Maddening mutillid

Traumatomutilla graphica (Gerstaecker, 1874) | Parque Nacional Chaco, Argentina

During my stay in Corrientes, Argentina, I had two distinct biomes to explore—the relatively moist “Selva Paraguayense” to the east in Corrientes Province (a southern adjunct to the Atlantic Forest of southeastern Brazil, and home to the cryptic longhorned beetle that I featured in Desmiphora hirticollis: Crypsis or Mimicry?), and the drier “Gran Chaco” to the west, home of the insect featured in today’s post. Precious few remnants remain of the original Gran Chaco, which once covered nearly 1 million square kilometers in northern Argentina, Paraguay and Bolivia and the best example of which can be found at Parque Nacional Chaco in north-central Argentina. I’ve already mentioned that conditions are typically quite dry by early April in northern Argentina, and this is especially true of Chaco Province, where droughts during the months of January through March are common. As a result, I didn’t expect to see much insect activity during my visit last month. For the most part this was true, but one insect I did see at several points along the trails through the park was this rather large velvet ant (order Hymenoptera, family Mutillidae). Not an ant, of course, but a true wasp, these insects must be treated with respect as they are capable of delivering a painful sting. This, combined with their ceaseless, erratic wanderings makes them incredibly difficult to photograph. However, with few other insects to see, I thought I would spend the time and effort to see if I could get some good field photographs of this very attractive species. I spent about half an hour attempting to photograph it by panning through the viewfinder while getting closer and adjusting the focus on the move, and then firing shots when I thought I might be close enough and had the individual more-or-less within the frame. This was wildly unsuccessful, as I had only a 3-ft wide path within which to work and had to constantly get up to block its escape into the adjacent vegetation. Moreover, it was exhausting! The constant moving and body contortions while in crouched or kneeling positions used muscles I didn’t even know I had (but was well aware of the following day by their soreness!). Out of the countless shots that I fired, these two photographs are the only ones that I consider worthy of posting—pretty good, but not great.

The distinctive color pattern is diagnostic for the species.

According to Kevin Williams (many thanks!), the distinctive color pattern readily identifies this individual as Traumatomutilla graphica (Gerstaecker, 1874). Nearly the size of our common eastern North American Dasymutilla occidentalis (a.k.a., cow killer), the bold, conspicuous patterning surely must serve as advertisement of its powerful defensive capabilities—I know I was deterred from trying to handle it. Kevin mentions it as a “great find!” and that the male of the species is still unknown, and I could find nothing about the biology of this species. However, mutillids in general are known to develop as external parasitoids of various wasps, bees, beetles and flies, the excessively long female ovipositor enabling piercing of host nest cells before injecting their powerful venom and placing the eggs (Hogue 1993).

REFERENCE:

Hogue, C. L. 1993. Latin American Insects and Entomology. University of California Press, Berkeley and Los Angeles, 536 pp.

Copyright © Ted C. MacRae 2012

Pseudomyrmex in Corrientes, Argentina

Early April is early autumn in northeastern Argentina, but seasons just south of the Tropic of Capricorn bear little resemblance to the well-defined spring, summer, fall and winter that we are accustomed to in eastern North America. Early fall here is not a riot of color, pungent smells, and sharp shadows cast from an oblique sun, but rather dull greens and browns, muted and dusty after eight months under a searing overhead sun with only the sparsest of rains for the past two. Such conditions are generally not conducive to insect life, and for the most part insects that live in warm, seasonally wet environments adapt by timing their adult activity (the time for reproduction) to the moist seasons—which in this part of Argentina means September through January. Thus, despite warm temperatures and a subtropical environment, early April is not the best time to be looking for insects here.

Pseudomyrmex sp. | Corrientes, Argentina

Nevertheless, not all insect groups respond in this fashion, and one in particular is as ubiquitous and diverse now as at any other time of year—ants! I had to trek into sand and mud along the Rio Paraná to find tiger beetles (a few), and it took some dedicated searching to ferret out a few stands of late-season blooming plants and fresh-cut woodpiles to encounter a small diversity of longhorned beetles. I think I may have even seen a single jewel beetle, a chrysobothrine of some type, as it landed on and then flash flew away from the same woodpile with which I had modest longhorned beetle success. The ants, however, have been everywhere—no tree, shrub, or square meter of ground is without them in astounding diversity of size and form.

At this point it appeared to be eating something it plucked from the bark.

I probably shouldn’t admit this, as I hear rumor there are a few myrmecologists that frequent this blog, but I have a hard time getting excited about ants. I know, their unique social structures and evolutionary history are among the most fascinating in the insect world, and watching their behaviors is a lesson in charisma beyond reproach. Still, however, for me there are just so many of them and their taxonomy so completely foreign to me that every time I try digging further I feel immediately overwhelmed. Coleopteran taxonomy may be an order of magnitude more diverse, but since I only pay attention to about 1.5% of the order, it’s as comfortable to me as an old shoe.

Close...

There is one group of ants that I do find endlessly fascinating—the genus Pseudomyrmex. I don’t know why that should be the case—there are plenty of other ant genera that seem to have the tools and structures that usually grab my attention (e.g., grossly oversized mandibles, sharp spines, heavy duty surface sculpturing, etc.). Pseudomyrmex spp. have none of these morphological gimmicks—just a simple, elongate, wasp-like form. Perhaps it’s their association with branches (like wood-boring beetles) rather than the ground—nope, tiger beetles are decidedly ground dwellers and I dig them (Get it? Heh!). No, it must be their super-sized eyes. Most ants have beady little eyes that make it hard to look into their soul. Pseudomyrmex eyes have charisma—you can see them looking at you (and almost read their thoughts).

closer...

Anyway, among the many ants that I’ve noted wandering the banks of the Rio Paraná here in Corrientes are these smallish, orangish Pseudomyrmex spp. This particular individual was the first one I saw, revealed when I happened to pull away a bark chip from trunk of the palm tree on which it was hiding. It wandered all over the palm trunk for the next 15 minutes or so as I chased after it with my 65mm lens. For such tenaciously crawling subjects I’ve found that simply firing off shot after shot as you track it in the view-finder rather than waiting for it to pause and trying to compose each shot is the best way to get some usable images. It’s simply a numbers game—the more shots you fire off, the better chance you have that at least some will be in-focus, nicely composed, and well-lit. These are the ones I was happiest with from the session. (And, OMG, did I really just give advice on how to photograph ants?)

Closest!

It goes without saying that a more specific ID, if possible, would be greatly appreciated (should any prominent myrmecologists happen across these photos). There are scads of species in this genus right across the river in Paraguay, and presumably the diversity in Argentina is similarly high.

Copyright © Ted C. MacRae 2012

Leafcutter ants on corn

Leafcutter ants attacking corn | western Buenos Aires Prov., Argentina

North American corn farmers certainly have their share of insect pests to worry about. Between corn borer, earworm, armyworm, and rootworm, there isn’t much of the plant that isn’t vulnerable to attack by at least one of these insects. Argentina corn farmers have all this and more—have you ever seen ants attacking corn? I took these photographs yesterday in a corn field in western Buenos Aires Province showing leafcutter ants dining on the developing kernels of late-planted corn. Okay, “dining” may not be the proper word, as they are not actually eating the kernels, but rather harvesting them to bring them back to their “hormiguera” (ant nest) for cultivation of the fungi on which they feed. The four pairs of spines on the pro-mesonotum and narrow distal antennal segments suggest this is a species of Acromyrmex, three species of which are mentioned as pests of corn in Argentina (A. lundii, A. striatus, and A. lobicornis). Of these, the individuals in these photos seem to best match AntWeb’s photos of Acromyrmex lundii, but that is just my guess.

Acromyrmex sp. poss. lundii?

Copyright © Ted C. MacRae 2012

The Methocha

As pointed out in my recent post, Bee Fly Parasitism of Tetracha virginica, there is much to learn still regarding tiger beetle larval parasitoids. In addition to bee flies (order Diptera, family Bombyliidae) of the genus Anthrax, tiphiid wasps (order Hymenoptera, family Tiphiidae) in the genus Methocha also parasitize tiger beetles in their larval burrows. Unlike bee flies, however, which sneakily lay their eggs in and around tiger beetle burrows when their victim isn’t watching, Methocha females aggressively engage the larva and even allow themselves to be grasped within the beetle larva’s sickle-shaped mandibles in order to gain entry to the beetle’s burrow.

Methocha appears to be a rather diverse genus, but it’s taxonomy is still incompletely known. George Waldren from Dallas, Texas is working on a revision of the genus and has found several new species in Texas alone. George is interested in seeing Methocha material from other areas as well and recently sent me the following reminder that adult females are active now:

…if you know of any areas with many tiger beetle larvae, now is the time to find Methocha. They superficially look like Pseudomyrmex ants, but once you see one you’ll catch on to them quickly. I collected more than 70 females today in a large aggregation of Tetracha carolina burrows.

In a subsequent message he adds:

Collect as many as you can, since they seem to be highly seasonal and rare most of the year. I almost always find them around beetle populations in sandy creek beds and receding bodies of water. A pooter works best if they are abundant and there isn’t much for them to hide under. Using your fingers also works—the sting is mild and usually doesn’t pierce the skin (depends on the person and size of the wasp). Vial collecting one by one works just as well.

Methocha females are generally overlooked due to their specialized life history and few specimens are in collections. Males are better represented since they’re easily collected with malaise traps.

If you have any Methocha specimens or manage to collect some, please contact George (contact info can be found at his BugGuide page). BugGuide does have a few photographs of these wasps to give you an idea of what they look like, but this excellent video titled “The Methocha” from Life in the Undergrowth with David Attenborough provides an unparalleled look at their appearance and behavior:

Copyright © Ted C. MacRae 2011

BugShot 2011 – Final Thoughts

As I suspected would be the case, ID Challenge #11 has proven to be an especially difficult challenge.  As a result, instead of posting the answer tonight I’m going to give folks another day to make their play for points (remember, nobody walks away empty-handed).  In the meantime, I’ve had a chance to ruminate over this past weekend’s BugShot insect photography workshop at Shaw Nature Reserve in Gray Summit, Missouri, and now seems to be an appropriate time to post some final thoughts while they’re still fresh in my mind. Suffice it to say that it was an incredible experience—both technically and socially.  I learned far more than I thought possible (and hope I can remember even a portion of it) and made some great friends in the process.  It’s really not possible for me to summarize here all of the techniques, insights, equipment choices, etc. that were covered, nor do I want to—such a list would be boring to read and not very meaningful without the context to go with it.  What I would like to do is shout out a few people who, beyond the collective, helped make the weekend what it was for me.

Instructors.  The three instructors, all accomplished insect photographers of the highest caliber, typified three very different yet complimentary approaches to the art.  Alex Wild (University of Illinois), ant photographer extraordinaire and author of the insect blog I’ve most tried to emulate, gave me tremendous insight on lighting and practical approaches on how to use it effectively.  My discussions with John Abbott (University of Texas) about equipment will be very helpful for the type of photography that I like to do (I’m not sure I’m ready for the tripod yet, but maybe the other ideas we discussed will be the “slippery slope”).  Finally, I thoroughly enjoyed my time with Thomas Shahan (Norman, Oklahoma), whose great artistic insight helped me see a whole new world of possibilities for tiger beetle portraiture.  I must admit to feeling a little star-struck when I first began talking to him, but his infectious enthusiasm and exuberance quickly put me at ease.

Friends.  I can’t begin to list everybody whose company I enjoyed, but standouts include Jo Holly (Alex’s better half!), as well as fellow bloggers Crystal, Lee, Dave, and DragonflyWoman.  Even though I only met them this weekend, it was if I had known them for years.  My time “fishing” tiger beetle larvae with Crystal and Lee was not only a highlight of the trip (watching them “jump” as the larva came flying up and out of the burrow was a real treat), but also represented a discovery in the truest sense of the word (as will become clear in a future post).  No discussion of friends would be complete without mentioning James Trager, not only for opening up Shaw Nature Reserve to this weekend’s event, but also for the access he’s given me over the past several years and our frequent, humorous email discussions about all things entomological (or botanical, ecological, etc.).

Gratitudes.  I want to thank Alex for inviting me to take part in this event as something more than just an attendee.  I hope my contribution, however small, was beneficial.  My thanks also to Patsy Hodge, who was so helpful and gracious to me in the days leading up to and during the event.  I also appreciate the kind comments that many of the attendees made to me about my blog and my photographs—your encouragement means a lot to me.

Regrets.  In an event like this, packed as it was with seminars and group discussions, it is sad but unavoidable that one cannot spend at least a little time with each and every person in attendance.  To those that I did have a chance to talk to, the pleasure was all mine.  To those that I missed, I will catch you next time!

I think I’ll close with this minimally processed photograph of what I take to be Misumenoides formosipes (whitebanded crab spider) and its honey bee (Apis mellifera) prey.  Although I photographed this spider using flash and looking straight up into an overcast sky, I managed to properly illuminate the subject and avoid blown yellows and an all-black background by using some of the very techniques and principles that I had just learned earlier that day.  I hope to learn more at BugShot 2012!

Misumenoides formosipes (whitebanded crab spider) | Shaw Nature Reserve, Franklin Co., Missouri

Predator or Prey?

Ellipsoptera hamata lacerata | Dixie Co., Florida

Everyone knows that tiger beetles are predators, but look closely at the underside of the head of this female Ellipsoptera hamata lacerata (Gulf Beach Tiger Beetle), photographed in a coastal marsh in Dixie Co., Florida earlier this month.  See the ant head attached by its mandibles to the base of the tiger beetle’s left maxillary palpus?  Detached ant heads latched onto the palp or antenna of a tiger beetle are a fairly common sight—Pearson and Vogler (2001) show the head of an ant attached to the antenna of Eunota togata (Cloaked Tiger Beetle), and Pearson et al. (2006) show one attached to the antennae of Cicindela formosa (Big Sand Tiger Beetle).  I’ve also photographed Cylindera celeripes (Swift Tiger Beetle) with an ant head attached to its antenna.  Pearson and Vogler (2001) and Pearson et al. (2006) both suggest that the ant heads are the result of predation attempts by groups of ants attempting to overpower and kill the tiger beetle, making the ants the predators and the tiger beetles the prey.

Note ant head attached by its mandibles to the base of the tiger beetle's left maxillary palpus.

Although some ants are well known for their predatory horde behavior, I’m not sure I buy this as an explanation for the common occurrence of ant heads attached to tiger beetles.  Tiger beetles themselves often prey on ants, and while I have seen numerous tiger beetles with ant heads attached to them, I have never seen one actually being overpowered by ants (scavenging an already dead tiger beetle, yes—but not overpowering and killing one).  Moreover, the ant heads are nearly always attached to the base of an antenna or palpus—right next to the tiger beetle’s mouth, and almost never on more distal parts of the antennae or other parts of the body.  If the ants were attempting to prey on the tiger beetle, wouldn’t they also (if not even more commonly) be found attached to the tiger beetle’s legs or soft intersegmental membranes?  And how would the ants have come to be decapitated while in the act of attempting to overpower the beetle?  I suggest it is more likely that the ants were prey, latching onto the nearest part of their killer’s body in a last ditch attempt to avoid their inevitable fate.  The antennal and palpal base are about the only tiger beetle body parts that would be within reach of an ant in a tiger beetle’s toothy grasp.  While the rest of the ant was consumed, the head remained because it was firmly attached to the beetle.

I realize that an identification based only on the detached head of an ant may be difficult, but if one is possible it would be appreciated.  The ant head shown in Pearson and Vogler (2001) was identified as Polyergus sp.

REFERENCES:

Pearson, D. L., C. B. Knisley and C. J. Kazilek. 2006. A Field Guide to the Tiger Beetles of the United States and Canada. Oxford University Press, New York, 227 pp.

Pearson, D. L. and A. P. Vogler.  2001. Tiger Beetles: The Evolution, Ecology, and Diversity of the Cicindelids.  Cornell University Press, Ithaca, New York, 333 pp.

Copyright © Ted C. MacRae 2011

Predator Satiation

Polistes carolina/perplexus with Magicicada prey | Shaw Nature Reserve, Missouri

I’ve probably used the term predator satiation more often during the past couple of weeks than I have during the entire rest of my life.  Students of ecology know this as an antipredator adaptation in which prey occur at such high population densities that they overwhelm predator populations.¹  This ‘safety in numbers’ strategy reduces the probability that any given individual will be consumed, thereby ensuring that enough individuals survive to reproduce.  With St. Louis currently experiencing the appearance of Brood XIX of periodical cicadas, I’ve gotten lots of questions recently from many coworkers and friends wanting to know more about these cicadas.   Often the first question is “What is their purpose?”  My standard reply begins with a statement that they, like all living organisms, are the products of natural selection, which then presents an opportunity to explain how natural selection might result in such massive, temporally synchronized, multiple-species populations.  A few eyes have glazed over, but I think most have found my answer interesting, often even leading to further questions about where they lay their eggs, what is their life cycle, why are they so loud, how do they “do it” and select mates, etc.  Of course, as an entomologist with a strong natural history orientation, I’m always anxious to introduce people to ecological concepts, and right now the periodical cicada is providing a conspicuous, real-life example of such.

¹ Also called “predator saturation,” although this term might be misconstrued to mean that it is the predators that are over-abundant.

First the eyes...

A few weeks ago, right at the beginning of their emergence in the St. Louis area, my friend Rich Thoma and I observed predator satiation in action.  While hiking one of the trails at Shaw Nature Reserve, we heard the unmistakable shriek and cellophane-sounding wing flapping of a just-captured male cicada.  Tussling on the ground ahead of us was the cicada in the grasp of a Polistes carolina/perplexus wasp, which was repeatedly stinging the hapless cicada on the underside of the abdomen.  The shrieking and wing-flapping grew less frequent as the stinging continued, until at last the cicada lay quiet.  As we approached, the wasp spooked and flew off, but we knew it would be back—we parked ourselves in place while I setup the camera, and before long the wasp returned.  It took several minutes of searching from the air and on the ground before the wasp finally relocated her prey, but once she did she began voraciously devouring it.  As the wasp was searching, we hypothesized that our presence had altered the visual cues she had memorized when flying off, resulting in some confusion when she returned, and thus the long period of time required to relocate her prey.

...then the legs!

We watched for awhile—first the eyes were consumed, then the legs.  As it consumed its prey, Rich remarked that he bet he could pick up the wasp and not get stung—likely the entirety of its venom load had been pumped into the cicada.  Both of us declined to test his hypothesis.  We also wondered if the wasp would butcher the cicada after consuming part of it and bring the remaining pieces back to the nest.  We had seen a European hornet do this once with a band-winged grasshopper, consuming the head, then cutting off the legs from the thorax and flying away with it before returning to collect the abdomen as well.  No butchering took place this time, however, the wasp seemed content to continue eating as much of the cicada as possible—a satiated predator if there ever was one!

Leg after leg is consumed.

One eye and all six legs down, time to start on the abdomen.

Copyright © Ted C. MacRae 2011

Sawfly larva – Periclista sp.

As I was photographing spring coralroot orchids in my front yard, I noticed a small green object clinging to the underside of one of the flowers.  Zooming in with the camera lens revealed the object to be a caterpillar, but this was no ordinary caterpillar (i.e., a member of the order Lepidoptera), but rather a sawfly larva.  Sawflies are not lepidopterans, but members of the order Hymenoptera, making them more related to bees and wasps while their larvae look much more like those of a moth or butterfly.  Although there are few absolutes in the world of insects, distinguishing sawfly larvae from lepidopteran caterpillars is as easy as counting the prolegs (false legs behind the three pairs of true legs)—lepidopterans have at most 5 pairs of prolegs (often less), while sawfly larvae always have 6 or more pairs of prolegs.

While its identity as some type of sawfly was immediately apparent, I wasn’t sure beyond that.  One thing I was fairly certain about was that the orchid itself was likely not its host plant.  I could see no evidence of feeding on any part of the plant on which it was resting (and orchids by the large seem relatively free of defoliating insect pests), nor could I find any other sawfly larvae on the plant or its neighbors (where there is one sawfly larva, there are usually more).  Rather, I suspected that it had fallen from one of the many native oaks and hickories that shade the front yard (and which provide the habitat that allows orchids to grow in my front yard to begin with).  Nevertheless, I Googled “orchid sawfly,” only to come up with page after page of links referring to the sawfly orchid (Ophrys tenthredinifera), native to the Mediterranean Region.  That wasn’t much help, so I began the process of slogging through the sawfly images posted at BugGuide in hopes that something close had already been posted.  Eventually I stumbled upon photos of larvae in the family Tenthredinidae, subfamily Blennocampinae that exhibited similar branched dorsal spines (including the pestiferous Monophadnoides rubi, or raspberry sawfly).  I gradually settled on a generic ID of Periclista sp. based on the resemblance of the larva in my photos to those in photos such as this one, and the fact that this genus of ~20 North American species feeds as larvae on oak and hickory seems to support to the identification.

This past week’s Super Crop Challenge was taken from the dorsal side of the caterpillar in the first photo and rotated—it apparently proved a little too tough for most people to handle.  Predictably, most participants guessed one of the different spined caterpillars of the order Lepidoptera, but Dave used the extended quiz time wisely and eventually came up with a correct ID and the challenge win.  He even suggests the species P. marginicollis, based on its widespread eastern distribution and the bifurcate processes—it’s a good guess, but the larval description in Smith (1969) is a little beyond my comprehension, so I’m leaving the ID at Periclista sp.  Dave’s win moves him into the top spot in the current overall standings, while Tim moves up to tie Alex for 2nd place with 9 pts each.

REFERENCE:

Smith, D. R.  1969.  Nearctic sawflies I.  Blennocampinae: Adults and larvae (Hymenoptera: Tenthredinidae).  U.S. Department of Agriculture, Agricultural Research Service, Technical Bulletin No. 1397, 179 pp. + 19 plates.

Copyright © Ted C. MacRae 2011