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Feathery Antennas - Macrosiagon limbata - male

Feathery Antennas - Macrosiagon limbata - Male
Northern, Virginia, USA
July 8, 2004
This was taken in a power line cut that is "managed for wildlife". It was less than a centimeter long.

I don't even know where to start looking. Can anyone point me in the right direction?


Macrosiagon compare limbatum
As mentioned by others, this appears to be Macrosiagon. There are illustrations and a key in Arnett, How to Know the Beetles. (1) See Identification section of guide page for details.

I agree with Troy's previous comment--this resembles M. limbatum, illustrated and described by Arnett, How to Know the Beetles, p. 283, fig. 668. (1) Other photos submitted appear to be this species as well.

Patrick Coin
Durham, North Carolina

Macrosiagon limbata (Fabricius 1781), male

Your determination is spot on- this is a male specimen of M. limbata, as are photos 8008 and 8009. It is probably the most commonly encountered ripiphorid in North America and is widespread in Eastern North America down to Central America. I don't don't believe it's known from the West Coast.

Like most Macrosiagon and Ripiphorus species, M. limbata varies enormously in size and coloration, often confusing people. There is a closely related species, M. lineare (LeConte 1866) that is also Eastern US in distribution, though it is much, much more rare. In fact, I am inclined to believe they are the same critter.



Slender Mountain Mint?
Is that Slender Mountain Mint (Pycnanthemum tenuifolium)? If so, this page lists several species of beetles that visit:
Flower-visiting Insects of Slender Mountain Mint
Including these rhipiphorids:
Macrosiagon dimidiata, Macrosiagon flavipennis, Macrosiagon limbata

The Macrosiagon page of the NCSU insect collection lists all those with respectable counts, limbata having the most.

I'm searching for some photos.

Macrosiagon limbatum?
OK, How to Know the Beetles (1) gives the following description for M. limbatum (which I assume to be the same as M. limbata):
"Head, thorax, under surface, femora and middle and hind tibiae reddish yellow; thorax with oval black spot on disk. Elytra either entirely black or with pale yellow centers."
That closely matches your photo. There's also a description for M. dimidiatum that rules it out.
That's a lot of circumstantial evidence, so I'd say this is likely that one.

Wedge-shaped beetle
Yes, it is a beetle in the family Ripiphoridae ("they" changed the spelling, it was formerly Rhipiphoridae). Your image is of a male in the genus Macrosiagon. These beetles are parasties of solitary bees and go through hypermetamorphosis. Typical scenario: Female beetle lays eggs on flower. Eggs hatch into active larvae called "triungulins." At least one larva will grab onto a pollen-foraging bee, and get a ride to her nest. Larva disembarks (de-bees?), invades a cell in the burrow and attaches to the bee larva. Eventually, the larval beetle becomes a grub-like "couch potato" before pupating and then emerging later as an adult. Bizarre.

Maybe Rhipiphoridae
It looks somewhat like a tumbling flower beetle (Mordellidae), so I checked my Peterson's Beetles (1) and noted that Rhipiphoridae was a similar family. Checked that family there and it looked promising. Then I checked the family description in Arnett (2) and he said similar to Mordellidae, but with blunt abdomen, pectinate or flabellate antennae, and black and orange. Sounds promising.

This page has an illustration (Macrosiagon) showing the similarity to yours.

I did some brief online searching but didn't turn up anything.

I believe there were some others in this family posted recently, but without the feathery antennae.

Thanks Troy and Eric
Fascinating stuff.

I don't think that was Slender Mountain Mint, but it attracted Peck's and Least Skippers, and a couple other Skippers.


Wedge-Shaped Beetles
Hey All,

With Eric and Pat's homework, we did find out that I had recently taken pics of a similar species:

...I do have shots of a similar species (taken at the same area) from last fall with the feathery antenna as well, so it could be the male.

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