Giant Elm Sawfly

2016 December 7

I found this large insect dying on the side of the road on June 25, 2016. Its body was close to an inch long, and it was so far gone that it did not resist being picked up at all, it would just occasionally move a leg feebly or occasionally turn its head.


I’ve actually found similar sawflies twice before, although looking at those now I see that they aren’t quite the same – both of the previous specimens have orange abdomens instead of black with white spots, and one of them has black antennae, while this one’s antennae are pale orange.


The one we are looking at today also does not have unusually “beefy” legs, so it is most likely a female rather than a male.


It was resting with the wings closed at first,


but it had enough life in it yet to eventually spread its wings, showing the prominent white spot on its back.


So, anyway, unlike the last two times where I wasn’t quite sure of the ID, this time I am pretty sure that it is, in fact, the Elm Sawfly, Cimbex americana. In spite of the common name, its caterpillars are not restricted to elm, it will also eat willow, maple, birch, and basswood, all of which are way more common around here than elm. It is kind of interesting that I always seem to find them lying around dying. As big and juicy-looking as they are, one would think that they’d get snapped up by predators so fast that they would rarely get the chance to die of old age, and yet that’s the only way I see them. Which leads me to suspect that they probably aren’t actually as delicious as all that. And, in fact, their larvae defend themselves by spraying noxious chemicals, and I see no reason why the adults would not retain these chemicals to make themselves unpalatable as well.

Although, another reason why I only see the old, dying specimens is that the adults evidently don’t get nectar from flowers. Instead, they hang out in trees where they strip the bark from twigs and drink the sap. And, since they are way up in the trees instead of down near the ground, I don’t see them until they lose the ability to fly or hang on, and fall down.

2 Responses
  1. December 9, 2016

    I wonder what finally gets them. Arterial sclerosis from all that sap, perhaps?

  2. December 12, 2016

    Whatever it is that kills them, I doubt that there is a close analog in humans. I mean, insects don’t even really have hearts, or lungs, or much in the way of brains, and failures of those organs seem to be mostly what kills humans. I expect what gets the old insects is probably something more like toxin accumulation, depletion of fatty reserves, breakdown of whatever organs they do have, and a sort of general gratuitous existence failure.

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