Species of Tragidion are among the larger and more attractive cerambycids in North America, making them popular among collectors. Their bright orange and black coloration clearly functions in mimicking spider wasps (family Pompilidae) in the genera Pepsis and Hemipepsis – the so-called “tarantula hawks.” Unfortunately, species of Tragidion have been difficult to identify due to a high degree of morphological similarity between species, wide range of variation across geographic areas within species, unusually high sexual dimorphism and dichromatism, and apparent potential for hybridization in areas of geographic overlap. This has confounded efforts to delimit species boundaries, resulting in a confusing assortment of names whose proper application has eluded even the most esteemed of North America’s cerambycid taxonomists. Recently, some much needed clarity was provided by Ian Swift and Ann M. Ray in the journal Zootaxa. Their taxonomic review of Tragidion – the first systematic treatment of the entire genus – recognizes seven species in North America and another four restricted to Mexico. Two species – T. agave from California and Baja California and T. deceptum from montane areas of the southwestern U.S. and northern Mexico (both pictured) – are described as new, and a third – T. densiventre from desert areas of the southwestern U.S. and northern Mexico – is raised from synonymy under T. auripenne. Four new synonymies are also proposed, and dorsal habitus photographs and a key to all species are provided. Life history information is limited for most species of Tragidion. One species – T. coquus – occurs broadly across the eastern and central U.S., where it breeds in a variety of dead hardwoods, especially oak. Several species occur in the southwestern U.S. and northern Mexico – some are found in xeric lowland desert habitats, where they breed in dead branches of Prosopis glandulosa and Acacia greggii (T. densiventre) or dead flower stalks of Yucca and Agave (T. agave and T. armatum), while a fourth (T. deceptum) is found in more montane habitats mining the heartwood of recently dead branches of Quercus. Adults of another species in California and Baja California, T. annulatum, are strongly attracted to brushfires and burning vegetation, and individuals have been observed landing on still-burning and smoldering shrubs, causing their legs and abdomens to melt to the surface of the branches. At several post-burn sites, the melted bodies of this species were common on the charred branches of their hosts, and females have been observed ovipositing on woody shrubs that have been burned. This species likely plays an important role in the decomposition of burned woody material in coastal areas of California. The remaining U.S. species – T. auripenne – is known from only a handful of specimens collected in xeric habitats in the Four Corners region of the southwestern U.S. It’s life history, as well as those of the four strictly Mexican species, remains essentially unknown.
REFERENCE: Swift, I., Ray, A. M. (2008). A review of the genus Tragidion Audinet-Serville, 1834 (Coleoptera: Cerambycidae: Cerambycinae: Trachyderini) Zootaxa, 1892, 1-25
10 thoughts on “New species and a review of the genus Tragidion”
Hi Ted, I’m very impressed! I’m kind of a naturalist/scientist myself, at heart! I’ll link you on my blog, I’m just really getting it up and going. Wow, your photography is awesome. Regards, Julie
Nice exposition of the genus. The only time I’ve encountered it was on the slopes of Kitt Peak. T. annulatus was relatively abundant taking sap from Baccharis. There were lots of Pepisi taking sap from the same shrubs. It was cool to see both model and mimic together.
Thanks, Julie – although I must point out that the photos in this particular post aren’t mine but were taken from the source I cited.
Doug – that was probably deceptum that you saw, as annulatum as now defined is restricted to California and Baja. I’ve also seen both deceptum and their Pepsis models sapsucking on Baccharis – yes, it’s alway cool seeing model/mimic pairs in the wild. The eastern U.S. species – coquus – has frustrated me for years. I’ve seen many in collections with label data suggesting attraction to rotten and fermenting fruit, but in all my years of collecting I’ve found a grand total of one!
I stand corrected! So I will say, your blog is awesome…..have a great week.
(I know you from the Bug Guide) so you think that all Tragidion from Santa Ritas and Catalinas in Arizona should be called T deceptum now? I’ll make changes in the BG then
Hi Margarethe. There are three species of Tragidion occurring in southeastern Arizona. Tragidion armatum and T. densiventre would be found more in lowland desert habitats, with the former utilizing Agave and Yucca (both Agavaceae) and the latter utilizing Acacia and Prosopis (both Fabaceae). Tragidion deceptum would be found in more montane habitats utilizing Quercus.
I found many in a mixed Oak Mesquite (Prosopis) area (Montosa Canyon St Ritas) others more in Mesquite Acacia grasslands in lower Madera Canyon. All were attracted to oozing Bacharis. They were considered T. annulatum before. I don’t know how to show a photo here, so this is my photo from BG. These are from Montosa Canyon http://bugguide.net/node/view/250737 so far I fail to see a difference to the ones from the lower area of Madera
For those who follow the link provided by Margarethe, those are Tragidion densiventre. I’ve corrected the photo above of T. deceptum that caused all the confusion, but I think it might be good if I provided additional clarification in a new post with photos comparing both species.
Ted, I have aTragidion out of Nolina parryi stalks from Nothing (there should be many more soon). It is a female and looks like T. agave as far as I can tell, but I don’t have access to the original paper. What do I need to see to tell? Interestingly enough, I did find a picture of the T. agave holotype on a website that says it was collected on the “7-level hill” in CA – Barney Streit has been hounding me about checking out Nothing, AZ for several years (I’m now doing that…) because it reminds him of the “7-level hill” in CA! Thanks! Paul
Hi Paul. Send an email to author Ian Swift – I’m sure he’d be glad to send you a reprint.