What insect is this? #618652 - Ask Extension


What insect is this? #618652

Asked March 24, 2020, 10:54 PM EDT

Is this a caterpillar or worm. What type?

Baltimore County Maryland

Expert Response

Good morning. Can you tell us where you found these insects? Where they in a yard, a natural area, or near a water source? Also, can you tell us how big/how long they are?

They might be robber fly larvae. Robber flies are good predators in the environment.
They are often found in rotten wood (tree roots, stumps, etc.).

I found hundreds of them under my deck on the concrete after a rain. I do have a raised wood pile under my deck. Also i has a lot of grubs last year in my grass. They are about 1 inch long and curl up like a grub when they die.
The Question Asker Replied March 25, 2020, 3:03 PM EDT
These have nothing to do with grubs in lawns. (Which are actually not a problem, unless you have about 10 per square foot in a drought.)

These are robber fly larvae.  Robber flies are predator insects, that eat pest insects, so they are beneficial.  Also harmless to humans and animals.  

Since the larvae live in damp rotten wood and eat other insects, they probably fell or washed out from your wood pile where they were eating other insects.  In a natural setting, that's good.  

 This means some of the wood is probably rotting and damp, so you may want to remove very old rotting wood (which isn't good firewood anyway) and dry up the area, if possible.  Maybe put a tamp over the pile.  

In the past, you may have simply thrown wood on the fire that contained these and never knew the difference.  

Thank you so much.
The Question Asker Replied March 26, 2020, 10:32 AM EDT
Our pleasure. 

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