Gold and Brown Rove Beetles prey upon Blow Flies

Subject: Help! Totally stumped with this insect!
Location: Newfoundland, Canada
September 16, 2013 5:37 pm
Hi there! I’m writing from Newfoundland, Canada. Today, sept 16, 2013 I came across an insect I have never seen before. I’m usually good with bugs – but this one has me stumped!
While walking through an alder bed with goldenrod I first observed the insect flying around and then landing on goldenrod. It looked a d behaved wasp like, pumping up and down. I never seen anything like it. Then I found a group of them ! They were attracted to a group of flies that had landed on something small and deceased. The flies were landing and walking on the carcass and the insects in question were skulking around – and then I watched one sneak up and grab a fly! Then I realized they were all doing this.
I had considered Robber Fly – but the antenna look totally wrong, so does everything else! But the behaviour is very similar! It’s predatory. I’d estimate the insect to be almost an inch in length.
Sorry for the long letter but I hope the details will help! Thank you so very much!!!
Signature: Jenny in Newfoundland

Brown and Gold Rove Beetle eats Blow Fly
Gold and Brown Rove Beetle eats Blow Fly

Dear Jenny,
This is one of the most exciting letters we have received in a very long time, and we are featuring it because of your thrilling personal observations and the gorgeous photos you have taken as proof of your observations.  In our untrained minds, you have made a significant scientific observation.  This is a Gold and Brown Rove Beetle,
Ontholestes cingulatus, and it appears to be preying on a Blow Fly.  According to BugGuide, the Gold and Brown Rove Beetle can be identified because it is “Large for a rove beetle. Dark brown and hairy. Clumps of hair forms dark spots on much of body. Yellow hair forms “belt” under thorax, covers parts of last abdominal segments. Head wider than pronotum. Eyes large, prominently placed on sides of head. Found on carrion and fungi. Often turns yellow tip of abdomen upward when walking.”  BugGuide also states its habitat is:  “on carrion wherever found” and “Eggs are laid near carrion or fungi,” but this is a rare BugGuide Information Page that does not discuss what the adult Gold and Brown Rove Beetle eats.  The large eyes are mentioned, and large eyes placed on the sides of the head would make a good hunter.  We suspect that the reason the Gold and Brown Rove Beetles are attracted to the Carrion is to prey upon flies as well as to lay eggs.  The developing Fly Maggots would compete with the larval Gold and Brown Rove Beetles’ food source, so eating the flies before they can breed on the carrion probably helps more Rove Beetles to survive to the adult stage.  Thanks again for your exciting submission.  We are going to feature it on our scrolling header as well.

Brown and Gold Rove Beetle preys upon Blow Fly
Gold and Brown Rove Beetle preys upon Blow Fly

Oh that’s so fascinating! Thank you for getting back to me so quickly!
It was just the most incredible thing watching those beetles hunt the flies. It took me by surprise at first! So I grabbed my camera and decided to photograph them grabbing and eating the flies. They moved so swiftly. They actually snuck up on the fly and then just grabbed them! There were about 7 of them around the carcass, and each one had a fly in it’s legs! So interesting! Especially since I never seen one before! I could have watched them for hours. Thank you so much for identifying this insect for me! I couldn’t figure out what it was and was going crazy! I’m so happy!
Many thanks!


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