Notes on Passalid Beetles

These are one of my favorite beetles. Passalids, or bessbugs, are fairly common throughout the eastern U.S. They are a relatively large beetle, dark black with a hard shell, with gold "fringe." They stridulate when held, but don't attempt to bite. I've kept specimens from Louisiana, South Carolina, and Kentucky, but have had some problems keeping them for long periods of time. I had thought that mites (always present on the beetles) might have been the problem, but I was recently told otherwise. Al, from Texas A & M, is a passalid specialist, and gave me quite a bit of information on these interesting beetles. With Al's permission, I'm posting sections of his correspondance:


"There are two species of passalids known from the U.S. - Odontotaenius disjunctus (Illiger), from central Texas to Florida and north to very southern Canada; and Odontotaenius floridanus Schuster, from Florida. The latter was described only a few years ago, although it is a distinct and clearly valid species - it's just rare in collections. It will be interesting to work out how the two species coexist and partition their resources (dead wood) in the area of overlap. O. disjunctus is one of a very few species of passalids which have developed the ability to withstand freezing temperatures - which helps to explain its wide distribution. Most passalids are tropical; over 100 species are known from Mexico, for instance - about 15% of the described species in the family. Incidentally, the only known passalid fossil is from Oregon, suggesting serious climatic changes over the last 30 million years!

"Passalids are tropicopolitan, but not particularly vagile. They also occur in tropical Africa, India, Malay Peninsula, the Philippines and Australasia - outliers are in Jamaica, the Antilles, Cocos Id., Ceylon, southern Japan, southern Korea, south and west China, Palau, New Caledonia, Tasmania and Madagascar. They haven't reached some of the perfectly good islands in the Pacific. I'd guess that about 10% or more of the species are flightless, especially species on high mountains.

"Passalids are subsocial - the adults live in pairs, with both sexes sharing the tunnelling and family care duties. Eggs are laid in the galleries (and sometimes carried to a nest area in the mandibles of an adult), and the larvae are reared by the adults on finely-chewed wood chips mixed with feces. The larvae can not live long without the adults, unless they are at a very late stage of development. The adults assist the last stage larvae to build individual pupal chambers, possibly to protect them from hungry younger larvae, as well as predators. If a pupal chamber is damaged, not only the adults, but also older siblings (young adults, sometimes not yet fully sclerotized) of the pupa will repair it. The generations overlap - O. disjunctus adults can live for at least 14-16 months after reaching the adult stage. Some tropical species are suspected to live even longer.

"Both adults and larvae stridulate - by entirely different mechanisms. All known species possess this ability, suggesting that sound communication is very important to them - perhaps not surprising, since they live most of their lives in total darkness. The sounds used for aggression/defense are different from the courtship songs...and the courtship songs differ among species (not yet recorded for O. floridanus!).

"We assume that odors are also used to communicate, although this interesting area has not been studied - just a few field notes, suggesting that passalids can tell by the smell of the wood chips of a burrow whether the occupant is their same species and whether it is male or female. We have no idea which chemicals the beetles use to detect appropriately rotten logs, mates, competitors, predators, etc.

"If you live in the eastern U.S., you probably have passalids within a short drive (or walk!) - the same species as in LA, KY, SC. If you collect them now, they will probably be the young adults produced this last summer. This is one of the few beetles that you can find as adults at any time of the year!

"Jack Schuster has put out some general stuff on passalid sociality, behavior, etc., and is currently revising Odontotaenius. A lot of the general information and good stuff on individual species is in Spanish [articles by, co-authored by, or mentored by the current "Guru of Passalidology" (my term), Pedro Reyes Castillo]. Our genus is only one of about 60, worldwide, and is restricted to the New World, occurring mainly from Central America north."

Finding & Keeping Passalids

"Conifers tend not to be attractive - oak, elm, and a lot of other deciduous trees are acceptable. The trick is finding one of the proper age....then being able to reach the passalids. Jack uses a double-headed ax; I use a flat, curved wrecking bar - with the short, curved end sharpened, so that it gets a better bite in the wood. Old wood piles are good - the bottom layer, naturally. ;)

"You can easily keep a small group in a terrarium with little mortality, as long as they have sufficient moist, rotten wood. Indoor room temperature is probably fine - additional heat will be generated by the decaying wood/chips. Air exchange is important, as the beetles can be asphyxiated by the accumulation of the gases produced by the decaying wood (or their own respiration).

"Maintaining a reproducing colony is a <lot> tougher. Your best shot might be to keep them as pairs. with minimal disturbance (from people or other passalids), and where they can build a family burrow system. I rarely get egg-laying, and usually don't realize it until I empty a container to replace the "saw-dust" with new wood. My interests have been more towards recording courtship songs, rather than maintaining colonies. I suppose it might be possible to build a horizontal ant-farm-like container, but it would have to have both a dark cover, and a transparent cover beneath that - since passalids are <very> sensitive to air movement, perhaps even more so than to light. Selecting a pair is not a trivial matter, either - they are difficult to distinguish externally. Females <tend> to be a bit larger, and <tend> to be broader in proportion to their length than do males, but that doesn't work 100% of the time. I use a microscope to carefully, delicately check internally for a genital capsule (male), but the beetles are not at all cooperative, and can easily be damaged by a rough examiner. I have to use a heavy pair of gloves for some large tropical species, as their mandibles are definitely not present purely for decoration! If you find two passalids in a single tunnel system in the late spring or early summer, you could assume that they are a mated pair (especially if eggs or young larvae are present) - with a slight chance for error. ;)

"My wife and I recently returned from the Entomological Society of America meetings in Las Vegas. We manned one of two Texas A&M booths at the Insect Expo on the last day, and demonstrated parasitic wasps and passalids to constant clusters of the several thousand children that attended. They seemed to really enjoy holding the beetles - for some reason, our common U.S. species has a mental block against biting humans. I've been bitten (no blood) only once or twice in MANY hours of handling them - no such incident in Las Vegas from any of the 9 beetles over 4 intense hours. This does NOT hold for all passalids - some of the Central American species, including some tiny (1.5 -cm) ones will bite in a flash - junkyard dogs! The beetles also easily survive falls onto concrete.

"Incidentally - if one is placed on its back on a slick surface, it'll struggle and struggle, but I have never seen one open its elytra to right itself, as do most other beetles. Handy, if you need to keep them from running away, but close. If you find one that does use its elytra to flip over, please let me know!!!"

Passalids & Mites

"Passalids almost invariably have associated mites - several families of mites are found ONLY in association with passalids, and many genera and species are similarly restricted - suggesting a very long association between the two groups. I know of several graduate students who are interested in the co-evolution of these mites and their host passalids. Acarology students can beef up their collections significantly (at the family level) by checking passalids (and their galleries in rotting wood). I know of no mites that are harmful to the passalids, although there may well be some (e.g. tracheal inhabitants). Most of the mites are heavily sclerotized, dark- to medium-brown forms that run actively and freely over the outside ot the beetle, tending to spend more time on the underside, either just behind the head, or just behind the forelegs. The mites don't appear to be parasitic - their mouthparts are short, and the beetles are well-protected. I don't know of any benefit the beetle may receive, but the mites may live on secretions of the beetle, or just find protection from predators there while feeding off the decaying/digesting wood chips and feces produced by the beetles. I have never seen a passalid react to a mite on it (by scraping, rubbing, flinching, etc.).

"Some mites commonly found on passalids are merely phoretic (riding/hitchhiking) - immature, non-feeding forms that attach/glue themselves to various parts of the external structure, often at the ventral/lateral anterior corners of the elytra, or on the abdominal sternites. Some (e.g. uropodids) attach themselves by a stem as long as their body. Occasionally, one can find very lightly sclerotized, short-legged mites (different family) under the elytra, usually on the surface of the abdominal tergites. Again, I believe these are not known to damage the beetles.

"Another group of smaller mite species (often light-colored) are saprophagous, being attracted to the carcasses of dead passalids - but probably not being too particular about their food. These often swarm over the dead beetle, but I very much doubt that they are the cause of death. When I maintain passalids in the lab (or at home), I <always> have mites, and I don't worry about them - they don't bite humans and don't leave the passalid containers, unless stressed. If they really bothered one, they could be brushed off with a limp toothbrush or something similar - into a dish with soapy water, to keep them from scurrying away."

Q: When in SC, I see a fair number of these roaming across the roads at night. Are these males seeking females? Or vice versa? Or are they just trying to get to the other side?

"If this is in the spring and early summer, they are probably young adults of both sexes which have left their home logs and are seeking new ones in which to start galleries. An article a couple years ago reported pairs in flight at dusk (May, I think), with the males hanging in copulo beneath the females. I've only seen the U.S. species in flight a few times, and always singly."

Q: What is the gold-colored "fringe" on these beetles called? Does it serve any purpose?

"It's from long, orange setae on the prosternum, which extend laterally and are visible from above. I believe they <must> have a purpose, but it's not real obvious. Maybe it makes it easier to clean gunk off the body, or keep it from sticking in the first place. The amount of body hair varies a lot from species to species. Some are thickly setose along the sides of the elytra, as well. We don't use a specific term for it."


Oryctes' horn

Blister beetle

British stag beetles


Description of O. floridanus (PDF) from Florida Entomologist