Fish Commission, which confirmed that a breeding population of the fish existed in nearby Piney Creek.
Arkansas officials quickly applied rotenone, a chemical that suffocates fish, and recovered about 100 dead snakeheads and half as many live specimens measuring up to 20 inches.
However, they said it was likely that floodwaters already had allowed the fish to spread to other streams in the White River Basin.
The headwaters of the White River extend into southwestern Missouri and northwestern Arkansas.
Arkansas officials said that once the northern snakehead reaches the White River it will have free access to the Arkansas, St. Francis and Mississippi river systems as well.
The U.S. Fish and Wildlife Service added snakeheads to its list of banned species in 2002.
A fish farm in Monroe, Ark., raised northern snakeheads in 2000.
Arkansas officials speculate that some of those fish might have escaped destruction.
Escapes are particularly possible for snakeheads, which can breath air and may travel some distance overland as long as they remain moist.
The northern snakehead's habitat needs and food habits are similar to those of the largemouth bass, leading fisheries biologists to worry about how the invader could affect native populations of fish and other animals.
The northern snakehead can reach 5 feet in length and weigh up to 13 pounds and is a prolific breeder.
The northern snakehead is similar in size and appearance to the bowfin (Amia calva) a fish native to southeastern Missouri and the Mississippi River.
The most certain way to tell a snakehead from a bowfin is by the length of the anal fin, which is on the belly just in front of the tail.
Snakeheads' anal fins are long, like the fins that run down their backs.
Bowfins' anal fins are much shorter in their attachment to the belly.
Snakeheads also have diamond-shaped markings on their flanks, compared to the uniform olive green of bowfins.
Bowfins have a large, dark spot near the top of the tail where it meets the body.
Anglers who catch suspicious fish and anyone who sees a fish resembling the northern snakehead are asked to contact the nearest Conservation Department office immediately.
Anglers should not release suspected snakeheads, but kill and keep them until a fisheries biologist can determine their identity.
The snakehead is just one of dozens of non-native aquatic pests that could cause ecological damage in Missouri. Others include the zebra mussel, the rusty crayfish, several species of Asian carp, didymo (an invasive algae) and numerous aquatic plants.
One of the best things anglers can do to prevent snakeheads and other exotic animals from entering Missouri is to dispose of live bait properly.
Unused bait should be placed in trash bags and deposited in trash receptacles away from water. Never release unused bait -- whether fish, worms, crayfish or anything else -- into lakes or streams.
The northern snakehead is a prohibited species under the Wildlife Code of Missouri, making possession of live snakeheads illegal.
For more information about the northern snakehead, visit invasivespeciesinfo.gov/aquatics/snakehead.shtml.