The stability of any ecosystem depends on having a multitude of species playing different roles in that ecosystem. Some are producers, some are decomposers, some are predators, and no one gets out of hand. The predators don't take over because there are bigger predators, disease organisms, and competitors for food and other limiting factors.
Invasive species are the newcomer species that upset the fine balance, altering ecosystems and even causing extinctions. For example, entire food chains have collapsed in the Great Lakes due to the invasion and overgrowth of the zebra mussel. The zebra mussel eats all available algae, and other species starve.
Invasive species arrive in many ways - sometimes by expanding their range but usually because they have been carried from one place to another by humans. Our species of the day, the Japanese beetle (Popilla japonica) (picture), was accidentally brought into the United States from Japan as grubs in soil of ornamental plants. The new species was detected in New Jersey in 1917 and quickly traced to a plant nursery in the area.
Because invasive species are new to an ecosystem, they are neighbors with other species to which they have not evolved. That means their neighbors have not had a chance to adapt to eating the invasive species, or competing with it or infecting it. That's how you end up with entire mountains covered in kudzu. Or the entire eastern United States covered in Japanese beetles (range map), despite massive federal, state and private efforts to destroy this aggressive farm pest.
But even invasive species are fascinating. Japanese beetles are beautiful, metallic beetles. Also, they might just be the only insect capable of growing one body part at a time, according to Dr. Hans-Willi Honegger, an entomologist who also works on the farm. Dr. H thinks they might be able to grow their jaws, which would make sense since they are such voracious feeders. Japanese beetles' life cycles are also very interesting. They emerge in late spring, feed like crazy on leaves of their favorite plants, mate and lay their eggs in the soil. Most of the adults die off by late August, but the larvae are just starting to get busy. They burrow in the upper layers of soil throughout the fall, eating roots and organic matter in the soil. When the temperatures start to drop, the beetles burrow deeper and deeper to stay warm only to come back up when the spring thaw comes again.
On the farm, the beetles are just starting to emerge. According to the farm owner, the beetles have gotten a little worse over the past few years as their range has expanded. Now that they are here, they are probably already laying eggs here for next year, and their numbers may increase. Once beetles establish themselves, they are really impossible to get rid of, but several strategies can help. A soil drought during early larval stages can kill many larvae; parasitic wasps, worms or bacteria can be released into the area to help kill beetles; traps do attract beetles, but they don't seem to help the overall problem; and insecticides are of course used on non-organic farms. A surefire way to control Japanese beetles would be to simply wait around long enough for evolution to take its course. All those Japanese beetles are a great food source for any animal that could evolve to eat them. Given the rate of evolution, we might only have to wait about 20,000 years for Japanese beetles to become a part of our balanced ecosystem.