The little blue damselflies were flying all around me as I walked on the trail next to Frog Creek. The heavy rains this past spring must have encouraged their hatching. Their feeble wing beats were just strong enough to keep them a few feet in front of me.
Damselflies are insects that are in the same order as dragonflies; they have similar looks and life cycles, but there are differences. The more delicate damselflies hold their wings upward while at rest, where as dragonflies rest with their wings spread at right angles to their body. The damselflies are also smaller and they are weaker fliers. Because they are poor fliers they are always found near the water where they hatch. There are forty-two recorded species of damselflies in Iowa and eight of these are imperiled. Two of the more common groups are the black-winged damselflies and the bluet damselflies.
Scientists are paying more attention to these insects now because they are considered one to the bellwether species that are indicators of water quality. The reason for this is the larvae must have clean water for their growth and development.
Damselflies mate while flying. Shortly after mating, the female drills a hole in the stem of a water plant with a special organ at the end of her abdomen and lays her eggs inside the hole.
After the eggs hatch, the baby insects live in the water and are called nymphs. The nymphs look a little like the adults but they don’t have wings. They shed their skin several times as they grow, slowly taking on the form of the mature adults. Scientists call this growth process ‘incomplete metamorphosis".
During their life in the water the nymphs obtain oxygen from three gills on their tail and feed on any animal or insect that is smaller than they are. Their favorite food is daphnia or water fleas, but they will also eat small worms and baby fish. Sometimes nymphs can be seen crawling on plants in search of prey, but most of the time they hide in the mud and wait for the food to come to them.
About the middle of June they will crawl out of the water onto a rock or log and shed their skin for the final time. Their exoskeleton splits lengthwise along their back and adult damselflies emerge. They need to wait several minutes until their wings dry and become hard before they are able to fly. The adults live for several weeks during the summer, feeding on small insects and breeding several times. The eggs of damselflies can survive the winter in the plant stems and newly hatched nymphs hibernate in the muddy bottom of the stream during the winter. In the spring the cycle begins again.
Last spring the Raccoon River Watershed Association gave a grant to a Drake University student to study the nymphs and other insect larva in the North Raccoon River near Jefferson, Iowa. He wants to determine if the oil spill that occurred there in the fall of 2012 had any serious impact on these important insects that live in the river. Also, Iowa’s Department of Natural Resources is now using damselflies for part of the long range wildlife plan and water quality study. These insects are important to the food chain in a stream and they eat harmful insects that bother humans. But what is more important is that large numbers of damselflies indicate good water quality. I was pleased that the water quality in Frog Creek was suitable habitat for these interesting insects.