Caring For and Rearing Moneilema armatum (Coleoptera: Cerambycidae) (original) (raw)

Caring For and Rearing Moneilema armatum (Coleoptera: Cerambycidae)

Dedicated to Heather Doyle, who spotted my very first Moneilema armatum while we were in the field searching for groovy spiders.

Moneilema armatum (LeConte 1853) classification:
Coleoptera order » Polyphaga » Chrysomeloidea » Cerambycidae » Lamiinae » Moneilemini tribe

Moneilema armatum on Opuntia:

Moneilema armatum name:
The generic name Moneilema (Say 1824) was published by American entomologist Thomas Say in 1824 in the Journal of the Academy of Natural Sciences of Philadelphia, Volume 3, pp 403-462, in his Descriptions of coleopterous insects collected in the late expedition to the Rocky Mountains. In this publication, Say includes the species Moneilema annulata (Moneilema annulatum), found in the Missouri territory. This species is currently designated as the type species (Whittaker, 2022). What does the generic name mean? Named for a person? A location? I have no clue – please inform me.

Mawdsley (1993) notes that the Neotropical Mexico species Moneilema inaequalis (Say 1835) is one of the surviving 770 specimens in the collection of Thomas Say housed in the Museum of Comparative Zoology at Harvard University, Cambridge, Massachusetts. M. inaequalis was initially listed as the type species by Lacordaire, published in 1869 (Gutiérrez, 2020).

Naturalist Thomas Say (1787-1834) is renowned worldwide for his work in entomology, herpetology, conchology, paleontology, and more. He was assisted in large part by his wife, scientist and artist Lucy Say (circa 1800-1886), whose stunning illustrations can be found online and in collections. Other than a few short online articles, I do not find much written about Thomas Say's remarkable life and work apart from a 1992 biography by Patricia Tyson Stroud and a 1931 biography by Harry B. Weiss and Grace M. Ziebler. If I do find Mr. Say hard at work in the Library of Heaven, I will ask him about the generic name of Moneilema.

The specific epithet, by contrast, is refreshingly simple: armatum (Latin: armatus, armata = armed, equipped), a nod to the beetle's pronotal spines.

Moneilema armatum: female and male (with water droplets around pronotum)

I have not reared Moneilema armatum from egg to adult. At the time of this writing in mid-winter 2025, I am maintaining an overwintering cage, but it is unlikely that I still have living larvae or pupae. I have chosen not to disturb the cage just in case someone is alive in there. So I have only collected adults and gotten a few eggs who hatched into larvae.

In the discussion below, I describe my experience in Finding, Housing and Care, Life Cycle, and Observations.

Moneilema armatum in the field:

FINDING Moneilema armatum

I collected around a dozen adult Moneilema armatum on and near Opuntia. The first one I collected was on 04.29.2024:

Moneilema species are found in arid and semi-arid environments on and around cactus plants, especially Opuntia and Cylindropuntia species. These beetles are largely crepuscular and I found most of mine early in the morning where they had overnighted on cacti or were just beginning to move to hiding places for the daylight hours.

Moneilema in natural habitat:

Here you can see munchie marks on Opuntia that might be a sign of nearby Moneilema within their habitat:

Side Note: I noticed that several individual cactus pads in the area where I spotted the adults displayed a bit of mysterious hardened black muck, usually at the top of the pad. An amateur website that I had read (but with only a single notation and lacking references) associated the black muck with the presence of Moneilema larvae. Is that possible? Perhaps a reader of these forums can enlighten me.

Mystery muck on Opuntia:

HOUSING and CARE

The initial enclosure for my adult Moneilema armatum beetles was a glass ten-gallon terrarium with a steel mesh top. I added a thick substrate of a coconut fibre / sand / soil mixture. I kept the beetles fed with fresh Opuntia pads.

Initial enclosures for adult beetles:

For moisture, I very lightly misted the enclosure with a fine-mist spray bottle and I provided water sponges for drinking. However, I believe that the beetles get the moisture they need directly from the succulents.

I added fresh apple slices each morning and also brought home cactus roots, flowers, and stems to add to the enclosure.

This newly-adopted fellow (I believe) is happily munching on cactus:

LIFE CYCLE

Note: I did not get pupae: only adults, eggs, and larvae.

Egg

Moneilema armatum eggs are beige to light tan, slightly oblong (somewhat similar in shape to a chicken egg), and measure around 5 mm. Females lay eggs individually in or near the base of the cactus. In captivity, my beetles laid eggs directly atop the cactus root inside the enclosure.

Moneilema armatum egg freshly laid:

These two eggs were laid near each other on cactus root:

This egg is in dirt beside the cactus root:

Larva

I got very few larvae from my very few eggs. After hatching, the larvae would eat their way into cactus pads and work on hollowing them out.

Larval entrance on an older (softer) Opuntia pad:

Moneilema armatum larva:

slightly older larva:

and slightly older larva:

and then even older larvae:

Adult

From what I could see, the season for these beetles is early and adults are relatively short-lived compared to many of the beetles I have raised. I began collecting adults in April and most had died off by the end of summer.

Mating:

It was common to see my Moneilema beetles mating. Because these guys are such agile climbers on smooth glass, they often went to the top of the cage to crawl upside down on the steel mesh top and mated in that position. I observed that these beetles remain in copula for several hours. For example, I watched the pair in the images below first engage at 9:18am and not separate until just after 4:00pm.

Moneilema armatum mating:

Here the male climbs atop the female followed by copulation:

Not all mating attempts are successful for various reasons. In this case, the gentleman simply hasn't read the manual:
VIDEO of Moneilema armatum mating attempt

The gentleman below, however, is having success. There's not much movement here, but the couple will remain in copula for hours:
VIDEO of Moneilema armatum mating pair

This female is clinging to the top of the cage immediately after mating. It appears to me that a spermatophore is attached:

Laying Eggs:

Females lay individual eggs in or on the cactus plant.

Moneilema armatum laying egg:

VIDEO of Moneilema armatum laying egg in cactus root

At the time of this writing, I am maintaining the enclosure just in case any pupae were able to form.
My current overwintering cage for Moneilema armatum:

OBSERVATIONS

Climbing

One thing that I found fascinating is the remarkable ease with which these guys can walk up smooth glass. I have housed a number of insects in glass terraria and I rarely have someone (other than snails, who are honorary insects) climb up the glass. These beetles are perfectly comfortable climbing the glass and hanging upside down at the top of the enclosure. Of course, for rearing purposes, you will want to exercise caution when opening the enclosure, as the beetles are more than happy to escape from the top.

Sound

For me, the most intriguing characteristic of these insects is their use of sound. Most Cerambycidae have stridulatory devices that allow them to produce sounds. As one might expect, the frequency, pulse length, and intensity each vary by species (Finn et al., 1972). Some Cerambycidae create sound by rubbing the ridged hind femora against the elytral margins while others produce sound using the pronotum. Lamiinae subfamily beetles, to which the Moneilema species belong, produce sound by creating friction between the plectrum, the "scraper", inner side of the posterior pronotal margin, and the pars stridens, the "file", a striated plate on the mesoscutum (Hepp at al., 2019).

Wei et al. (2024) seek to use sound recognition with the corresponding variations in stridulatory organ morphology in order to better identify and classify Cerambycidae. Their detailed study on three different Lamiinae species demonstrate both interspecies and intraspecies variation in the morphology of stridulatory organs.

Hepp at al. (2019) note that sound in Cerambycidae is mainly produced as a startle response to predators, but that sounds may also be produced during courtship and copulation. I observed both occurrences in the Moneilema armatum that I cared for.

I do not have proper recording equipment to capture the beetles' sound production, but I captured this, just a few seconds of sound only, no video:
Moneilema armatum SOUND ONLY, no video

Here, you can see just a bit of the sound production of a copulating male (caution: there are other louder animals also talking here):
VIDEO of Moneimela armatum producing sound.

And just one tiny sound here:
VIDEO: Tiny Sound.

And nothing but a blur here:
VIDEO: Useless Blur with Sound

Most often, these guys produced sound if I had to handle the beetles, generally to return them to a safe location if they were being extra feisty. Additionally, but to a lesser extent, the Moneilema produced sound in their interactions with each other, including in courtship and mating.

Roommates

In my experience with Moneilema armatum, I found that they get along quite well with each other, without bickering or disputes. Even though the enclosure was sufficiently large for the small number of beetles I collected, the beetles often chose to congregate in close proximity to one another.

Moneilema armatum inside enclosure:

I collected this fellow with a bum leg. He is still able to walk around the cactus plant and to eat, and he lived a good Moneilema life. He makes a tiny sound in this video:
VIDEO of Moneilema armatum

Overall, these beetles are easy to care for and are strikingly beautiful and interesting animals. They would be good "pet" beetles for anyone looking to adopt an especially sweet insect, as long as you have good access to their host plants.

Side note: Propagating Opuntia from Cuttings

I made several cactus starts from individual Opuntia pads. You can gently twist off healthy Opuntia pads from cacti in natural areas (at safe locations without pesticides, of course). An easy way to handle Opuntia pads while in the field is with tongs. Let the pads dry for a few days so that the wound calluses over in order to prevent rot from too much moisture. Place the callused end in a good, well-drained cactus mix (soil + sand + perlite). Water lightly and place in a windowsill or similar spot where the plant can get gentle sunlight.

These plants are quite useful to a variety of insects that you might wish to rear.

Moneilema armatum happily munching on Opuntia:

References

Finn, Warren E., Mastro, Victor C., & Payne, Thomas L. (1972). Stridulatory Apparatus and Analysis of the Acoustics of Four Species of the Subfamily Lamiinae (Coleoptera: Cerambycidae), Annals of the Entomological Society of America, Volume 65, Issue 3, Pages 644–647. https://doi.org/10.1093/aesa/65.3.644

Gutiérrez N, Toledo-Hernández VH, Noguera FA. 2020. Four new species of Phrynidius Lacordaire (Coleoptera, Cerambycidae, Lamiinae) from Mexico with an identification key for the genus. Zookeys. 1000:45-57. doi: 10.3897/zookeys.1000.56757. Erratum in: Zookeys. 2022 Mar 18;1089:181-186. doi: 10.3897/zookeys.1089.80564. PMID: 33354134; PMCID: PMC7728726.

Hepp F, Bezerra AM, Botero JP. First description of sound emission of Rhaphiptera affinis Thomson, 1868 (Cerambycidae: Lamiinae: Pteropliini). Zootaxa. 2019 Mar 18;4567(3):zootaxa.4567.3.9. doi: 10.11646/zootaxa.4567.3.9. PMID: 31715889.

Mawdsley, Jonathan. 1993. The Entomological Collection of Thomas Say. Psyche: A Journal of Entomology 100, 10.1155/1993/59616. https://onlinelibrary.wiley.com/doi/10.1155/1993/59616

Say, Thomas. (1824). Descriptions of coleopterous insects collected in the late expedition to the Rocky Mountains. Journal of the Academy of Natural Sciences of Philadelphia, 3, 403--462. https://www.biodiversitylibrary.org/part/245011

Wei, J.-Q., Wang, X.-Y., Zheng, X.-L., & Tong, X. (2024). Stridulatory Organs and Sound Recognition of Three Species of Longhorn Beetles (Coleoptera: Cerambycidae). Insects, 15(11), 849.

Whittaker, A. (2022). Moneilema semipunctatum (cactus borer beetle). CABI Compendium. https://doi.org/10.1079/cabicompendium.120558

For Further Reading

Davranoglou, Leonidas-Romanos, Taylor, Graham, & Mortimer, Beth. (2023). Sexual selection and predation drive the repeated evolution of stridulation in Heteroptera and other arthropods. Biological Reviews, 98, 10.1111/brv.12938.
https://www.researchgate.net/publication/368511026\_Sexual\_selection\_and\_predation\_drive\_the\_repeated\_evolution\_of\_stridulation\_in\_Heteroptera\_and\_other\_arthropods

Luo, C., & Huang, S. (2021). Stridulatory sound production and acoustic signals of the longhorn beetle Batocera lineolata (Coleoptera: Cerambycidae). Bioacoustics, 31(2), 148–159. https://doi.org/10.1080/09524622.2021.1890640

Smith, C. I., & Farrell, B. D. (2005). Range expansions in the flightless longhorn cactus beetles, Moneilema gigas and Moneilema armatum, in response to Pleistocene climate changes. Molecular Ecology, 14(4), 1025–1044. https://doi.org/10.1111/j.1365-294x.2005.02472.x

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