Spring Fishfly on Lamp Post

2023 June 4

Sam and I were walking to the hardware store downtown on June 3, 2023 when we spotted this very large insect on the concrete base of one of the lamp posts. These bases are concrete cylinders about 2 feet in diameter, and the insect was about the length and diameter of Sam’s little finger. Here is the picture cropped and rotated for a better view:

This is one of the two species of Fishfly that live around here, and I have had pictures one of them (the Summer Fishfly) twice before; once of a male that a friend of ours photographed up north of Calumet in 2014, and once of a beat-up specimen that I found dead beside the road in 2016 that was missing its antennae. This one appears to be a female, based on the fact that its antennae are threadlike instead of the big, bushy things that the males have. Given the time of year, I also think that this one is most likely the Spring Fishfly, Chauliodes rastricornis, given that both of those previous specimens were found in July while this one was in the first week of June. Unfortunately, I can’t quite see its head well enough to be sure, the Summer Fishflies have dark heads with a light-colored mark on the back of the head, while the Spring Fishflies have light-colored heads with a dark mark on the back.

We unfortunately didn’t have any camera available other than Sam’s cell phone, and didn’t have any way to capture it to take home for better pictures. Sam’s phone does have something of a macro function, though, so she was able to get some closer photos of the head.

So far, the only fishflies I have pictures of were just kind of hanging out on posts or walls during the day, implying that they most likely only fly at night. As big as they are, I expect that the bats think they are delicious. Of course, the size probably also means that they can lay a ton of eggs, so the larvae that live in the ponds and rivers are probably hundreds or thousands of times more plentiful than the adults.

They live as larvae for two or three years before coming out of the water to pupate, and then the adults only live for about a week as they mate and lay eggs. I need to fix up our aquatic net so I can see about finding some of the larvae.

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