Predator or Prey?

August 15, 2011October 10, 2011 / Ted C. MacRae / 25 Comments

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.

Predator Satiation

June 13, 2011October 10, 2011 / Ted C. MacRae / 25 Comments

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.

Orange-banded checkered beetle

April 22, 2010October 10, 2011 / Ted C. MacRae / 17 Comments

As a student of woodboring beetles for more than a quarter-century now, I’ve had occasion to encounter a goodly number of checkered beetles (family Cleridae) – both in the field and as a result of rearing them from dead wood. Checkered beetles are not as commonly encountered as other woodboring beetle families such as Buprestidae and Cerambycidae, and they also generally lack the size, diversity, and popularity with coleopterists that those aforementioned beetle families enjoy. However, despite these shortcomings as a group, checkered beetles are among the most brightly colored and boldly patterned of beetles. Unlike the beetles with which they often found, checkered beetles are not actually themselves woodboring beetles, but rather predators of such (particularly bark beetles in the weevil subfamily Scolytinae).

This particular species, Enoclerus ichneumoneus, is one of the more conspicuous members of the family in eastern North America. Although the genus to which it belongs is the largest of the family (32 species in North America north of Mexico), the wide orange band across the middle of the elytra and elongate scutellum make this species distinctive and unlikely to be confused with any other. I found this individual along the Ozark Trail in southern Missouri on a recently fallen mockernut hickory (Carya alba) – a number of other adult buprestid and cerambycid species were also found on this tree, all of which were mating, searching for mates, or laying eggs within the cracks and fissures on this new-found resource. In the past I have encountered large numbers of adults of this species on dead willow (Salix caroliniana) from which I later reared an even larger number of a small willow-associated buprestid, Anthaxia viridicornis. Whether the buprestid larvae served as prey for E. ichneumoneus is difficult to say, but no other potential prey beetle species were reared from the wood.

The bright, distinctive colors exhibited by many checkered beetles might seem to suggest aposematic, or warning, coloration to discourage predation; however, the question of checkered beetle palatability to predators has not been adequately studied (Mawdsley 1994). The colors and patterns of many species, especially in the genus Enoclerus, seem to mimic species of velvet ants (family Mutillidae) and true ants, but other beetles (e.g. species of Chrysomelidae and Tenebrionidae) and even flies have also been suggested as models. Still other checkered beetle species seem to be more cryptically than mimetically marked, and there are several tribes whose members seem to be chiefly nocturnal and are thus mostly somber-colored.

Of the 37 genera occurring in North America north of Mexico, I have in my collection representatives of more than 100 species in 23 of those genera. The majority of that material has been reared from dead wood collected for rearing Buprestidae and Cerambycidae – much of it coming from Texas and Arizona as well as here in Missouri.

Photo Details: Canon 100mm macro lens on Canon 50D, ISO 100, 1/250 sec, f/14, MT-24EX flash 1/4 power w/ Sto-Fen diffusers, photo lightly cropped.

REFERENCE:

Mawdsley, J. R. 1994. Mimicry in Cleridae (Coleoptera). The Coleopterists Bulletin 48(2):115-125.

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Assassin ate

September 21, 2009October 10, 2011 / Ted C. MacRae / 20 Comments

I came upon this interesting scene last month while hiking through Allen David Broussard Catfish Creek Preserve State Park, which preserves some of the highest quality remnants of sand scrub habitat on the Lake Wales Ridge of central Florida. The spider seems to be Peucetia viridans (green lynx spider), widespread across the southern U.S. and distinguished by its bright transparent green color with red spots and black spines (Emerton 1961). These largest of North American lynx spiders hunt diurnally on low shrubs with an agility excelled only by the jumping spiders (Salticidae) and aggressively attack their insect prey. In this case, the prey is one of the so-called “bee assassins” of the genus Apiomerus (Hemiptera: Reduviidae). The common and generic names of these insects both derive from their habit of preying upon bees, not only on flowers but also by ambushing them at nest entrances, although other insects are preyed upon as well. Ironically, this particular assassin himself got ate.

An interesting situation was uncovered while I tried to determine which species of Apiomerus was represented by the prey. By virtue of its pale ventrals with the front and hind margins black, it keys to A. spissipes in a literature-based key to Florida Reduviidae (Bierle et al. 2002) – one of two species considered widely distributed across the eastern U.S. In reality, however, it appears that this individual represents another species named almost 30 years ago but which remains officially undescribed. As explained in this BugGuide post by Daniel Swanson, the genus was revised by Berkeley grad student Sigurd Leopold Szerlip in partial fulfillment of the requirements for a Ph.D., who proposed a number of taxonomic acts including the description of 19 new species. Among these were eastern U.S. populations to which the name A. spissipes had been applied, with those in Florida being described as the new species “A. floridensis“. However, dissertations do not meet the criteria of publication according to Article 8 of the International Code of Zoological Nomenclature (ICZN 1999), and none of the dissertation was formally published. Thus, “A. floridensis” remains an invalid, unpublished name. This is a most unfortunate situation, as Swanson considers the dissertation to be well done. It is not only names, but important information about life histories and detailed genitalic studies that remain unavailable to the scientific community as well. What are the nomenclatural impacts of this work remaining unpublished? Is this as much a failure by the advising professor as by Szerlip himself? What ethical considerations would need to be addressed in order for it to be published in absentia, or is this even possible?

Photo details: Canon 100mm macro lens on Canon EOS 50D (manual mode), ISO-100, 1/250 sec, f/13, MT-24EX flash 1/2 power through diffuser caps.

REFERENCES:

Bierle, S., E. Dunn, S. Frederick, S. Garrett, J. Harbison, D. Hoel, B. Ley and S. Weihman. 2002. A literature-based key to Reduviidae (Heteroptera) of Florida (assassin bugs, and thread-legged bugs). Unpublished manuscript, University of Florida, Department of Entomology and Nematolgy, Insect Classification ENY 4161/6166, 18 pp.

Emerton, J. H. 1961. The Common Spiders of the United States. Dover Publications, Inc., N.Y., xx + 227 pp.

International Commission on Zoological Nomenclature [ICZN]. 1999. International Code of Zoological Nomenclature, 4th Edition. The International Trust for Zoological Nomenclature, c/o Natural History Museum, London. xxix + 306 pp.

Szerlip, S. L. 1980. Biosystematic revision of the genus Apiomerus (Hemiptera: Reduviidae) in North and Central America. Unpublished Ph.D. thesis, University of California, Berkley, CA.

Prey bee mine

September 14, 2009October 10, 2011 / Ted C. MacRae / 12 Comments

Promachus hinei preying upon a small carpenter bee

Robber flies of the genus Promachus – the so-called “giant robber flies” – are among the more conspicuous and fearless predators seen in Missouri’s glades. Able to capture almost any flying insect regardless of size, this individual – seen at Long Bald Glade Natural Area in Caney Mountain Conservation Area – was found snacking on what, according to my hymenopterist friend Mike Arduser, appears to be a female individual of the genus Ceratina (the so-called small carpenter bees in the family Apidae). Of the three “tiger-striped” (referring to the yellow and black striping of the abdomen) species of Promachus in the eastern U.S. species, P. hinei is the most common in Missouri. It is distinguished from the more southeastern P. rufipes by its reddish versus black femora and from the more northern P. vertebratus by the larger dark areas dorsally on the abdominal segments and distinctly contrasting two-toned legs. Despite their common name and impressive size, however, they are not the largest robber flies that can be seen in these glades…

Photo details: Canon 100mm macro lens on Canon EOS 50D (manual mode), ISO-100, 1/250 sec, f/13, MT-24EX flash 1/4 power through diffuser caps.

Tiger Beetle Rearing

May 20, 2009October 10, 2011 / Ted C. MacRae / 35 Comments

I recently found an interesting website called Tiger Beetle Rearing. This website by doctoral candidate Rodger Gwiazdowski in the Joseph S. Elkinton lab, University of Massachusetts, Amherst contains a wealth of information and photographs covering equipment, techniques, and methods for rearing tiger beetles from egg to adult, with a primary focus on rearing endangered and threatened species of tiger beetles for conservation and re-release into the wild. The lab has reared a number of tiger beetle species but is particularly interested in the Puritan tiger beetle (Cicindela puritana), threatened in the northeastern U.S. After the first year of rearing, 90 2nd and 3rd instar C. puritana larvae were obtained and, as of the last update, were overwintering in individual tubes. You’ll need to register with the site with a username and password to access the site, but this is accomplished quickly and easily.

Welcome to the Hotel Cicindela!

I found this website of great interest as I begin my own efforts at rearing these beetles in the laboratory. My primary interest is in rearing larvae that I collect in the field to adulthood – adults are much more easily identified than larvae (indeed, the larvae of many species remain undescribed), and rearing field-collected larvae is one way to get around the often limited temporal occurrence that many tiger beetle species exhibit as adults. My operation isn’t nearly as sophisticated as the one developed in the Elkinton lab, but then I’m just a working stiff trying to do this (and a million other things) on the side. Despite this, I have had my first success, rearing to adulthood a larva I collected during the summer last year (see my post It’s a girl!). In addition, I currently have a number of larvae collected last fall in Nebraska and South Dakota, which I put in terraria of native soil and kept in a cold incubator during the winter. I pulled them out earlier this spring, and soon afterwards a number of larvae opened up their burrows and have been feasting on fall armyworm and corn earworm caterpillars every 2-3 days or so. The larvae were collected from a variety of habitats and soil types, including sand, alkaline seeps, and red clay banks, so I’m hopeful that the ensuing adults will represent a variety of interesting species – perhaps some that I did not encounter in the field during that trip.

Beyond this, however, I am also interested in trying my hand at cross-breeding experiments – particularly with Missouri’s unique population of Cicindela scutellaris (festive tiger beetle). I’ll need to wait until fall for this, however, since adults that are active in the field right now are sexually mature and have presumably already mated. In the fall, a new generation of sexually-immature adults will emerge and feed for a time before burrowing back in for the winter and re-emerging the following spring ready to mate. I would like to cross individuals from southeastern Missouri – representing an intergrade between the northern subspecies lecontei and the southern subspecies unicolor – with individuals from the northern part of the state that are clearly assignable to subspecies lecontei. If possible, I would also like to obtain individuals from even further south that are clearly assignable to subspecies unicolor and cross them with both the southern and northern Missouri populations. These crossing experiments may provide some insight into which of the subspecies the intergrade population is more closely related to, and it will be interesting to see how closely the progeny from the lecontei x unicolor cross resemble individuals from the intergrade population and the range of variation that they exhibit. I should mention that Matt Brust (Chadron State College, Nebraska) has done a number of these inter-subspecific crosses with C. scutellaris, with some very interesting results among the progeny.

What I can do right now is work on techniques to make sure I can get females to lay eggs and then rear the larvae all the way through to adulthood. For this, I brought back 9-10 live individuals from two localities of the intergrade population encountered on my recent trip to the southeastern lowlands. I put equal numbers of males and females from each locality into separate terraria – each filled with native soil and a hydrophilic polymer gel made of anionic polyacrylamide. The beetles, who normally obtain moisture from their food or by “chewing” moist soil, chew instead on the gel. This eliminates the need to maintain a water dish or cotton batting that must be changed daily in order to prevent the growth of mold and bacteria. A few of the adults in each terrarium died shortly afterwards, possibly a result of stress or dehydration during transport (the photo right shows how eagerly they imbibed moisture from the polymer gel after being placed in the terrarium), but the remainder have lived for four weeks now and have been digging burrows and feeding whenever food is offered. According to Matt Brust, C. scutellaris does not lay eggs on the surface of the soil (as does C. celeripes), but rather lays them about 1.5 to 2 inches below the surface. It takes 2-3 weeks before the eggs start hatching, so I am expecting to see larval burrows appearing anytime now. Matt tells me the key to getting eggs is to feed the adults “big-time” – thus, I have been offering fat, juicy fall armyworm or corn earworm larvae to the adults whenever they are out of their burrows. Watch this entertaining video of one adult having lunch:

Bon appétit!

April 30, 2009October 10, 2011 / Ted C. MacRae / 8 Comments

I collected this larva in northwest Nebraska during last year’s Fall Tiger Beetle Trip. I collected an adult Cicindela lengi (blowout tiger beetle) at the spot – a species that greatly resembles but is much less common than the ubiquitous C. formosa (big sand tiger beetle – see my post Cicindela lengi vs. Cicindela formosa for a comparison of the two species). Before finally finding that adult, however, I had fished out several larvae from the site in the hopes that they represented that uncommon species (see how I did this in my post Goin’ fishin’). After collecting the larvae and placing them in a small terrarium with native sandy soil, they burrowed in but then closed up shop – I wasn’t sure whether they had survived or not. In early December I put the terrarium in a 10°C incubator for the winter and brought it back out earlier this month. Yesterday, happily, this larva and one other opened up their burrows again, so with any luck I’ll feed them well and they’ll complete their development. While I do hope they represent C. lengi, other possibilities include C. scutellaris (festive tiger beetle), which would not be exciting, and C. nebraskana (prairie long-lipped tiger beetle), which would be VERY exciting. One species I do not have to worry about it being is C. formosa, as the larvae of that species make very unique excavations in the sand with the burrow opening directed towards the excavation (I don’t believe I’ve posted photos of that here, yet – I’ll have to do so soon).

In the meantime, here is a closeup of the larva in the video prior to feeding. Those of you who have ever reared or photographed tiger beetle larvae will know just how easily “spooked” these larvae can be – any sudden movement will cause the larva to “drop” into its burrow and sit there for awhile. As a result, it was a real challenge to go through the whole process of taking first the photos and then the video while feeding it without causing it to drop.

Coming soon – lunchtime for adults!

Millipede assassin bug

February 18, 2009October 10, 2011 / Ted C. MacRae / 18 Comments

I continue the hemipteran theme begun in the last post with this photograph I took in South Africa below the Waterberg Range in Northern (now Limpopo) Province. I recognized them as members of the family Reduviidae (assassin bugs), and since to my knowledge species in this family are exclusively predaceous (except for the so-called “kissing bugs” of the mostly Neotropical subfamily Triatominae, large distinctive bugs that feed exclusively on vertebrate blood), I found what I took to be a case of scavenging on a dead millipede to be rather curious. It had rained the previous evening, resulting in a burst of millipede (and insect) activity that night, and this scene was rather commonly encountered the following morning. Of course, appearances can be deceiving, and it turns out that I actually was witnessing predation – and a most unusual case at that. The individuals in this photo represent Ectrichodia crux (millipede assassin bug), a common species in many parts of southern Africa. Although nearly 500 species of assassin bugs are known from the region (Reavell 2000), E. crux is easily recognizable due to its large size (adults measure up to 22 mm in length), stout form, and coloration – shiny black, with a distinctive black cross incised on its dull yellow thorax and with yellow abdominal margins (Picker et al. 2002). The nymphs as well are distinctive – bright red with black wing pads. Clearly, these insects are advertising something.

Ectrichodia crux belongs to the subfamily Ectrichodiinae, noted for their aposematic coloration – often red or yellow and black or metallic blue, and as specialist predators of Diplopoda (Heteropteran Systematics Lab @ UCR). Species in this subfamily are most commonly found in leaf litter, hiding during the day under stones or amongst debris and leaving their shelters at night in search of millipedes (Scholtz and Holm 1985). They are ambush predators that slowly approach their prey before quickly grabbing the millipede and piercing the body with their proboscis, or “beak.” Saliva containing paralytic toxins and cytolytic enzymes is injected into the body of the millipede to subdue the prey and initiate digestion of the body contents, which are then imbibed by the gregariously feeding assassin bugs.

Millipedes employ powerful chemical defenses – primarily benzoquinones and sometimes hydrogen cyanide gas as well, which are discharged from specialized glands along the millipede’s body – to protect themselves from predation. Thus, specialized predation of millipedes is a niche that has been exploited by relatively few predators, and little is known about the mechanisms used for circumventing these defenses. The recently reported millipede specialist, Deltochilum valgum (order Coleoptera, family Scarabaeidae), has been observed killing its prey by violently decapitating and disarticulating it before feeding on the body contents (Larsen et al. 2009, summary here); however, the exact manner by which the beetle avoids or withstands the millipede’s chemical discharges remains unknown. For ambush predators such as Ectrichodia crux and other ectrichodiines, a strategy similar to that described for another millipede specialist predator, larvae of the phengodid beetle, Phengodes laticollis (order Coleoptera, family Phengodidae), might be employed. This species subdues its millipede prey by piercing thinner regions of the millipede’s integument (e.g., intersegmental membranes on the ventral surface) with its hollow sickle-shaped mandibles and apparently injecting gastric fluids that abruptly paralyze the millipede, thereby preventing it from discharging its gland contents (Eisner et al. 1998). These undischarged benzoquinones remain confined to the glands and are prevented from diffusing into the body cavity by the glands’ impervious cuticular lining, thus allowing the phengodid larva to safely imbibe the liquified systemic contents of the immobilized millipede.

REFERENCES:

Eisner, T., M. Eisner, A. B. Attygalle, M. Deyrup and J. Meinwald. 1998. Rendering the inedible edible: Circumvention of a millipede’s chemical defense by a predaceous beetle larva (Phengodidae). Proceedings of the National Academy of Sciences USA 95(3):1108–1113.

Larsen, T. H., A. Lopera, A. Forsyth and F. Génier. 2009. From coprophagy to predation: a dung beetle that kills millipedes. Biology Letters DOI:10.1098/rsbl.2008.0654.

Picker, M., C. Griffiths and A. Weaving. 2002. Field Guide to Insects of South Africa. Struik Publishers, Cape Town, 444 pp.

Reavell, P. E. 2000. The assassinbugs (Hemiptera: Reduviidae) of South Africa. http://oldwww.ru.ac.za/academic/departments/zooento/Martin/reduviidae.html#ectrichodiinae.

Scholtz, C. H. and E. Holm (eds.). 1985. Insects of Southern Africa. Butterworths, Durbin, South Africa, 502 pp.

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Beetles In The Bush

Experiences and reflections of a Missouri entomologist

predation

Predator or Prey?

Predator Satiation

Orange-banded checkered beetle

Assassin ate

Prey bee mine

Tiger Beetle Rearing

Bon appétit!

Millipede assassin bug

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