Chironomus annularius

C. annularius has three defining characteristics in terms of physical structural. The first is the Johnston's Organ, a sensory organ embedded in its antennae.[1] This sensory organ is used to detect other individuals of the same species and possible mates. The range of detection is no more than a centimeter; this small range requires the species to try mating on even the slightest hint that there's a female nearby.[2]

Green/Left = Higher Physical Fitness Blue/Right = Higher Reproductive Fitness

Additionally, the species are characterized by a difference in size between large and small males. The larger males have higher longevity and can fly for more extended periods of time. This allows larger individuals to search for food and resources and succeed more in physical fitness. The smaller males are at a disadvantage physically, but they can more easily latch onto females in the air to mate. Thus, the reproductive fitness of smaller individuals is also high. Medium-sized males don't experience any of this benefit, and thus are not as populous.[1]

Lastly, there is a difference in wing spans and frequency of sound between males and females. This is due to the inverse relationship between the sound that the wing produces and wing length. For example, C. annularius males have shorter wingspans, which causes them to produce higher frequency sounds (434±27.8 Hz). On the other hand, females have longer wingspans, which causes them to produce lower frequency sounds (240±17.2 Hz). This allows males to differentiate between other males and possible mates.[1][3]

Great Lakes

This species exists in every climate except the harsh heat of some deserts.[4] There have been notable sightings of their swarming behavior in the Great Lakes, the swamps of Florida, Lake Ijssel of Netherlands, and multiple lakes and rivers across England. The males are known for their swarming behavior for both physical fitness and reproductive fitness reasons.[5][3] This swarming causes individuals to arrange themselves more densely in certain hotspots, increasing the population density around these select areas and decreasing the population density elsewhere.[3][6]

The related species Chironomus antrhacinus

The first documented accounts of the Chironomidae family were in the late 19th or early 20th century in England.[9] Entomologists at first had trouble differentiating the difference between subfamilies and genera of the Chironomidae, but had a breakthrough regarding the recognition of difference in their pupal stage.[10] The genus name Chironomus was decided, which was derived from the Ancient Greek word cheironomos, meaning to gesture with your hand.[11] This followed the spirit of the family name Chironomidae, which in Ancient Greek means a pantomimist or one who entertains or dances with exaggerated hand movements.[12] These meanings of names most likely alluded to the swarming behavior and movement of the midges belonging to the Chironomidae family.[5] Lastly, the species name, annularius, is derived from the Latin language, with the meaning 1 year old or annual.[13] This naming is contradictory to the life span of the adult non-biting midges (3 days to a few weeks) but may be related to the seasonable noticeability of the C. annularius, particularly in spring and fall.[10]

Due to the broad distribution of the Chironomus genus across the world, it has been given a plethora of nicknames.[10] In North America, they are called chizzywinks or blind mosquitos near Florida, and in the Great Lakes region, they are referred to as bay flies or lake flies.[14] Further north in Canada, the Chironomus are called muckle heads or muffle heads.[15][16] Across the Atlantic in England, the Chironomus are referred to as non-biting midges or common midges.[17] The diversity of name for such a genus of insects suggest that it exists almost worldwide.[10]

Examples of Insect Predation (Not C. Annularius)

Swarming behavior or "aerial aggregations" is a common social behavior for the fly species.[5][3] There are costs and benefits to grouping with other members of your species. Individuals experience decreased rates of predation. This is due to an overall decline by predators on a swarm as well as the dilution of predator attacks per individual. Feeding has also been proven to be more efficient in larger populations. This may be due to group communication and direction to food and resources. Lastly, swarming of males increases the attraction of females, because the sound of the flight tone is amplified when they band together.[1] This may not necessarily increase reproductive success of all individuals, but rather individuals that are able to detect and mate with females first experience the benefit of increased reproductive fitness.[2]

Frequency (High vs. Low)

The C. annularius species has specific flight tone frequencies. Males have an average frequency of 434 Hz and females have an average frequency of 240 Hz.[3] Different genera of the Chironomus have different frequencies, thus the discernment of tonal frequencies is particularly important in swarming and for mating.[1]

C. annularius, like most Diptera insects, differ in their diet through their life cycle. Larvae have mandibles and varying internal teeth. These larvae feed on fine particulate organic material floating at the bottom of the body of water they were born in. This diet of decaying material continues with a brief intermission during the pupal phase, until adulthood. Once the species emerge from their cocoons and out of the water, their diets change dramatically. The most noticeable change is that the individuals no longer feed on submerged organic particles. They transition to feeding on surface algae, secretions of aphids, and other plant material. Although the species resembles its close relative the mosquito, it is a non-biting midge and does not consume blood.[10]