As mentioned in an earlier post, the beetle ecology/physiology project has split into two separate sets of experiments. For the ecology project, I am hoping to get some good data regarding beetle abundance, seasonality and predation, but that will be the subject of other posts.
To get a more mechanistic understanding of heat stress in the beetles, I plan to do two sets of experiments once the beetles are available later in the summer. One will be a relatively straightforward measure of the range of temperature tolerance for the stink beetles (Amphidorini) and their non-stinky mimics (Asidini).
The other experiment will measure activity in the nervous systems of the beetles when they are under heat stress. There is considerable evidence that there is a blast of neural activity, sometimes referred to as a “spreading depolarization” when insects enter a state of paralysis known as heat coma. I would like the measure the temperature that is required for the spreading depolarization in the Amphidorini, which are relatively heat sensitive, and the Asidini, which are more resistant. The hypothesis is that it will take a higher temperature to induce spreading depolarization in the Asidini.
To get those data, I will need an amplifier to record neural activity in the beetles. Although I could spend a few thousand dollars on a new, ready made amplifier, there are some nice DIY designs in the literature. The circuit I chose (from Land et al., 2001, J. Neurosci Meth. 106:47) should do everything I need. It can amplify signals between 100X and 1000X, it has filters to stabilize the signal and reduce noise, and is relatively inexpensive to build.
The circuit diagram from the original paper is shown above. It uses two op-amps for amplification and filtering, and was designed to be powered by two 9V batteries. I will use the same circuit, but plan to use a 9V DC power supply for simplicity.
Most of the components arrived from Mouser Electronics today, and I can get started once a few more things (like the circuit boards) arrive. I plan to build one single channel amplifier to work out the process (little box on top), then assemble a four channel unit to record multiple beetles at once (bottom box).
The middle box will house the analog-to-digital converter (ADC), which will allow me to record the data on a computer.
I will post more details about the setup and procedures as things progress.
Special thanks to Dr. Hans Ruppel, whose support is making this project possible.
The western screech owls in Terry’s nest box are starting their spring activity. They seem to be slower getting started than in previous years. Nonetheless, there is nesting material in the box, and the male is hunting for food. Hoping for eggs soon!
If you want to see all the videos, including those from last year, go here.
After working very hard this winter to submit a manuscript describing the most recent results of the project, I realized that it has really become two non-overlapping lines of inquiry.
A few weeks ago, I submitted a manuscript titled “Batesian Mimicry and Thermal Resilience Among Tenebrionid Beetles from a New Mexican Piñon-Juniper Savanna” to the Journal of Experimental Biology. The editor said some kind words about it, but ultimately rejected it because it did not fit comfortably into the aims of the journal. The main complaint was that a significant portion of the paper focused on the ecology of the beetles, rather than their physiology.
It took a few days for me to realize that the paper had evolved into something different. Looking over the title, two things may stand out.
Batesian Mimicry
Thermal Resilience
Those are really two separate concepts and analyzing either one can be performed relatively independently of the other. In other words, this was two incomplete papers rather than one solid story.
Now begins the process of completing both of those stories.
Mimicry
Several lines of evidence address whether the Asidini Philolithus elatus and Stenomorpha rimata are Batesian mimics of the Amphidorine Eleodes obscura. For an organism to be a bona fide Batesian mimic it must
Resemble the model in the eyes (or ears or nose) of potential predators.
Be palatable
Be undefended (or at least to a potential predator)
Overlap the model in space and/or time so that predators can learn the association
Be relatively uncommon to prevent predators from discovering their mimicry
The Asidini fulfill these criteria to varying degrees
The major argument for mimicry is that the Asidini look a lot like E. obscura, and are about the same size and mass.
A close relative of S. rimata, S. marginata, has been shown to be palatable to mice and skunks. Palatability of P. elatus is unknown.
On the minus side:
P. elatus will regurgitate when handled, suggesting at least mild defense
Headstanding behavior, which contributes to the mimicry, is weak (P. elatus) or non-existent (S. rimata)
Both Asidini are at least as common as E. obscura during peak season, giving predators plenty of opportunity to learn that they are quite edible.
Stenomorpha rimata is present in late September and October, when Eleodes have disappeared from the surface, giving predators plenty of time to learn that they are tasty and undefended.
I really need to know who the local predators are, so that I can make sense of all this. I hope to use the upcoming field season to find out who is eating beetles around here. Based on scats and scattered body parts, someone is eating them, but who?
Thermal Resilience
Maintenance of scent glands is costly, so E. obscura should either use more metabolic energy than the undefended P. elatus and S. rimata, or devote less energy to other aspects of fitness. Based on respirometry across a range of temperatures it would appear that all three species use the same amount of energy per unit time, but the Asidini have much higher survival at elevated temperatures.
This is a nice partial story, but I need to know more about possible mechanisms. Two sets of experiments would be very helpful in completing this part of the story.
Testing survival across a full range of temperatures. I have only tested up to 40C, which is semi-lethal to Eleodes but does not strongly affect P. elatus or S. rimata. Although I am no fond of the idea, I need to test up to a temperature that is 100% lethal in order to have a complete picture of thermal resilience.
Because temperature induced lethality is associated with disrupted ionic regulation, it will be important to examine concentrations of ions in the hemolymph (blood) of E. obscura, P. elatus and S. rimata at high temperatures.
If all goes well, I should have two papers ready by the end of the season. Wish me luck.
Many of the darkling beetles here are members of model/mimic complexes. Specifically, some species of Eleodes, which can defend themselves chemically by using scent glands in their abdomens, serve as models for members of other genera, such as Philolithus and Stenomorpha, which do not have glands (Brown, 1971; Smith et al., 2015). In theory, the mimics are protected from predators by resembling the defended beetles, but save energy by not having to grow, maintain, and fill the glands. When a mimic resembles a defended species but does not have its own defense, it is referred to as Batesian mimicry.
As we look over the data from the past few seasons, it is worth considering some of the assumptions regarding models and mimics.
Advertising Bad Taste
Let’s start with the models, the chemically-defended Eleodes. If a species is noxious in some way, advertising this fact benefits both the prey and predator. If the predator knows that the prey is inedible, then the prey will avoid being eaten, and the predator avoids a mouthful of something nasty. Many noxious prey have bright, contrasting colors to make it easier to recognize them.
There are about six species of Eleodes commonly found here, and all have similar appearance and behavior. They are black, generally shiny, about 15 to 30 mm long (depending on the species), with variations in their body shapes and the patterning of the thorax and elytra (for an overview, see the local beetles page).
Eleodes obscura traveling across an open field. 7/9/25.
One could argue that uniformly black beetles are not very striking, and may therefore be doing a poor job of advertising their distastefulness. However, when walking about, they put little effort into concealing themselves, and a shiny black beetle is pretty easy to see on a background composed of shades of brown and drab green. Further, when approached the beetles stand on their heads to aim (and presumably show off) their scent glands.
Eleodes obscura reacting to an approaching threat by standing on its head. 8/17/24
These guys may not be as flamboyant as a coral snake or a lionfish, but they get the point across. After a few tries, a predator will probably get the idea that attacking one of these beetles will result in a face full of noxious chemicals.
The Mimics
From April to late July, the area is inhabited mostly by “honest” beetles, whose appearance and behavior truly reflect their ability to defend themselves. Starting in late summer/early fall, a group of “cheaters,” or mimics, starts to emerge. These are beetles that are about the same size and appearance as Eleodes, and in some cases act like them, but do not have defensive glands.
Eleodes obscura dispersa and Philolithus elatus infernus at the same scale. The elytra show similar patterns of ridges and punctures. Paint spots mark them for physiological studies.
One species, Philolithus elatus, is considered to be an accurate mimic of E. obscura. Both E. obscura and P. elatus have multiple geographic subspecies, and the patterning on the elytra of each P. elatus subspecies resembles that of the E. obscura subspecies that shares its range (Brown, 1971). In the example above, the elytra of P. elatus infernus found in Santa Fe have weakly defined ridges, similar to those of the local E. obscura dispersa.
Philolithus emerges in late July and is abundant through August and early September. This means that predators have had since the beginning of April to sample Eleodes and learn that shiny black beetles taste bad. Another supposed mimic of E. obscura, Stenomorpha marginata, emerges even later, in late August and is present in September and October.
Stenomorpha marginata. 9/3/25.
At first glance, the mimics could easily be mistaken for E. obscura, and a predator might pass them by. At other loacations, it is reported that both species even mimic the headstanding behavior of Eleodes (Brown, 1971; Smith et al, 2015). Here in Santa Fe, it takes physical contact (rather than a close approach) to get P. elatus to respond, and even that is half-hearted.
Philolithus elatus giving its best effort at a headstand.
Stenomorpha marginata bracing for whatever comes next. 10/1/25.
Stenomorpha does not even bother with a lame attempt, and just extends its legs outward to brace itself when touched.
Another mimic produces more convincing headstands. Moneilema appressum, the cactus longhorn beetle, is a member of a completely separate family of beetles (Cerambycidae). Nonetheless, its smooth, shiny appearance and willingness to stand on its head when approached make it a convincing mimic of Eleodes longicollis.
Eleodes longicollis raising its abdomen in response to an approaching experimenter.
Moneilema appressum performing a convincing headstand. 8/20/25.
All of this leaves a few open questions.
First, how good does mimicry really have to be? From April to August, just about every shiny black beetle that a predator encounters is chemically defended. Do Philolithus and Stenomorpha need to imitate the appearance and behavior of Eleodes all that precisely, or is it enough to be a shiny black beetle of about the right size and shape? Based on scat found around here, someone is definitely eating Eleodes, so it’s likely that some mimics will get eaten anyway.
The fact that Moneilema seems to do a better job of looking and acting like an Eleodes species is intriguing, although I am not sure what to conclude at the moment.
Philolithus elatus regurgitating in response to handling. 8/11/25.
Second, are the mimics truly undefended? Philolithus will regurgitate when handled roughly, which, at least for grasshoppers, qualifies as chemical defense. Further, they feed, oviposit, and their larvae probably live among harvester ants (Pogonomyrmex sp.) during their development (McIntyre, 1999; Slobodkovich, 1979). It seems plausible that the beetles acquire some sort of chemical signature from the ants that deters attacks by the ants and other predators.
Stenomorpha, on the other hand, appears completely undefended. I have not observed them to regurgitate, they do not appear to associate with ants, and they do not have scent glands. They may be less vulnerable because they emerge so late in the season, but we will need to know more about their predators to have any insight into this.
References
Brown, K. W. (1971). A population approach to computer taxonomy with applications in the genus Gonasida.
McIntyre, N. E. (1999). Use of Pogonomyrmex nest-sites by Tenebrionid beetles (Coleoptera: Tenebrionidae) for oviposition and thermoregulation in a temperate grassland. The Southwestern Naturalist44, 379–382.
Slobodchikoff, C. N. (1979). Utilization of Harvester Ant Debris by Tenebrionid Beetles. Environmental Entomology8, 770–772.
Smith, A. D., Wilson, J. S. and Cognato, A. I. (2015). The evolution of Batesian mimicry within the North American Asidini (Coleoptera: Tenebrionidae). Cladistics31, 441–454.
Because it took so long to load when they were all on the same page, I have moved the owlet videos to new a series of pages. It’s slightly more hassle if you want to see all of them at one sitting, but it beats waiting what seems like forever for the pages to load. If you love it or hate it, use the contact link to send feedback.
More owl feedings. We are in the waiting period before the eggs hatch. The female sits on the eggs continuously except for short breaks. The male brings her mice and occasionally insects. Here are a couple clips of food deliveries.
In the first one, you can get an idea of how long their legs are as she stands up to peer out the hole before he arrives with a kangaroo mouse
In another clip, she is away when he pops in with a Jerusalem cricket (“potato bug”).
And a clip where she swallows most of a mouse that was leftovers.
4/22/25: We Must Be Getting Close!
No owlet hatching yet, hopefully tonight to still meet my prediction.
In the meantime, here are two clips of mice deliveries: a kangaroo mouse and a field mouse from a few days earlier.
Field mouse delivery. 4/19/25.Kangaroo mouse. 4/21/25.
The female has been spending all her time on the eggs and the last morning she has been fussing with them almost continuously and skipped her usual pre-dawn break. Maybe sensing the movement of the chicks inside?
Last fall, we gathered data on the physiology, temperature sensitivity and lifespans of Eleodes obscura and its presumed mimic Philolithus elatus. The data were interesting and I have drafted a paper, but it seemed worth trying to replicate the results to be sure the data were solid.
One of the limitations of working with a seasonal organism, like P. elatus, is that one can only work during a narrow window, when the animals are available and alive. True stink beetles, like E. obscura, survive for years, so one can simply collect a bunch and then do experiments almost indefinitely. Philolithus die less than two months after emerging, then are completely gone until late the next summer.
Hence my excitement at finding the first P. elatus of the season.
The first Philolithus elatus collected in 2025. 7/27/25.
More are emerging every day. We now have seven P. elatus available for experiments, and are hoping to bring the total to twenty within the next week. There are plenty of E. obscura available as well. We should soon have a big pile of data to add to the manuscript.
For a little more info on P. elatus, check out the new Wikipedia page that I started.
The islands in the Gulf of California provide a natural laboratory for the effects of “spatial subsidy,” the movement of resources from a rich environment (the sea) to a more impoverished habitat (the desert islands). In this context, scientists have studied many species on the islands, including Tenebrionid beetles. The abundance and diversity of beetles on the islands of Bahia de los Angeles have been surveyed for at least 30 years, and my good friend and colleague Dr Drew Talley has been leading the studies for most of that time. In recent years, Dr Natalia Rodriguez Revelo, an expert in beetles and dune ecology, has participated in the work with Drew. I have participated in various roles for several of the past 20 field seasons, and was once again privileged to spend time with them and help out on the islands this year.
Drew and Natalia counting beetles on La Ventana. 6/28/25.
The procedure is straightforward in principle: on each island, set multiple pitfall traps (plastic party cups) baited with lean pieces of fish. The beetles (and, occasionally, other creatures) fall into the traps. Six days later, the traps are checked and the number and species of beetles are scored. In practice, mice or gulls can steal bait if it is not adequately secured, or fat from fish guts can turn the contents of the cup to smelly soup.
In a perfect world, traps would be set on all of the accessible islands in the bay. In practice, time constraints forced us to prioritize. This year, we sampled Coronadito, Coronado (also known as Isla Smith), Flecha, Pata, Llave, Cerraja, La Ventana, Cabeza de Caballo, and Gemelos West.
I made an effort this year to photograph each species using a platform with tacky wax to secure the beetle, and a scale to document its size.
Map of the bay at Bahia de los Angeles. Most islands, including all islands sampled this year, are labeled. The town of Bahia de los Angeles is labeled at lower left.
It was marginally successful, and provided insight about how to improve future versions.
Below is a draft guide to the beetles found on the islands, When possible, photos are provided of beetles held in fingers and mounted on the photography platform. Cartoons provide graphic representation of the relative sizes of the beetles, ranging from tiny (Batuliodes) to hefty (Cryptoglossa), keeping in mind that the sizes of all species can vary significantly.
Distribution of each species are based on data from Sanchez Piñero and Aalbu (2002). A table extracted from their observations can be found here.
Click the photographs if you want to see larger versions.
Argoporis apicalis
Medium sized, with ridged elytra and reddish legs. Argoporis is one of the few Tenebrionids on the islands which possess defensive glands in their abdomens.
Found on all islands except Mitlan (tiny island next to Coronado).
12 mm
Argoporis apicalis trapped on Coronadito island. 6/26/25.
Argoporis apicalis trapped on Cerraja island. The blurred image of an extra antenna was caused by using focus stacking to improve depth of field. 6/27/25.
Batuliodes confluens
This tiny brown beetle with roughened pronotum and elytra.
Found on the majority of islands, and may be undercounted due to its small size.
~3 mm
Batuliodes confluens trapped on Flecha island. 6/23/14
Batuliodes confluens trapped on Cerraja island. 6/27/25.
Cryptadius tarsalis
Small, oval, and deep-bodied, with dense rows of small punctures on the elytra.
Cryptadius is found on Bota, Cerraja, Coronado, Jorobado, Mitlan and Pata.
8 mm
Cryptadius tarsalis.trapped on Llave island. Scale bar, 2 mm. 6/27/25
Cryptoglossa spiculifera
One of the largest beetles on the islands, with elytra decorated with rows of raised, spiny bumps.
Found on the largest islands (Coronado, Cabeza de Caballo, but not La Ventana) as well as the rookery island, Gemelos West.
28 mm
Cryptoglossa spiculifera trapped on Gemelos West island, 6/28/25.
Cryptoglossa spiculifera trapped on Gemelos West island. Scale bar, 10 mm. 6/28/25.
Microschatia championi
Slightly smaller than Cryptoglossa, the elytra of Micoschatia are decorated with dimples rather than sharp bumps and there are punctures on the lateral pronotum of M. championi.
Present on all but the smallest islands.
20 mm
Microschatia championi trapped on Cerraja island. 6/27/25.
Microschatia championi trapped on Cerraja island. Scale bar, 5 mm. 6/27/25.
Stibia sparsa
Shaped like a typical Tenebrionid, with dense punctures on the pronotum and rows of punctures on the elytra.
Stibia can be found on the largest islands (Cabeza de Caballo, Coronado, La Ventana) plus Gemelos West.
11 mm
Stibia sparsa trapped on Gemelos West island. 6/28/25
Stibia sparsa trapped on Gemelos West island. Scale bar, 2 mm. 6/28/25.
Tonibius sulcatus
Very small and reddish, with relatively smooth pronotum and strongly ridged elytra.
Described from most islands, except Coronaditio, Gemelos West, Jorobado and Llave.
6 mm
Tonibius sulcatus found at Las Hamacas hotel. 7/10/24.
Triphalopsis californicus
Small, black, oval, and deep-bodied. Covered with fine hairs that are often coated in dust.
Triphalopsis has been described from all islands except Gemelo West.
8 mm
Triphalopsis californicus trapped on Flecha island. 6/27/25.
Triphalopsis californicus trapped on Cerraja island. Scale bar, 2 mm. 6/27/25.
There are many other beetles, including various species of Histeridae and Dermestidae (not shown).
Hister Beetle on Coronadito Island. Scale 2 mm. 6/26/25.
Centipedes, spiders, and scorpions are often found in the traps in the larger islands.
Scorpion trapped on La Ventana. 6/28/25
References
Sanchez Piñero, F. and Aalbu, R. L. (2002). Tenebrionid Beetles (Appendix 6.1). In A New Island Biogeography of the Sea of Cortés, pp. 129–153. New York: Oxford University Press.
A little bit of physiology to start off the summer.
We are gearing up to complete the data sets for local beetles this fall. Ultimately, we’ll be comparing metabolism of two Eleodes species, E. obscura and E. longicollis, with those of a few mimics, Philolithus elatusand Stenomorpha marginata. The data from last fall were very interesting, but after drafting the manuscript it was clear that another season of data would help to clarify the results.
Because of seasonal availability, comparing Eleodes with their mimics will have to wait until late summer and early fall. Eleodes longicollis is common all summer, but E. obscura becomes much more common in July. Philolithus elatus and S. marginatus will not appear until the end of July at the earliest.
In the meantime, there were a couple of other species available in the lab that will help in understanding the data from Eleodes, Philolithus, and Stenomorpha.
Zophobas morio. Yellow paint on right elytra is for individual identification.
Zophobas morio, also known as the “superworm,” is originally from the American tropics. It is widely cultured as a food for pets and is being considered as a source of protein for humans. A colony was established in the lab in early 2024, so they are available for experiments any time. Being from the neotropics, with consistently warm and relatively wet conditions, they are expected to respond more strongly to temperature changes.
Asbolus verrucosus, the blue death-feigning beetle.
Asbolus verrucosus, called the blue death-feigning beetle because of its tendency to play dead when handled, is a long-lived species from the hot, dry deserts of southwestern North America. We received a cohort from Bugs in Cyberspace in January, and they have spent the past few months adjusting to handling and conditions in the lab. Their adaptations to extreme conditions suggest that they will be tolerant of high temperatures.
Oxygen consumption was measured for the two species from 15°C, at which beetles should be slow and sluggish, to 40°C, just below the lethal temperature for a close relative of A. verrucosus (Cryptoglossa muricata; Ahearn, 1970). Therefore the temperature range may cause cold stress at at the low end and heat stress on the high end, but was not expected to be lethal.
The two species are just about the same size and mass, with each being somewhat over half a gram. Twelve beetles of each species were tested at each temperature, although technical issues reduced this to eleven in a few cases. The respirometer could handle eight beetles at a time, so four of each species were tested together each day, and each temperature required three days of experiments.
Oxygen consumption of Z. morio and A. verrucosus between 15°C and 40°C. Each point shows the mean and standard error of 11-12 beetles, with most error bars smaller than the symbols. At each temperature above 15°C, Z. morio consumed more O2 than A. verrucosus. At 40°C, all Z. morio were visibly impaired immediately after experiments, and 8/12 were dead within two days. None of the 12 A. verrucosus showed any signs of stress after 40C experiments, and all survived indefinitely (one week so far) after being returned to their enclosure.
At 15°C, O2 consumption was identical for the two species. At every other temperature, Z. morio consumed significantly more O2 than A verrucosus. This may reflect a lower standard metabolic rate for the desert species, which is adapted to an environment with limited resources. Neither species showed any sign of stress at either 25°C or 35°C, in that both emerged from experiments active and coordinated, and none died in the three days between experiments.
The two species diverged further at 40°C, with Z. morio dramatically increasing their O2 consumption (note the log10 scale), while O2 consumption in A. verrucosus increased only slightly. Importantly, all Z. morio were visibly impaired at the end of 40°C experiments, showing slow, uncoordinated movement or no movement at all. Eight of twelve Z. morio were dead within two days. In contrast, none of the A. verrucosus tested at 40°C appeared to be stressed, and all survived indefinitely.
It is perhaps not surprising that Z. morio, a species originating from a relatively constant, resource rich environment, has a higher metabolic rate and is more sensitive to environmental temperature than the desert beetle, A. verrucosus. The dramatic increase in O2 consumption and lethality between 35°C and 40°C for Z. morio was quite striking, however. The lethality-associated increase in metabolic rate resembles that in the fruit fly, Drosphila melanogaster at 35°C (Sandstrom et al., unpublished), and indicates that a dramatic increase in O2 consumption may be a common indicator of severe heat stress in insects.
There are a few possible caveats. For example, although the two species have been kept under the same conditions for at least four months, which should be enough to reduce the effects of previous physiological adaptations, their life histories as larvae and pupae were different. Z. morio have been reared for multiple generations at the lab, while A. verrucosus were collected from the wild, which may somehow influence their responses to temperature. Asbolus and their relatives can be reared in captivity (Rider, 2024), so it may be worth repeating the experiment with lab-reared beetles.
References
Ahearn, G. A. (1970a). Changes in hemolymph properties accompanying heat death in the desert tenebrionid beetle Centrioptera muricata. Comparative Biochemistry and Physiology33, 845–857.
Rider, S (2024) Death Feigning Beetles of the United States and Mexico. Publisher S. Rider Jr. 182 pp.
Although the screech owls have been hogging all the attention this spring, many more birds are raising families in the area. Spotted towhees, Bewick’s wrens, lesser goldfinches, and chipping sparrows can be observed singing their songs and collecting food for their offspring.
We have been very lucky to have a clear view of a pair of western bluebirds. There has been a nest box on the back lot for many years. Last fall, it was time to replace the old, battered box with a new one, and the birds settled in early this spring.
Female western bluebird on nest box. 3/11/25.
They were getting things ready by the beginning of March.
Bluebirds staking out their nest on a cold spring morning. 3/15/25.
Despite the cold, they were ready to get started. Note the fluffed feathers in the photo above.
Mom peeking out of the box. 4/25/25.
The process was largely mysterious, with the parents coming and going during April and May, but no sightings of the nestlings.
The babies finally started sticking their heads out in May. Mom and dad brought food on a regular basis/
Nestling ready to test its wings and become independent. 5/23/25.
By the last part of may, the kids were ready to see the world. Within a day of showing their heads, everyone was gone.
Female starting the next nest. 5/29/25.
I cleaned out the old nest a few days after the fledglings left, and was surprised to see a pair of bluebirds bringing new materials less than a week later. It is impossible to say whether these are the same parents, but it seems likely. They can often raise more than one clutch per year, so maybe we’ll see more fledglings in a few months.
