I have the answer to this question. They care called swarms, and
they're part of the mating ritual for a type of insect who's Genus is
Chironomid. Chironomid covers the larve, which are more commonly
called bloodworms, and Midges and Gnats, 2 common names for insects.
There are over 200 Chironomid species.
Midges and gnats are common names for a large number of small,
non-biting flies. Many species look like mosquitoes and may form
annoying swarms or clouds in the air but they do not bite. The
immature stages develop in water in pools, containers, ponds, clogged
rain gutters, or in some cases, wet soil or seepage areas. Most feed
on living or decaying plant matter and are an important part of
aquatic food chains. Many species can survive in very stagnant or
Large mating swarms of adults often appear about dusk and may occur
for several days, especially after a prolonged wet period. Many gnats
are attracted to light and may be a nuisance, landing on people or
entering homes or businesses. These tiny flies do not feed. They only
live long enough to mate, lay eggs, and die. Eggs are laid in masses
in the water or on aquatic vegetation. The life cycle usually takes
about 4 to 5 weeks. There may be several generations during the summer
but these insects usually disappear with the onset of dry weather.
Fortunately, problems are usually temporary and intermittent.
In the late evening (and to lesser extent at sunrise), large masses of
male Chironomids, some with millions of individuals, form in relation
conspicuous element of the landscape. The Chironomus swarms seem to
locate themselves above such landmarks as the summer road, the beach
or even a conspicuous tree. These swarms remain a relatively constant
distance from the swarm marker, adjusting height and position with
changing wind conditions. Chironomid swarms are characteristically
columnar in form, as exemplified by the Chironomus at Delta Marsh
(Syrjamaki 1964). Females engage the mating process by entering the
swarms from their resting places on the adjacent vegetation. After
successfully mating, the females quickly leave the swarms and alight
on vegetation. So, while the female composition of a swarm at any one
time may be quite small (5% of the chironomids in a swarm), most
females in the vicinity will at one point enter the swarm.
Taken from: http://www.umanitoba.ca/faculties/science/delta_marsh/reports/1996/ellis.pdf
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