What’s this bug
We are in Missouri, woke up to let the dog out and the yard was swarming with these. When I mean swarming I mean swarming. The entire yard, the neighbors yard as far as the eye could see they were everywhere. I left at about 9 am to take my daughter to camp. The entire subdivision was covered in them!! Any ideas? When we came back at about 10 there is significantly less of them but they are still out there. They are on the west side of the house only though not the east. Maybe they don’t like the sun? Thanks
Nikki Hickman

Hi Nikki,
You have been graced with witnessing the mass emergence of a species of Mayfly in the order Ephemeroptera. Adults only live a few days, their sole purpose in life being to mate and provide food to a vasy aray of other creatures higher up the food chain, like birds, fish and predatory insects. Larval Mayflies are aquatic, and live near a water source. Mayflies also are unique in that their are two adult forms, the subimago and the reproductive adult, known as the imago. We are also including a comment letter we got on a previous posting. You have pictures of a sloughed off exoskeleton and an adult. Perhaps one of our more knowledgeable readers can clarify if the adult is an imago or reproductive adult. If you are far from the water source, we are confident this is a reproductive adult.

Further Update: (04/26/2008)
Hi Daniel,
I sent in the comment several days ago about the mayfly imago and subimago; I’m a fly fisherman, among other things, and the mayfly picture with the shed exoskeleton jumped out at me. Interestingly, fly fisherman call the subimago stage of mayflies “duns” and the imago stage “spinners”. These are British terms, and I don’t know why they picked those words. … Your website is interesting, informative and fun, all at the same time, and I read it regularly. Thanks for your help.

Clarification: (07/19/2008)
Hi Daniel,
The picture of the adult mayfly from Missouri posted on July 16 is almost surely that of an imago rather than a subimago: the wings are clear, the tails are very long, and there is a shed exoskeleton. Mayfly subimagos typically have cloudy wings and relatively short tails, although no doubt there are exceptions to the rule. This insect is probably a species of the genus Tricorythodes. Fly fishermen refer to them collectively as “tricos”. They’re tiny, and it’s a challenge to tie a fly to imitate them and to fish it successfully. Tricorythodes emergences typically occur at night or early in the morning and the subimagos rapidly metamorphose into imagos; they mate, lay eggs, and die and it’s all over by noon.

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