Winter craneflies’ mating dance
IN the weekend, a man from South Dunedin brought to the museum some delicate small flies, similar in size to a mosquito, resembling the illustration.
These have been observed throughout Dunedin during the past week on mild, still winter days. Over shrubs and in gardens, lawns, and often within a metre of the ground, clusters of tiny flies were engaged in a strange dance.
Groups would oscillate up and down, sometimes passing through other groups, often oriented above a dead leaf or some other recognisable feature on the ground. They called to mind Ted Hughes’
Gnat Psalm:
When the gnats dance at evening
Scribbling on the air,
sparring sparely, Scrambling their crazy
lexicon,
Shuffling their dumb cabala, Under leaf shadow.
Leaves, only leaves
Between them and the broad
swipes of the sun. Leaves muffling the dusty
stabs of the late sun
From their frail eyes and crepuscular temperament. Dancing
Dancing
Writing on the air, rubbing
out everything they write, Jerking their letters into
knots, into tangles, Everybody, everybody else’s
yoyo.
These were winter craneflies (order Diptera, family Trichoceridae), primitive flies with long legs and very long antennae, like small craneflies, but with two ocelli on the tops of their heads, in addition to compound eyes. True craneflies (family Tipulidae) lack ocelli. Winter cranefly larvae eat dead leaves and fungi. The dancing groups consisted of males. Individual females would fly into the group, where some would mate, and others would occasionally fly out, very occasionally, with a male. They were thus behaving as leks.
A lek is a type of territory held by males of certain species, and used solely as a communal mating ground. Females enter such areas, and it often seems as though they are choosing a suitable mate as they move around within the lek.
Other groups of small flies such as fungus gnats and mosquitos dance in much the same way, but usually not in midwinter.