But invertebrates are perhaps most interesting when viewed not simply as duck food but as key players in a complex ecosystem. Each species has its respective role near the base of the food web that is the foundation for all life. Many duck hunters may have noticed what appear to be finely shredded leaves or crop stubble on the windward edge of flooded fields or woods. This is not the result of passive breakdown of the vegetation, but is evidence of the activity of a group of invertebrates called shredders. This group includes scuds and isopods like aquatic sowbugs. They are voracious feeders, mincing vegetable matter into infinitesimal pieces. Grazers such as snails also depend on the detritus that shredders feed on, scraping off the algae and microbes that grow on the surface of the debris.
Collectors, which include some midge and mayfly larvae, are next in the food chain, obtaining their nutrients and energy from more finely shredded vegetation. The smallest pieces of plant matter are consumed by filter feeders like fingernail clams. And as in all living ecosystems, predators prey upon the herbivores. Predaceous diving beetles and dragonfly and damselfly nymphs are all formidable predators in this ecosystem.
Although small in scale, these ecosystems can be easily upset by factors such as introduced species and pesticides. For example, pesticides have been shown to reduce the abundance and diversity of invertebrates in prairie wetlands. In addition, the introduction of minnows to previously fishless wetlands can wreak havoc on these miniature worlds. Small fish can consume a high proportion of the invertebrates in a wetland, and significantly reduce its value to breeding waterfowl. Consequently, while these ecosystems-in-miniature may often go unnoticed, we must take care to conserve them as key components of the larger ecosystems on which waterfowl depend.
FASCINATING SUBJECT Studying aquatic invertebrates is a great way to teach children about nature. Just scoop up a bucket of "duck soup" at your nearest wetland, pour some of its contents into a flat pan, and watch the kids' excitement as you introduce them to a whole new world.
Dr. Scott Yaich is director of conservation operations at DU national headquarters in Memphis.
Little Monsters In the tiny but complex wetland ecosystem of freshwater invertebrates, dragonfly nymphs are among the fiercest predators, like miniature versions of Tyrannosaurus rex. Although aerial as adults, immature dragonflies spend their lives underwater as nymphs. One of their most unique adaptations as a predator of other invertebrates and even small fish and tadpoles is their formidable set of mouthparts. Like many insects, they have hard, strong mandibles (jaws) that work side to side rather than up and down to tear their prey into smaller pieces. But what really sets them apart is their labium, or lower lip. The labium of dragonfly larvae is long, jointed, and has specialized structures that help it catch and hold prey. If you can imagine your arm stuck on your lower jaw and folded against your chest, you can visualize how the dragonfly's lower lip works and how it can suddenly reach out and grab prey.