Beetle Collecting 101: Fermenting bait traps for collecting longhorned beetles

One of the most useful collecting techniques for those interested in longhorned beetles (families Cerambycidae and Disteniidae) is fermenting bait traps. I was first clued into the use of such traps soon after I began collecting these beetles in the early 1980s and encountered a series of rather old publications by A. B. Champlain and S. W. Frost detailing their usefulness and the diversity of species found to be attracted to them. Champlain & Kirk (1926) listed 15 species of Cerambycidae attracted to bait pans containing a mixture of molasses and water. This list was expanded to 37 species by Champlain & Knull (1932), who noted that a mixture of one part molasses to ten parts water in a gallon-pail seemed to give the best results. Frost & Dietrich (1929) listed 20 species captured with a mixture of one part molasses to 20 parts water. Twelve of the species they mentioned were not listed by Champlain & Knull (1932), and the list of Frost (1937) included two additional previously unrecorded species.

I made extensive use of fermenting bait traps during my 1980s survey of longhorned beetles in Missouri (MacRae 1994) using a mixture of one part molasses, one part beer, nine parts tap water, and a sprinkling of dry active yeast to start fermentation. This recipe was based on that of Champlain & Knull (1932) (although I must confess that I do not remember where I got the idea to add beer and yeast). During that study, I collected 13 species of longhorned beetles using this method and found in other collections specimens of three additional species also collected with fermenting baits. Of the species I collected, the most significant was a large, attractive Purpuricenus that closely resembled P. axillaris (which was also collected in the traps) but clearly was not that species. These eventually proved to be undescribed after I was able to examine type material in the Museum of Comparative Zoology at Harvard University, leading to a review of the genus in North America and the description of the new species as P. paraxillaris (MacRae 2000). Since then I’ve employed fermenting bait traps to collect Cerambycidae in other parts of the country (MacRae & Rice 2007), and I now have records of 72 species of U.S. Cerambycidae documented as being attracted  to fermenting baits.

Molasses-beer fermenting bait trap

Molasses-beer fermenting bait trap.

My interest in this technique was renewed some years ago when I finally succeeded in collecting the spectacular Plinthocoelium suaveolens in fermenting bait traps placed on glades in extreme southwestern Missouri. During my Missouri survey, I had done the bulk of my bait trapping along the edges of glades just south of St. Louis in Jefferson County, and while I had a record of this species in those glades I had never collected it there myself. Finally, last year I observed one of the host trees (gum bumelia, Sideroxylon lanuginosum) on these glades with the characteristic P. suaveolens larval frass pile at the base of the trunk, prompting a renewed effort this past season to collect the species there using fermenting bait traps. In early June I placed a series of traps at Valley View Glades Natural Area (~4 miles NW of Hillsboro) and Victoria Glades Natural Area (~2.5 miles S of Hillsboro). At both locations four traps were placed along the upwind interface between dry, post oak woodland and dolomite glades. Traps were spaced about 50–100 yards apart and hung to ensure exposure to sunlight but minimize the chance they would be discovered by vandals. Each trap consisted of a 2-L plastic bucket with a small hole drilled near the rim on each side and a length of wire attached to allow hanging from a nail in the side of a tree. Two baits were used: 1) molasses/beer, and 2) red wine. The molasses/beer recipe was based on Guarnieri (2009)—more concentrated that what I have used previously, and was prepared by combining a 12-oz (355 mL) jar of dark molasses with an approximately equal volume of tap water in a 1-L plastic bottle, agitating thoroughly, and bringing to one liter volume with tap water. At the trap site, about 500 mL of diluted molasses was added to the trap, followed by a 12-oz can/bottle of beer and one-half of a 7-g packet of dry, active yeast. Red wine bait was a cheap jug variety, undiluted, with about 500 mL added to the trap. Molasses/beer and red wine were alternated in the traps at each location and replaced every two weeks or if excessively diluted by rain or evaporated during hot, dry conditions. Traps were checked weekly from early June to mid-September by pouring the trap contents through a kitchen strainer over an empty bucket and transferring beetles with forceps to empty vials. Once back at the vehicle, tap water was added to each vial and the vial agitated to rinse the specimens and remove bait residue. The water was decanted and the beetles blot-dried with paper towels before transfer to clean vials containing tissue and ethyl acetate to halt decay and maintain the beetles in a relaxed state for pinning.

Cerambycidae from fermenting bait trap

A charismatic trio of Cerambycidae from fermenting bait traps at Victoria Glades: Purpuricenus paraxillaris (left), Plinthocoelium suaveolens (center), and Stenelytrana emarginata (right).

A note about my preferred trap design. I have always used open-top buckets (previously 1-G metal, now 2-L plastic), but “window jugs” (i.e., ½-G milk or juice jugs with holes, or “windows”, cut in the sides) are also commonly used. I have not directly compared buckets with window jugs; however, I favor buckets because I believe beetles attracted to window jugs are more likely to “perch” on the trap itself rather than fall directly into the bait. I also believe that beetles, once trapped, are more likely to escape from window jugs because the window edges provide “grab” sites for beetles before they succumb. The risk of escape can be reduced if the bait surface lies well below the bottom edge of the windows, but this then limits the quantity of bait that can be used. In my experience, 500–750 mL is the minimum volume of bait that is needed to last the duration of the two-week fermentation cycle without evaporating to the point that it is not deep enough to quickly submerge beetles falling into it. Some may be concerned that open-top buckets are prone to dilution by rain, but in my experience this happens infrequently and I have not noticed diluted bait to be any less effective at attracting beetles. Rain shields, on the other hand, only serve to provide a potential perch for beetles attracted to the trap.

Plinthocoelium suaveolens

Plinthocoelium suaveolens captured in flight near its host tree, gum bumelia (Sideroxylon lanuginosum), at Victoria Glades.

A total of 558 longhorned beetles representing 16 species were collected from the traps over the course of the season (see list below). Of these, 339 specimens representing 14 species were attracted to molasses/beer, while 219 specimens representing 14 species were attracted to red wine. Ten species were represented by more than two specimens and were attracted to both bait types, the most desirable being Plinthocoelium suaveolens (41 specimens), Purpuricenus axillaris (20 specimens), P. paraxillaris (3 specimens), and Stenelytrana emarginata (6 specimens). The number of P. suaveolens collected is remarkable, considering that it was not collected during my previous trapping effort spanning several years in the 1980s. It may be significant that 1) the molasses/beer recipe used in this study was considerably more concentrated than that used in the 1980s, and 2) nearly twice as many specimens were collected in red wine (not used in the 1980s) compared to molasses/beer. I routinely examined the gum bumelia trees during my weekly visits in an attempt to find adults on their host, especially during flowering, but encountered only a single adult in flight near one of the trees—a curious result given the diurnal habits and large, conspicuous appearance of the adults. All other species collected in numbers were more attracted to molasses/beer, with the significant exception of Purpuricenus paraxillaris. Seven species taken this season were not detected with fermenting bait traps in the 1980s, bringing to 23 the number of species collected by this method in Missouri. One species, Strangalia sexnotata, is documented from fermenting bait for the first time in this study.

2015 fermenting bait trap catch

2015 fermenting bait trap catch, box 1 of 3 (click to enlarge).

2015 fermenting bait trap catch, box 2 of 3 (click to enlarge).

2015 fermenting bait trap catch, box 2 of 3 (click to enlarge).

2015 fermenting bait trap catch

2015 fermenting bait trap catch, box 3 of 3 (click to enlarge).

Longhorned beetle species and numbers taken in fermenting bait traps in 2015—most to least abundant (MB = molasses/beer, RW = red wine):

  1. Elaphidion mucronatum – 254 (MB = 176, RW = 78)
  2. Eburia quadrigeminata – 145 (MB = 73, RW = 54)
  3. Plinthocoelium suaveolens – 41 (MB = 14, RW = 27)
  4. Neoclytus scutellaris* – 32 (MB = 26, RW = 6)
  5. Parelaphidion aspersum – 26 (MB = 18, RW = 8)
  6. Purpuricenus paraxillaris – 20 (MB = 6, RW = 14)
  7. Orthosoma brunneum – 13 (MB = 8, RW = 5)
  8. Neoclytus mucronatus* – 8 (MB = 6, RW = 2)
  9. Stenelytrana emarginata* – 6 (MB = 5, RW = 1)
  10. Purpuricenus axillaris – 3 (MB = 2, RW = 1)
  11. Enaphalodes atomarius – 2 (MB = 1, RW = 1)
  12. Strangalia famelica solitaria* – 2 (MB = 2, RW = 0)
  13. Typocerus velutinus* – 2 (MB = 1, RW = 1)
  14. Xylotrechus colonus* – 2 (MB = 0, RW = 2)
  15. Elytrimitatrix undatus – 1 (MB = 1, RW = 0)
  16. Strangalia sexnotata** – 1 (MB = 0, RW = 1)

* Not previously reported at fermenting baits in Missouri.
** Not previously reported from fermenting baits anywhere.

With regards to other insects, no attempt was made to quantify their occurrence or diversity, but a few interesting specimens were collected. Elateridae (click beetles) and other beetles were notable by their absence, in contrast to the great diversity recorded from by Champlain & Knull (1932). Flower scarabs were the exception, with two Euphoria inda and a moderate series of E. sepulchralis taken only in red wine traps. The most common non-beetle insects encountered were moths, flies, and stinging wasps, for which molasses/beer seemed to be much more attractive than red wine. The majority of the wasps were Vespidae, but a few large Crabronidae (one Sphecius speciosus and two Stizus brevipennis, I think) and at least two species of Pompiliidae were collected (see box 3 image above).

The diversity of longhorned beetles collected this season was undoubtedly influenced by habitat selection for trap placement (interface between dry, post-oak woodland and dolomite glade). Different habitats would likely yield different species, although prior experience seems to suggest that traps placed in open woodlands are more productive than those placed in dense forests. Recently thinned forests may have good potential due to an abundance of dead wood from thinning operations and trees stressed by sudden exposure to sunlight. Plans are currently underway to place traps (both molasses/beer and red wine) in a variety of wooded habitats during the 2016 season.


Champlain, A.B. & H. B. Kirk. 1926. Bait pan insects. Entomological News 37:288–291 [Biodiversity Heritage Library].

Champlain, A. B. & J. N. Knull.  1932. Fermenting bait traps for trapping Elateridae and Cerambycidae (Coleop.).  Entomological News 43(10):253–257.

Frost, S. W. 1937. New records from bait traps. (Dipt., Coleop., Corrodentia). Entomological News 48:201–202 [Biodiversity Heritage Library].

Frost, S. W. & H. Dietrich. 1929. Coleoptera taken from bait-traps. Annals of the Entomological Society of America 22(3):427–436 [abstract].

Guarnieri, F. G. 2009. A survey of longhorned beetles (Coleoptera: Cerambycidae) from Paw Paw, Morgan County, West Virginia. The Maryland Entomologist, 5(1):11–22 [pdf].

MacRae, T. C. 1994. Annotated checklist of the longhorned beetles (Coleoptera: Cerambycidae and Disteniidae) known to occur in Missouri. Insecta Mundi 7(4) (1993):223–252 [pdf].

MacRae, T. C. 2000. Review of the genus Purpuricenus Dejean (Coleoptera: Cerambycidae) in North America. The Pan-Pacific Entomologist 76:137–169 [pdf].

MacRae, T. C. & M. E. Rice. 2007. Distributional and biological observations on North American Cerambycidae (Coleoptera). The Coleopterists Bulletin 61(2):227–263 [pdf].

© Ted C. MacRae 2015

North America’s most “extreme” jewel beetle

When Chuck Bellamy passed away two years ago, he left behind a remarkable legacy of study on the family Buprestidae (jewel beetles) that includes not only his insect collection—surely one of the best in the world in terms of representation of genera and species in the family—but also his extensive library of primary literature. Both of these assets, built over a period of decades, are now housed in the California State Collection of Arthropods at the CDFA Plant Pest Diagnostics Laboratory in Sacramento, California. Chuck, however, was not just a jewel beetle collector and taxonomist—he was also a skilled photographer, focusing (pun intended) largely, though not exclusively, on his beloved jewel beetles. Digital cameras were still far in the future when Chuck began photographing these beetles, and as a result the bulk of his photographic legacy exists in the form of 35mm slides. I was the fortunate recipient of his slide collection, numbering in the thousands, and have been slowly scanning his slides into digital format with the goal to eventually make them available to the larger community of buprestid workers. Some of his best photos were published in a memorial issue of The Coleopterists Bulletin (2014, volume 68, number 1), and I featured a few additional photos in this post shortly before the publication of that issue. There remain slides, however, of many additional species, a large number of which surely represent the only field photographs of live adults. As I convert his slides to digital format, I hope to share some of the more interesting here.

For the first of these featured species, I can think of no better one than Lepismadora algodones. This tiny little jewel beetle is the only representative of the genus, which was not even known until 1986 when it was discovered by Mimi & Rob Velten in the Algodones Sand Hills of southeastern California. The species and genus were described the following year (Velten & Bellamy 1987), making Lepismadora the most recently discovered new genus of jewel beetle in the U.S. The recentness of its discovery is remarkable, since southern California in general and the Algodones Sand Dunes in particular were thought to have been relatively well collected at the time of the beetle’s discovery. Also remarkable is the distant relationship of this monotypic genus to any other North American species; its closest known relative being the genus Eudiadora—known only from Argentina (Bellamy 1991).

Lepismadora algodones

Lepismadora algodones Velten, in Velten & Bellamy, 1987 (Coleoptera: Buprestidae)

Even more remarkable, however, are its highly localized distribution and extreme habitat. The entire type series (one male holotype and 159 paratypes) and all individuals collected since its description have been found only in a single old canal on the west side of the Algodones dunes. Summer temperatures in the dunes routinely reach in excess of 110°F and are even higher in the depressed canal where the beetles are found. Astoundingly, the adults are active only during the hottest hours of the day (ca. 10 a.m. to 2 p.m.), during which time they can be found on the flowers and foliage of fanleaf crinklematTiquilia plicata (Boraginaceae). The reason for the beetle’s highly restricted distribution is a mystery, as the plant on which the beetles are found is rather widespread across the southwestern U.S. and northwestern Mexico. A final mystery is the still unknown larval host plant—it could be T. plicata, but it could just as likely be something completely different.

Algodones Dunes

Old canal on the west side of Algodones Sand Hills, type locality of Lepismadora algodones.

I moved to California a few years after the species was described and, of course, soon set out to find it for myself. I had driven to southern California from my home in Sacramento to meet the late Gayle Nelson (another important mentor of mine), who told me where to find the beetle and what the host plant looked like but also warned me about the extreme heat I would encounter. His advice was to hike the canal until I had half a bottle of water, then turn around and hike back. Mindful of his advice, I arrived at the dunes the next day around mid-morning, filled my water bottle and hydrated myself as much as I could, and climbed down into the canal. The heat was overpowering—more so down in the canal and far beyond anything I had ever experienced to that point, and after quickly recognizing the host plants I began tapping their tiny, prostrate branches over my beating sheet and looking for the beetles. I went as far as I could down the canal, perhaps 200 yards, before I had to turn around, but I had not yet seen any beetles and was starting to lose hope. I continued to tap host plants on the way back, though by then not really expecting to see anything. About halfway back I saw something laying on the ground a short distance ahead. As I approached I saw it was a small plastic vial with a white cap, and when I picked it up I saw inside a dried out T. plicata twig and a dead adult beetle—unmistakably L. algodones! While excited to have found the species, it was at the same time a bit unsatisfying for the specimen to be one that somebody else had collected before me and then lost (for all I know, it could have been Chuck Bellamy, considering that the beetle was apparently intended to be kept alive, possibly for photography!). I slipped the vial into my pocket, started tapping branches again, and found three additional adults in the immediate vicinity of where I had found the vial (and doing much to soothe my dissatisfaction with the first specimen). Those would be the only specimens that I would find that day, though I would succeed in finding another individual on a subsequent visit two years later.


Bellamy, C. L. 1991. A revision of the genus Eudiadora Obenberger (Coleoptera: Buprestidae). Proceedings of the Entomological Society of Washington 93(2):409-419 [Biodiversity Heritage Library].

Velten, R. K. & C. L. Bellamy. 1987. A new genus and species of Coroebini Bedel from southern California with a discussion of its relationships in the tribe (Coleoptera, Buprestidae). The Coleopterists Bulletin 41(1):185–192 [pdf].

© Ted C. MacRae 2015