Last week on our daily walks we noticed several of these black oil beetles along the road side and in the open fields near our home. They are very large and we were not sure what they were. A strange beetle or extremely strange ants?
Upon researching what we found we were amazed to find these are flightless Beetles with a truly fascinating life cycle.
Encyclopedia of life describes the lifecycle as follows:
“Oil beetles have fascinating life-cycles. The larvae are parasites of a number of species of ground-nesting solitary bee. Towards the end of spring, female oil beetles dig burrows in the ground close to colonies of host bees, into which they lay around 1000 eggs. These eggs usually hatch the following year in order to coincide with the emergence of the bees. The oil beetle larvae (known as tringulins) are very active, and climb up onto flowers where they wait for a host bee. They attach themselves to the bee, and if they are lucky and attach to the right type of species they will be flown to the host’s burrow, where the tringulin oil beetle turns into a grub-like larva, and develops, feeding upon the pollen stores and eggs of the host. The larva pupates and the resulting adult beetle spends the winter inside the host’s burrow before emerging the following spring.”
We think this female might have been building a nest to lay her eggs?
Piotr Nasckrecki wrote a wonderful article on them on his blog The Smaller Majority which is altogether fascinating.
While we saw several oil beetles last week we only had the opportunity to photograph one, which like the others, was constantly on the move but moving slow enough for us to photograph.
nature has no boss 
Interesting info. and nice macro photos Mike.
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Thanks Rob, it is always fun to find anew and interesting creature to study.
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I just saw some last week while out on a hike. I have spent quite a bit of time in high desert environments and had never seen them before. An odd and interesting creature. Thanks for more info about them!
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Hi and thanks we found these beetle odd as well and use an aside we saw one again this morning while out jogging. I think in the past they were limited in the western US but seem to be moving more westward each year.
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Yes, you may be right. I saw them near Smith Rock State Park in central Oregon.
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Splendid creature.
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Interesting… seems the beetles don’t harm the bees… well, hopefully they leave them some food! 😉
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This is a class of insects I knew nothing about. I’m glad you provided the link to more information about them.
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Hello, sorry to post on an old topic, but just saw one earlier today in Delaware on my walk. Thought it was a Rove beetle at first, but apparently it is the same kind you saw. They are big, I want to say the size of a nickel or quarter
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