Dumpster diving xanthopygine rove beetles

Let's face it, a lot of beetles are associated with ants. But few go to the extremes that rove beetles go to make themselves at home with the ants. Many rove beetles not only look like ants, they also smell like ants. If you want to see some really cool, yet ultimately bizarre beetles, I suggest you read the blog post by Joe Parker and Taro Eldredge on Pselaphinae and Aleocharinae myrmecophiles.

A few xanthopygine rove beetles are known to be associated with ants but these beetles are typically found on ant refuse piles (=dumpsters). The refuse piles are nutrient-rich, thriving micro-communities that support many types of arthropods, fungi and bacteria. Most rove beetles are there to feed on the fly larvae but we really do not know the details. Navarrete-Heredia (2001)* lists 65 genera (148 species) of rove beetles associated with leaf cutter ants, either Atta or Acromyrmex. Several xanthopygine beetles made the list, including species from the genera Glenus, Paraxenopygus, Tricholinus, Scariphaeus, Smilax and Plociopterus.

Glenus jelskii Solsky is known from refuge piles of Atta sexdens (Scheerpeltz 1936)

One striking feature of all these xanthopygines is that they are good-looking beetles. I would have expected that an insect hiding in a refuge pile would be dull-colored (why spend energy on coloration?) but most of these have shining metallic colorations with bright yellows and reds. Not sure if this is a plesiomorphic characteristic (most xanthopygines have impressive metallic coloration) or if there is an adaptive significance of the coloration.

Some xanthopygines take their Hymenoptera associations one step further: they are known from debris piles of wasps and stingless bees. One of largest (almost 3 cm) known xanthopygine rove beetle, Triacrus dilatus, is known from the debris piles of the wasp Stenopolybia Agelaia vicina (Wasmann 1902).

Triacrus dilatus Nordmann

A couple more species, Xanthopygus cyanipennis and Xenopygus analis have been recorded from the nest of Trigona clavipes (a stingless bee) (Luderwalt 1917), although both of these instances might be accidental/opportunistic. Xenopygus analis is extremely widespread (Mexico to Brazil, introduced in Hawaii) and will feed on anything. A while back I posted a video clip of X. analis eating rotting Gustavia superba fruits.

A lot of cool work remaining to be done here, both systematic and ecological, to understand these associations and map the evolution of these behaviors.


*Thanks to Adam Brunke for providing some of these references.

References

Luderwalt H (1917) Biologishes uber brasilianische Staphyliniden. Z. Wiss. Insektenbiol. 13: 44-47

Navarrete-Heredia JL (2001) Beetles associated with Atta and Acromyrmex ants (Hymenoptera: Formicidae: Attini). Transactions of the American Entomological Society 127(3): 381-429.

Scheerpeltz O (1936) Die von Prof. Dr. H. Eidmann gelegentlich seiner im Jahre 1933 nach Brasilien unternommenen Studienreise aufgesammelten Staphyliniden. I. Die in den Nestern von Atta sexdens L. aufgefundenen Staphyliniden, nebst einigen Bemerkungen uber die Gattung Scariphaeus Er. Archiv fur Naturgeschichte (N.F.), 5, 483–540.

Wasmann E (1902) Riesige Kurzflügler als Hymenopteren-Gäste. (132 Beitrag zur Kenntniss der Myrmekiphilen und Termitophilen.). Insektenborse 19: 267–268, 275–276, 282.

The limits of morphology

I was told early on as a graduate student that an insect taxonomist should "kill first, ask questions later" during fieldwork. This was usually said in the context that you might lose a rare specimen if you spend time looking at it, rather than putting in a vial. I am here to tell you that I have deeply regretted following that advice.

Every single time I am working on a taxonomic paper I catch myself having the same wish: "I wish I had seen these specimens alive, just to get a glimpse of how they are using these structures." Morphology can tell us a lot of things but sometimes a dead insect hold its secrets very well.

Exhibit A: In a paper published in 2005, Steve Ashe and I revised the genus Philothalpus. These are striking beetles with questionable taxonomic affinities (at least according to DNA).

Philothalpus brooksi

Abdominal sternum VII

Males in this genus have a perplexing structure (indicted by a white arrow on the figure above) on the ventral side of their abdomen, specifically on the 7th abdominal sternum. Back then we called it a "porose structure". Truth is, we have no idea what it is. A hole on the body with setae around it. Only males have it. But how do they use it? I have no clue. I guess I will be inclined to accept the notion that is used in male/female interactions since it is only present in males but, boy, if only I had seen these guys alive...

The example above came to mind when I recently examined a species (in another genus) with a similar structure:

Exhibit B:

 The structure is present in the same abdominal segment (VII) but it is clearly different than the one above. Are these structures homologous?  Are they used for the same purpose? Morphology cannot answer these questions. Sure, we can do fancy evo-devo here, but that requires live specimens, identifying conserved developmental genes and so on.

What we really need is good old basic natural history observations that can solve these problems. But "kill first, ask questions later" attitudes really do not help. So, next time you are in the field, jot down some observations before you kill those insects.

Do xanthopygine rove beetles eat fruit?

It's been a long time since the last post, but I was out for good reasons: end of the semester craziness, grading a mountain of exams, working for a three letter (scientific) government agency and on top of all  these a sick child. Now I need to start the paper writing machine for the summer.

I have been uploading several video clips of rove beetles on figshare and you can see many of those here Almost all of those are from my graduate school days and were shot on Barro Colorado Island in Panama, either in 2000 or 2001. I used some of the data to write a paper on Nordus fungicola natural history (a link to the paper is here).

Here is a clip of another Xanthopygine rove beetle (Xenopygus analis) munching on rotten Gustavia superba fruits. Almost all xanthopygine rove beetles are considered to be carnivorous, but I guess there are always exceptions out there.

                                             http://dx.doi.org/10.6084/m9.figshare.693731

Here is a more typical example of feeding behavior,  a male Nordus fungicola stealing a prey item from an ant (no idea what this is) and then proceeding to chew (technically speaking, this is extra oral digestion) the fly larva.