Not long ago, I received an interesting series of photographs from Joe Warfel, a nature photographer and macro specialist based in Massachussetts. Joe traveled to Arizona last July, where he photographed an aggregation of Cicindela (Cicindelidia) sedecimpuntata (Western Red-bellied Tiger Beetle¹) near a small pool in the bottom of a dry creek bed at night. Joe estimates that there may have been as many as 200 to 300 beetles per square meter in the aggregation, most of which were just “hanging out” and with only occasional individuals mating or feeding on moths that had been attracted to his headlamps.
¹ Found in the Sonoran and Chihuahuan Deserts of the southwestern U.S. and south through Mexico to Costa Rica. U.S. and northern Mexican populations are assigned to the nominate subspecies, while more southern populations are classified into four additional subspecies (Erwin and Pearson 2008).
Western Red-bellied Tiger Beetles are among the first tiger beetles to appear prior to the summer monsoons in the Sonoran Desert. The species is famous for its daytime aggregations of as many as several thousand individuals, which congregate along the drying waterways and prey upon stranded tadpoles and other aquatic organisms (Pearson et al. 2006). Joe noted that he has seen these aggregations many times before during the daytime at small pools and mudflats, with beetles usually mating and feeding frantically. However, the aggregation shown in these photographs differs from those daytime aggregations by the relative inactivity of the beetles and the fact that they were congregated on dry ground rather than the moist areas that they frequent during the daytime. In these respects, it seems to more resemble a communal nocturnal roost such as has been reported for several species of Odontocheila in South America. In those cases, up to 70 beetles have been found resting on the foliage of low shrubs, apparently as an adaptation to avoid predation by multiplying chemical defense effectiveness as well as awareness of approaching enemies (Pearson and Vogler 2001 and references therein). Cicindela sedecimpunctata is primarily a diurnal species (i.e., it is active during the daytime), though individuals are often attracted to lights at night, and adults of most diurnal species have been reported spending the night protected in burrows or under detritus and vegetation. I am not aware of communal nocturnal roosts as a reported behavior for C. sedecimpunctata or any other North American tiger beetle species.
It is a bit ironic to think of tiger beetles – voracious predators that they are – as prey, but they must have many of their own predators to deal with since most species employ multiple antipredator mechanisms. In addition to the communal roosting behavior seen in these photos, a second antipredator characteristic exhibited by this species can be seen in their bright orange abdomen. The abdomen is fully exposed only during flight, seemingly implying a “flash coloration” function for the bright color that disappears upon landing, momentarily confusing potential predators. However, Pearson (1985) experimentally determined that orange abdomens in tiger beetles actually have an aposematic function in protecting them from predation against robber flies. Most tiger beetle species with an orange abdomen also release a combination of benzaldehyde and cyanide² when captured (any tiger beetle collector is familiar with the characteristic “fruity” smell of a tiger beetle releasing benzaldehyde). Pearson painted the abdomen of paper tiger beetles models either orange or black and endowed them with or without a drop of fresh benzaldehyde. When presented on a tether to robber flies in the field, orange-abdomened models with benzaldehyde triggered significantly fewer attacks from robber flies than any other combination. Interestingly however, vertebrate predators (lizards and birds) were not deterred by the defense chemicals or by the orange abdomen, perhaps explaining why only some and not all tiger beetle species produce defense chemicals and have bright orange abdomens (Pearson and Vogler 2001).
² Tiger beetles, thus, join millipedes as being among the few invertebrates that are capable of producing cyanide.
My sincere thanks to Joe Warfel for allowing me to use his photographs. More of his work can be seen at Eighth-Eye Photography. Joe also recently had several images published in American Scientist magazine (November/December 2009 issue) for an article on harvestmen. Check out the jaws on that juvenile!
REFERENCES:
Erwin, T. L. and D. L. Pearson. 2008. A Treatise on the Western Hemisphere Caraboidea (Coleoptera). Their classification, distributions, and ways of life. Volume II (Carabidae–Nebriiformes 2–Cicindelitae). Pensoft Series Faunistica 84. Pensoft Publishers, Sofia, 400 pp.
Pearson, D. L. 1985. The function of multiple anti-predator mechanisms in adult tiger beetles (Coleoptera: Cicindelidae). Ecological Entomology 10:65–72.
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 2010
Beetles In The Bush 
Interesting article. I’m curious if tiger beetles will prey on each other during these aggregation events, or at any other time?
I couldn’t find any references to such, and I don’t get the impression that it is very common. Attacking another individual of the same species is actually a risky proposition for a predator, as the opposition is equally strong and well-armed. There would have to be quite a payoff to favor that kind of behavior.
Of course, I have seen it in individuals that I’ve kept in an aquarium, but in such a confined space without regular access to prey I don’t find that surprising.
I have witnessed T. virginica and T. carolina eat C. cupracens and C. repanda. The big guys like to eat the little guys. I had a Tiger Beetle aquarium set up last summer. It was fun to watch them. I’m pretty sure that that cupracens ate each other as well but I can’t clearly recall that. The all pretty much left C. punctulata alone untill he was about the last one left in the tank.
I think interspecific predation is much more common than intraspecific predation – and especially in a terrarium setting as I’ve noted above. It’s rather common for bigger species to kill smaller species that occupy the same habitat, but I think this is more for competetive exclusion than simple predation, as even a smaller tiger beetle species is a formidable opponent compared to normal prey items and presents a great risk to the aggressor.
Interesting that punctulata were the last to be eaten – they are the only species of those you mention that utilize benzaldehyde/cyanide defense chemicals.
I think ‘intraguild predation’ would be how some ecologists would label this type of predation. Although I have published on the phenomenon, and it is fun to test in the lab in a Cloudsley-Thompson sort of way (e.g. Galeodes vs scorpion), I’ve always been a bit skeptical that it goes beyond the usual ‘if you meet it, try to eat it’. You’d have to show that a tiger beetle sought out its competitors for dinner or attacked them at a higher rate than non-predatory prey of a simiar size. Of course, given that tiger beetles like sunny days, that could be a very nice field project.
“Galeodes vs scorpion” – that would be great!
Hoback and colleagues presented some evidence for this among tiger beetles in Nebraska’s resource-poor saline flat habitats, finding that Eunotat togata (a smaller species) not only serves as prey for Habroscelimorpha circumpicta (a larger species), but also that E. togata was less efficient at capturing prey in the presence of H. circumpicta. I guess you don’t actually have to kill and eat your competitor to exclude them from resources.
Great read, Ted.
Didn’t know that certain Cicindela could produce cyanide, but I did know about the millipedes.
Perhaps – for the sake of science of course – someone could mimic the lemur in this youtube vid, but with a few beetles and report back? Any volunteers? 🙂
That’s a pretty funny video – I couldn’t tell if the lemurs were drooling from drunken delight or toxic stupor!
Living in the Sonoran desert, I’m definitely going to keep an eye out for these beetles.
There are a whole bunch of other tiger beetle species in your neck of the woods, er… desert! July/August is their season.
Great photos. I was at the same conference with Joe when he went out and got that photo- however I was not with him when he found the aggregation. C. sedecimpunctata was incredibly abundant in southeast Arizona last summer.
Hi Doug – I’ve collected it a few times before on my previous trips to Arizona (before really having any focus on the group). I’d love to see some of these aggregations for myself sometime.
I so need to get back to Arizona!
I mouthed, “No WAY!” when I saw that first picture. I’m a newbie to insects in general, and have yet to see my first Tiger Beetle in person – so this aggregation thing came as a complete surprise. How very cool. Cyanide emissions? Cyanide smells fruity? I always learn things when I drop by, Ted. 🙂
Hi Amber – glad you like it. Of course, I’ve yet to see an aggregation like that myself (but it’s just a matter of time).
btw, it’s the benzaldehyde in the cyanide/benzaldehyde mixture they emit that smells fruity – I’m sure the cyanide has a decidedly “different” smell 🙂
I’ve witnessed similar aggregations of this species around creeks and standing water in southern New Mexico.
Are you talking about the daytime aggregations (for which this species is well-known) or the nighttime aggregations shown here?
I witnessed a daytime aggregation of this species last July at a muddy roadside pool in the Santa Rita
Mtns., Arizona. I didn’t see the site at night, so don’t know if they were aggregating at night as well.
Charlie S.