Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
4/22/02
Contacts:
Donald Lewis, Entomology, (515) 294-1101, drlewis@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Yard and Garden Column for the Week Beginning April 26, 2002
Insects: The Water Garden's Unexpected Guests
By Ryan Holl
Plant Health and Protection Student
Iowa State University
and
Donald Lewis
Extension Entomologist
Iowa State University
Water gardens are increasing in popularity. Whether it's a whiskey barrel or a large, custom-built pond, a water feature delights the senses in ways grasses and shrubs cannot.
Water gardens can add many positive elements to the surroundings. Aquatic plants add texture and interest to the yard, while colorful fish can be the source of hours of quiet entertainment. Fountains and waterfalls allow owners to relax to the soothing sound of trickling water.
The more natural a pond is, the more native wildlife it will attract. Larger ponds can attract water-loving birds, amphibians, and small mammals. However, there are other things that ornamental ponds supply to their owners, totally free of charge, that are too often overlooked. Insects!
Insect Life
A body of water provides a brand new ecosystem that will attract many insects you might not normally see in your yard.
Dragonflies and damselflies, long slender insects with four large wings, are probably the most obvious insects to appear, and certainly some of the most pleasing. Their speed and agility as fliers can make them entertaining to watch as they dart around the water to capture their airborne insect prey, such as mosquitoes. These insects mate in the air, and it is not unusual to see two connected in flight. The female can later be seen flying down to the water to deposit her eggs at the water's surface.
Naiads, the immature form of dragonflies or damselflies, live in the water and feed on insects and other small animals. Their indescribable looks resemble something out of a horror movie and can be quite startling when come upon unexpectedly. Naiad skins can be found attached to plants above the waterline, where the immature insects crawl before molting and emerging as winged adults.
Water striders are a unique aquatic insect. They make use of surface tension to "walk" on water with two very long pairs of legs. Striders can be found "skating" on nearly every body of water in Iowa. They feed on small animals (mostly insects) that fall onto the water's surface or float up from below.
Whirligig beetles also scamper about on the water and eat insects at the water's surface. Groups of the small, glossy black beetles swarm restlessly until frightened, when they scatter. Their larvae (the immature form of the insect) feed on aquatic insects and mites.
The giant water bug, at up to two inches long and one inch wide, is one of the largest insects in Iowa. It has flattened rear legs for swimming and powerful front legs for grasping its prey. The giant water bug usually targets insects, tadpoles, fish and amphibians as food. However, it has been known to clasp onto the toes of passing humans, earning it the nickname "toe-biter."
These are just a few of the interesting animals that may inhabit a water garden. Others offer equally entertaining appearances and behaviors. Unfortunately, very few great things come without costs. There are a few negative impacts that insects can make on your water garden.
Naiads, several of the aquatic beetles and the giant water bug can feed on aquatic animals such as very small fish. This is of little concern to most pond owners however, since these animals rarely, if ever, attack fish as large as "feeder" goldfish frequently used to stock ornamental ponds. However, if the water garden is large enough for fish to reproduce, naiads will certainly pose a threat to very young offspring.
What about mosquitoes?
The mosquito is the biggest concern when dealing with bodies of water in the yard. Mosquitoes lay their eggs in stagnant water, where the larvae, or "wrigglers," develop. Wrigglers feed on organic matter in the water until they are ready to pupate and change into the flying, blood-sucking nuisance that everyone knows as the mosquito.
Fortunately, there are measures you can take to reduce mosquito populations in your water garden. Keep the water in motion with a fountain or filtration system to keep mosquitoes from reproducing - they prefer to lay their eggs in stagnant water. Pond design and layout, including steep banks with little vegetation along the water's edge, can also deter mosquitoes from reproducing in the water.
The mosquito also faces many natural perils in the water garden environment. Amphibians, insects and fish consume mosquito larvae as they float near the surface. Adult mosquitoes face further torment when adult dragonflies and birds attack them from the air. All of these factors work together to reduce mosquito problems.
A water feature offers many different and interesting benefits to you and your yard. The next time you find yourself enjoying one, try to appreciate the little details that nature throws your way. Pleasure often comes from unexpected places!
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