Biodiversity Highlight - Series #2: Passalidae of the Bull Run Mountains

Biodiversity Highlight (Series #2): Horned Passalus Beetle (Odontotaenius disjunctus)
Virginia Outdoors Foundation - Bull Run Mountains Natural Area Preserve

Odontotaenius disjunctus (Horned Passalus Beetle) - A full life history of the species spotted within a rotting log on the Northern Section of The Preserve
© Michael J. W. Carr, some rights reserved (CC-BY-NC); (Larvae [Left], Pupa [Center], Adult [Right])

Hello again everyone,

Last week we completed our first biodiversity highlight series investigating the Lucanidae, or stag beetles found within the Bull Run Mountain Natural Area Preserve. This week we will be starting and completing our second highlight series while focusing on the Passalidae family! Luckily for this author, the Passalidae of our Mountain haven includes only one species - Odontotaenius disjunctus, or the bess beetle. This family deserves an early mention in our biodiversity series as it is one of the most charismatic and ubiquitous "big" beetles present within the Bull Run Mountains and the greater Northern Virginia Area. Odontotaenius disjunctus has many colloquial names including the horned passalus beetle, the patent leather beetle, the Betsy beetles, bess beetle, and even the Jerusalem beetle. Whatever you might call this curious insect, Odontotaenius disjunctus may be the best gateway beetle for the young and old. This can be chalked up to the species' overall docileness, slow movement, reluctance to fly, and charming stridulation. The species can be found throughout our area, including urban areas where decaying wood is available - yup, this week's mention is another saproxylic species (this may be a trend)!

My personal favorite colloquial name for this species is the bess beetle, which I will use for the rest of this article. It's also a ritual of mine to whisper "bess beetles are the best beetles" whenever I turn them up along a nature walk - whether they appreciate the recognition or not, no one will ever know, but I like to think it brings me luck in finding other interesting species while bugging.

The bess beetle is a remarkable model for some uncommon and interesting behavioral traits that are uncommon among Coleoptera. Most notably their colonial habits, their use of bioacoustic communication, and atypical display of brood care. These behaviors are somewhat disputed, but the species demonstrates pseudo-eusocial characteristics which are extraordinary among insects outside of Hymenoptera (think of our local Polistes [paper wasps] species), and Isoptera (termites). This ‘almost’ eusocial behavior can be viewed relatively easily when encountering a colony in the wild. Sprinkled across a thoroughly excavated fallen log you may find tens of beetles clumsily making their way into conspicuous cavities that branch and spread invisibly below the surface. This matrix of tunnels branches and terminates throughout the log supporting the entire lifecycle of the beetles. From egg to adult, the complete metamorphosis of the beetle takes place within the ever more broken down bosom of heartwood until the adults must disperse to find new host wood.

Odontotaenius disjunctus (Horned Passalus Beetle) - A mature and freshly molted adult pair observed in Richmond, Virginia

© Ashley McFad (@ashleymcfad), some rights reserved (CC-BY-NC)

The highlighting of this species so soon in our deep dive into Bull Run Mountains insect biodiversity isn’t without proper planning. As you may have recognized, this species of Coleoptera looks incredibly similar to some of our previously mentioned Lucanidae highlights. With the typical beetle-ish appearance, similar-looking clubbed antenna, and a pair of moderately large mandibles you would not be docked points for confusing the two. The families of Passalidae and Lucanidae are close relatives within the greater taxonomic classification. However, the nuance of coleopteran identification is on full display with our bess beetle. Let’s work through my description above: the typical beetle-ish appearance is actually distinguished by the bess beetles in their elongated form, deeply striated elytra, and shiny, raven-black coloration. This sets it apart from the somewhat similar looking Drocus sp. of Lucanidae. The clubbed antenna can prove to deceive when you aren’t familiar with the great variety of antenatal forms found in Coleoptera. The feature to note is that the bess beetle does not have a geniculate antenna, it doesn’t have an “elbow” and only curves with the intent of the beetle. Finally, those large mandibles, while mildly intimidating, are more robust and toothed in comparison with our local Lucanidae species.

Altogether, the bess beetle is a rather unique-looking beetle when you look more closely. The species does not display notable sexual dimorphism and only varies slightly in size among individuals.

Odontotaenius disjunctus (Horned Passalus Beetle) - Larval specimen observed in Maryland

© Dave (@djgphotographics), some rights reserved (CC-BY-NC)

Does the image above look familiar? If you saw our last post covering the “white grub” form of the Lucanidae it probably does! The bess beetle also has scarabaeiform larvae, but with a twist. In their larval form, the grubs of Lucanidae and Scarabiadae beetles can be difficult to tell apart, however, the larvae of the bess beetle have a unique morphology that can make a quick ID easy. At first glance, you might be able to tell the differences between the two types of larvae. The bess beetle larvae are a bit more elongated in appearance; more extended instead of coiled into themselves. The head of the bess beetle larvae also projects further away from the body than other white grubs. The biggest difference and the one which will help you get a positive ID within The Preserve is the lack of a third pair of developed legs. With only four legs the bess beetle larvae stand apart from its scarabaeiform larvae brethren. Interestingly, that final pair of legs is not absent in the larvae but has reduced into a peg-like form that acts as a sound-making apparatus. It is suspected that the stridulations of the larvae are used in signaling adult bess beetles to indicate hunger. Stridulation is not uncommon in larvae beetles, but its use of it in communication within a colonial setting is.

To take another side track off of the species itself, let’s quickly cover the process in all beetle utilizes to reach their best selves - complete metamorphosis or Holometabolous. Within the insect world, there are several forms of metamorphosis. These include little to no metamorphosis, or Ametabolous, where the insect develops without significant changes in its morphology. In this process of development, the adult form of the insect resembles a larger form of its juvenile shape (most prevalent in primitive insects like springtails and silverfish. Another metamorphic process is partial metamorphosis, or Hemimetabolous, where the life cycle of the insects consists of three developmental stages: egg, nymph, and adult. This process is like that of the cicada or grasshopper, where nymphs look similar to adults but lack wings and fully developed morphology. Finally, the final process of metamorphosis is what the sour bess beetle utilizes as a developmental life strategy - complete metamorphosis. This process is also utilized by Diptera (flies) and Lepidoptera (butterflies and moths) where the life cycle includes four stages: egg, larvae, pupa, and adult. In our banner image for this post, you can see the three life stages beyond the egg which the bess beetle passes through in its life cycle. A remarkable thing to see all at once when observing nature!

Thank you for reading! If you enjoyed this short article please leave a comment below to help us gauge community impact for our annual summary. Additionally, if you have any questions, comments, or corrections leave them below. While niche, this platform provides a unique opportunity for naturalists and enthusiasts to share their insights and stories regarding the amazing biodiversity that surrounds all of us.

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ABOUT #BullRunMountainsNaturalPreserve
The Bull Run Mountains are the easternmost mountains in Virginia. Virginia Outdoors Foundation - Bull Run Mountains Natural Area Preserve is approximately 2,350 acres that serve as a living laboratory that sits in the backyard of our nation’s capital. The preserve contains 10 different plant community types and a plethora of regionally uncommon and threatened plant and animal species. In 2002, this land was dedicated by the Virginia Department of Conservation and Recreation as a natural area preserve to protect the unique ecosystems found here. As the owner and manager of the preserve, the Virginia Outdoors Foundation is committed to protecting the special ecosystem found here and sharing it with the public through managed access.

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Posted on 17 de agosto de 2022 by mjwcarr mjwcarr



Publicado por saucierj hace 7 meses (Marca)

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