Mayflies have ancestral traits that were probably present in the first flying insects, such as long tails and wings that do not fold flat over the abdomen. Their immature stages are aquatic fresh water forms (called “naiads” or “nymphs”), whose presence indicates a clean, unpolluted and highly oxygenated aquatic environment. They are unique among insect orders in having a fully winged terrestrial preadult stage, the subimago, which moults into a sexually mature adult, the imago.
Mayflies “hatch” (emerge as adults) from spring to autumn, not necessarily in May, in enormous numbers. Some hatches attract tourists. Fly fishermen make use of mayfly hatches by choosing artificial fishing flies that resemble them. One of the most famous English mayflies is Rhithrogena germanica, the fisherman’s “March brown mayfly”.[3]
Midges refer to several species of small, non-mosquito flies. To get more specific, most common midges include the family Chironomidae (midges) and Chaoboridae (phantom midges) in the order Diptera (referring to flies overall).
Now, to put that in terms that are more useful, midges are small, dainty flies (although some species can be bulkier) with one pair of long, narrow wings, and long, skinny legs. Males tend to have feathery antennae used to hear the high-pitched sounds emitted by the female’s wings.
While midges are usually found near naturally occurring lakes and ponds in small, non-nuisance levels, the abundance of nutrients within stormwater systems acts as a beacon to breeding midges and they can reproduce in vast quantities. That’s when they become an issue in communities.
Like other flies, chironomid midges have a four-stage life cycle (Figure 3). Females lay eggs on the surface of the water. Each gelatinous egg mass may contain over 1,000 eggs depending on the species. Eggs sink to the bottom where they hatch in several days to one week. After leaving the egg mass, larvae burrow into the mud or construct small tubes in which they live. Larvae enlarge their tubes as they grow. Suspended organic matter in the water and in the mud is used as food by the developing larvae. After they grow, the larvae take on a pink color and gradually turn red. Consequently, mature larvae (Figure 4) are commonly called “blood worms.” The red color results from an iron containing compound, haemoglobin, found in the midge’s blood. The haemoglobin allows the larvae to respire under low dissolved oxygen conditions in the bottom mud. The larval stage can take from 2 to 7 weeks depending on water temperature. Larvae transform into pupae while still in their tubes. After about three days, pupae actively swim to the surface, and adults emerge several hours later. Adults mate in swarms soon after emerging. More recent studies have shown that adult midges actually feed on nectar and other sugary materials. They live for only 3 to 5 days.
During the summer, the entire life cycle from egg to adult can be completed in 2 to 3 weeks. In the fall, larvae do not pupate. They suspend their development and pass through the winter months as mature larvae. Pupation and emergence of adults occur in the following spring in late March or early April. Several more generations of midges are produced throughout summer, resulting in mass emergences of adults that often aggregate on plant foliage near the water’s edge (Figure 5). In each generation, adults will typically emerge in large numbers for several weeks.
