Beetle Morphology

NikonUser · Post by **NikonUser** » Wed Sep 30, 2009 4:31 am

This is Agoliinus leoparus, a dung beetle.
Length: 6.5mm
El Nikkor 63/2.8 @ f/6.7, 0.2mm frames stacked with Zerene Stacker PMax

NU09188
Beetles are one of the most species diverse groups (Order) of living organisms with more than 250,000 species described and about 30,000 in NA separated into many families.

When asked by a theologian about what could be concluded about the Creator from a study of creation, the evolutionary biologist J.B. S. Haldane replied that He has "an inordinate fondness for beetles".

The Scarab beetles (Family: Scarabaeidae) with many thousands of species can be immediately separated from all the other beetles by the structure of their antennae: 3-7 plates that form an apical club (lamellate antenna). Plates are 'compressed' when beetle is resting, open when active.
El Nikkor 50/2.8 @ f/5.6 , ventral @ 0.1mm frames, dorsal @ 0.05mm frames; ZS Pmax

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So far: Beetle (Order: Coleoptera); Scarab (Family: Scarabaeidae).

Next level is the Aphodiine Dung Beetles (Subfamily: Aphodiinae)
Characters include
- clypeus (a shield-like plate on the front of the head) expanded and notched at apex (see 2nd set of images, above; and ventral view, below) such that the mandibles not visible from above; in fact can see very little of the head from above, perhaps the antennae and the front dorsal 1/2 of the eyes.
- hind tibia with 2 spines.

The genus Aphodius characters include:
- keel-shaped ridges on mid and hind tibiae.

Habits: the beetles feed on humus or dung. The front of the head probably acts to push into the humus/dung and direct it over the beetles back; the powerful front legs have the tibiae modified into digging paddles that propel the beetle forwards (fossorial front legs).

Leg images: 4x Nikon CF N Plan Achromat, frames @ 0.02mm; Zerene Stacker P Max

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Harold Gough · Post by **Harold Gough** » Wed Sep 30, 2009 5:56 am

It looks like an ad for French Polishing. Very handsome.

NikonUser · Post by **NikonUser** » Wed Sep 30, 2009 6:56 pm

Know anyone who would pay for its use in advertising

rovebeetle · Post by **rovebeetle** » Thu Oct 01, 2009 2:09 am

Very nice Aphodius images. I like that genus, but I always had a weakness for speciose taxa - no wonder I ended up working on Staphylinidae

.

But may I update your numbers, if you don't mind?

Right now, we have arrived at about 400.000 described beetle species.

Cheers

NikonUser · Post by **NikonUser** » Thu Oct 01, 2009 7:36 am

Thanks Harry for the ID, I thought that is what it is.

Speciose taxa are ideal for the professional entomologist/taxonomist but for us regular 'Joe photographer' the monotypic genera are ideal.

Seems there are round 200 spp. of Aphodius in NA which really lowers the likelyhood of getting my bug down to a species.

Your Avatar looks like a scarab (dung beetle perhaps); conflict of interest?

rovebeetle · Post by **rovebeetle** » Thu Oct 01, 2009 8:08 am

NikonUser wrote: 'Joe photographer'

That's not what I would call you when looking at the quality you deliver

NikonUser wrote: Seems there are round 200 spp. of Aphodius in NA which really lowers the likelyhood of getting my bug down to a species.

Don't know about NA but the color pattern looks like a group of species which is very difficult to identify (probably only by genital) - at least this is what they are here in Europe.

NikonUser wrote:Your Avatar looks like a scarab (dung beetle perhaps); conflict of interest?

That is Onthophagus taurus. No conflict here, but one of the very few beetle photos I have which fit into a square and are not preparated like an illustration

Cheers

NikonUser · Post by **NikonUser** » Thu Oct 01, 2009 12:08 pm

New edits do not show as a "Last Post", this does

rjlittlefield · Post by **rjlittlefield** » Thu Oct 01, 2009 12:45 pm

Lovely pictures, but I'm unclear what "notched at apex" means.

In How to Know the Beetles, there's a key entry that says "14a Clypeus notched at sides in front of eyes, exposing base of antennae". That description doesn't seem to match what's shown here, but I can't get my eyes on anything else that I'd call a "notch".

Can you point to it?

Thanks,
--Rik

NikonUser · Post by **NikonUser** » Thu Oct 01, 2009 1:32 pm

'My' beetle is an Aphodius in the SF: Aphodiinae; my original ID and confirmed by rovebeetle.

Borror, Triplehorn, Johnson. 1989. An introduction to the Study of Insects. 6th Edn.
p 421: "Clypeus expanded, mandibles not visible from above, clypeus usually notched at apex . . . . . . . Aphodiinae.

I interpret the concave edge at the center front of head as "notched at apex". The little bits sticking out in front of the expanded clypeus are palpi (possibly maxillary palps).

There are a couple of notches at the back that expose a bit of the eyes but there is no way that the base of the antennae can show in this species (see ventral beetle).

rjlittlefield · Post by **rjlittlefield** » Thu Oct 01, 2009 2:09 pm

I considered that concavity at front, but I understand the term "notch" to be an abrupt indentation, versus a smooth curve. The other thing I considered is the dent in the middle of the clypeus, at x=774,y=83 in your first image and x=539,y=98 in your second image. I also don't feel confident that I understand what "apex" means here, since I understand to that term to mean the highest point of something, or at least the most extreme point, and that opens several possibilities.

I'm sure these terms mean exactly what the original author chose them to mean, neither more nor less (with apologies to Lewis Carroll, Through the Looking Glass). But they don't necessarily mean the same thing to somebody else. That why illustrations like these are so nice, now that they're finally practical.

I'm not challenging the ID, by the way. I'm just trying to understand how the words relate to the picture. And there's no compelling reason why I need to get clear on exactly what this notch is. I just though you'd be interested to know that I'm not clear about it, and some hints about why that is.

--Rik

NikonUser · Post by **NikonUser** » Fri Oct 02, 2009 8:52 am

Rik:
What a can of worms! What appeared to be a relatively simple key character and an obvious Aphodius has turned out to be not so. Multiple genera in the SF and even more species.

An incredible recent (May 2008) internet resource from the University of Nebraska State Museum
"Generic Guide to New World Scarab Beetles"
The subfamily Aphodiinae begins:
HERE
Could not find any mention of a "clypeus notch at apex".

An interesting diagnosis on The Discoverlife site
HERE
that includes:
1) Clypeus extends over mouthparts, hiding them from above; clypeus often notched or concave along front edge

Anyway, I contacted Dr. Skelley and he ID'd the beetle as Agoliinus leopardus.

rjlittlefield · Post by **rjlittlefield** » Fri Oct 02, 2009 10:38 am

Fascinating! Thanks for the followup and links.

Yes, I see what a can of worms this group is. Quoting from the first link you give, but with emphasis added:

Head with clypeus usually expanded, usually covering mouthparts. Mandibles often reduced. Antennae with 9 segments, club 3-segmented. Mesocoxae usually nearly contiguous, with notable exceptions. Metatibiae usually with 2 apical spurs. Abdomen with 6 visible sternites. Pygidium partially or completely covered by apex of elytra. Tarsi usually with distinct claws.

Perhaps this group becomes more clear with familiarity. But it seems very challenging indeed to write a key around features that apparently have so many exceptions and ambiguities.

Adding to the confusion, I see that BugGuide still represents Agoliinus as a subgenus of Aphodius.

--Rik

NikonUser · Post by **NikonUser** » Fri Oct 02, 2009 11:58 am

Rik:
I missed the really significant part of that diagnosis, and I guess you did too.
It's "Pygidium ... covered.... [wait for it, drum roll] by APEX of elytra.

The pygidium is the last dorsal segment of the abdomen.

So apex means 'end of', 'tip of ' but not highest point.

Q.E.D.

rjlittlefield · Post by **rjlittlefield** » Fri Oct 02, 2009 12:39 pm

Actually I did notice that. And I looked at elytra in pictures of this group and observed that they have obvious tips at or near the end of the abdomen. So I don't feel uncertain about what "apex" means in that case.

However, when the front of the clypeus is so broadly concave that it no longer has a single tip, but rather two tips separated by 1/3 the width of the entire structure, then I'm not at all certain what "notched at apex" might mean when that's all I get to read.

Putting all of this together, I'm guessing that the person who originally wrote "notched at apex" was a) influenced by species that have a more abrupt concavity, and b) distinguishing against an alternative that would be something like "front of clypeus straight, broadly convex, or pointed".

In any case, my real point is that high quality annotated photographs add a lot to the usefulness of keys. With images as good as yours, well equipped with arrows, perhaps even I could fumble my way through without going astray too often.

--Rik

Barry · Post by **Barry** » Sat Oct 03, 2009 1:09 am

NU,

Very nice work!
Are there good papers dealing with the functional morphology for digging in beatles?

Cheers,
Barry