Many thanks to Ted MacRae for introducing me to another stunner of a beetle. On more than one occasion Ted has taken me and others out to the field to find one of the strikingly beautiful and rare beetles that he knows so well. This time the treasure we sought was the jewel beetle, Dicerca pugionata (Buprestidae), also known as the Witch-hazel Borer. Witch-hazels (Hamamelis spp.) may be the preferred host plant but they are also found on alders (Alnus spp.) and ninebark (Physocarpus opulifolius). In this opportunity, we went to a specific patch of ninebark at Victoria Glades where Ted had found them previously.
After observing Vespula vulgaris foraging for the diaspores of Trillium ovatum in Oregon, Jules (1996) coined the term vespicochory to describe the dispersal of seed by Vespid wasps, specifically members of the Vespinae – the Vespidae subfamily that is comprised of yellowjackets and hornets. Few other descriptions have been recorded on observations of Vespinae acting as secondary seed dispersers in myrmecochorous plants. In controlled experiments, V. maculifrons has been reported to disperse T. cuneatum, T. undulatum and T. catesbaei in North Carolina and South Carolina (Zettler et al., 2001) and T. discolor in South Carolina (Bale et al., 2003). To my knowledge, this is the first recorded observation of the dispersal of T. recurvatum by Vespid wasps.
Before I begin describing my observations, I will first review and discuss the potential implications of Vespinae dispersal as an alternative to myrmecochory in trilliums. In most descriptions, myrmecochory has been described as a mutualist symbiose, meaning that both plant and ant species benefit from the relationship. Ants benefit by gaining the lipid and protein rich eliasome of the diaspore to feed their young while the plants benefit by having their seed dispersed from the parent plant and gain potential benefits in overwintering and germination environments. Similarly, for vespicochory to be considered as an important seed dispersal syndrome, we should consider the benefits to both sides and compare the role these wasps play to that of their ant cousins.
Yellowjackets, in addition to seizing seed directly from ants, removed more seeds (40%) from index cards than did each of three ant species observed (8 – 28%) (Bale et al., 2003). Zettler et al. (2001) measured dispersal distances by V. maculifrons and found an average distance of 1.4 m compared to a mean of 0.98 m in global cases of myrmecochory (Gómez and Espadaler, 1998). This difference in dispersal distance alone is significant; however, 53% of the seeds removed by V. maculifrons in this study were moved beyond 20 m – the furthest extent of their measuring capabilities, and were unrecovered, indicating a much higher than calculated average dispersal distance.
In addition to dispersal distance, another important thing when considering the benefits to the plant in a particular dispersal syndrome, is what is done with the diaspore once removed. The mandibles of Vespids are considerably larger and assumedly much more powerful than those of the ant species involved in dispersing trillium seed throughout their range. It is therefore a possibility that the seed could face catastrophic damage from the foraging wasp. Of the original seed recovered by Zettler et al. (2001), 95.7% had the eliasomes removed. Of these, 17% of the seeds had scarification near where the eliasome was attached but no seeds showed visible signs of embryo damage. The ultimate use of the eliasome was unknown in Zettler et al. (2001); however, Jules (1996) observed yellowjackets taking diaspores directly into their nest where, presumably, they were fed to developing young. Vespids typically nest underground and waste (i.e. seed portions of diaspores) are deposited below the nest. As mentioned by Zettler, “…we do not know how seed burial in these nests might affect seed germination and seedling emergence.” In cases where eliasomes are removed and seed are dropped randomly on the ground, it would be interesting to know how these seed fare in comparison to those buried within the nest. Further study is needed to determine the fate of seeds moved by these wasps when compared to myrmecochory.
The following observations and accompanying photographs were conducted at August G. Beckemeier Conservation Area in St. Louis County, Missouri. On August 5, 2021 at ~ 18:00 hrs., I collected a ripe fruit of T. recurvatum and placed it with about 25% of the seed exposed within 20 cm of a nest of Formica pallidefulva ants. My goal was to observe and photograph the ants carrying away the diaspores. The ants found the fruit within minutes and quickly began moving the loosely separated diaspores. After approximately 10 minutes the first V. maculifrons found the fruit and quickly left with a diaspore. It returned alone five times with gaps ranging between approximately one and three minutes. After the fifth visit, two to four wasps were at the scene at any given time, each working to free seeds from the fruit until all seeds were removed. I found that the wasps were able to pull the diaspores free from the fruit capsule matrix much easier than the ants. The ants tried, at times, to defend the fruit and the wasps did give them a wide berth. When two or more wasps were on the fruit at one time, however, the ants were ineffectual in their defense.
I was not setup to make accurate counts or to try and make seed dispersal distance measurements. It appeared the wasps moved at least 75% of the seed while F. pallidefulva moved the remaining into their nest. I believe this discrepancy was primarily due to the ability of the wasps to excise the diaspores from the fruit capsule matrix more quickly and easily than the ants. I watched one wasp perched on a short sapling approximately 1.5 m from the fruit. It removed the eliasome, letting the seed fall to the leaf litter below and then left carrying the eliasome with it.
These images were taken using a full-sized sensor digital camera and a 180mm macro lens with a 1.4x teleconverter and 30 mm extension tube stacked between the lens and camera body. This combination of equipment provides quite a long focusing distance, ensuring the photographer does not disturb the subjects. An off-the-body external speedlight “flash” was used at varying levels of power to obtain the extra light needed. Most of these images were taken at f/16, 1/100 sec. and ISO-640 and were taken handheld while using a fallen log for additional support.
This was an anecdotal observation of a single occurrence of vespicochory. This is a subject that warrants further investigation. Could vespicochory be just as or even more important in the dispersal and emergence of some “myrmecochorous” plants as myrmecochory? It would be interesting to know more about the frequency and dynamics of this unique seed dispersal mechanism.
- Bale, M.T., J. A. Zettler, B.A. Robinson, T. P. Spira, & C.R. Allen. 2003. Yellow jackets may be an underestimated component of ant-seed mutualism. Southeastern Naturalist 2(4):609-614.
- Gómez, C. & X. Espader. 1998. Myrmecochorous dispersal distances: a world survey. Journal of Biogeography 25:573-580.
- Jules, E.S. 1996. Yellow jackets (Vespula vulgaris) as a second seed disperser for the myrmecochorous plant, Trillium ovatum. American Midland Naturalist 135(2):367-369.
- Zettler, J.A., T.P. Spira, C.R. Allen. 2001. Yellow jackets (Vespula spp.) disperse trillium (spp.) seeds in eastern North America. American Midland Naturalist 146(2):444-446.
A little late for a Halloween post, my apologies, but I wanted to share what is probably the best-preserved example of a Gibellula-infected spider I have found to date. Gibellula is a genus of endoparasitic Cordyceps fungi that primarily infect spiders. Although the nicely preserved jumping spider (Salticidae) and the fruiting branches of the fungus is what grabs the eye, it wasn’t until I finished processing the photos that a question came to mind for me.
See the white fibers that surround the spider? I see two possible options for the origin of these. First, I should explain a little of what I have read about the life history of these parasitic fungi. Similar to the Cordyceps that infect insects, Gibellula-infected spiders become “zombies” and will typically position themselves on the undersides of leaves, as the one pictured here was found. Here the fungus finally kills its host and sends out spores that are now nicely positioned to fall upon potential new spider hosts. Back to that bed of white threads. I see one function and two possible origin ideas of these. I believe the function of these is to keep the spider anchored to the leaf so that it does not fall to the ground and greatly hinder the ability of the fungi to infect new hosts. For the potential origin, these could be mycelia of the infecting fungus, or, even better, these could be silk created by the spider, induced by the fungus to anchor itself as the last act before its death.
If you have other ideas as to the potential origin or function of this bead of threads, please let me know!
One of two Buprestidae family members I was fortunate to photograph this year. This guy was found at Bush Wildlife Conservation Area in St. Charles County, MO on 01/AUG/21.
All three of the Salvia azurea I planted in the front bed did very well this year and even played host to an equally gorgeous moth, Pyrausta inornatalis.
Our neighborhood Chimney Swifts have pretty much headed south and will be missed until they come again in the spring. This reminds me of a some birds that Casey and I ran into at a location we camped at in Arkansas this spring. They were using a secluded and dark hallway that lead to bathrooms we used for their overnight roosting. This was the first time I have been so close to perched Chimney Swifts so I had to take a few pics.
This southern black widow was found at Sand Prairie Conservation Area in Scott County MO. Quite unusually, she had built a web in the open within the tallest branches of a Polygonum americanum (American jointweed), where she had just dispatched a Dielis plumipes (Feather-legged Scoliid Wasp).
For the past few years I have noticed a good number of native bee nest holes along exposed sections of bare soil at one of my favorite hiking and nature observation sites – August G. Beckemeier Conservation Area in St. Louis Co., MO. This past spring I finally decided to make this a project and set about a quest to make some images of these gals provisioning their nests. As usual, I wound up learning along the way.
As is commonly known, many of our native bees are solitary and nest without close contact or cooperation in regards to conspecifics. At the opposite side of this spectrum of sociality in the Hymenoptera are most species of bumble bees and the honeybee. These bees are considered truly social, or, eusocial. The characteristics necessary to be considered a eusocial species are 1) cooperative care of offspring of others within the colony, 2) overlapping generations within a colony of adults, and 3) a division of labor into reproductive and non-reproductive groups. Many of our bee species lie somewhere between these two extremes. The bee of focus here, Agapostemon virescens, lies early in the area we call being presocial, aka parasocial.
Let’s clarify the differences between a presocial species such as A. virescens and the eusocial honeybee. The honeybee shows all three necessary characteristics of a eusocial species. The individual workers obviously care for brood that are not their own – they don’t even have offspring of their own, instead spending much of their lives caring for the offspring of their queen (sisters). They have multiple overlapping generations within the hive in a particular season, as well as across multiple seasons and as just mentioned, there is a division of labor into reproductive and non-reproductive castes. A. virescens on the other hand, is not nearly as cooperative. Individuals of this species share basically just a front door to their brood chambers and nothing more. After entering the communal nest, each female builds their own brood sub-chamber cells and each provisions their own by processing pollen into cakes and leaving them in their respective brood chambers. There is no brood care after the egg is deposited and the sub-chamber sealed. The offspring then emerges later in the summer.
So, what are the pre-conditions necessary for the eventual development of more complicated forms of sociality, i.e. eusociality? Or more directly, what advantages are there in adopting more of a social lifestyle if we assume the starting point was a solitary existence? Scientists consider two important pre-conditions need be met for the evolution of eusociality. First, the species offspring must be altricial, or require a great amount of parental care in order to reach maturity. Second, there need be low reproductive success rates of solitary pairs that attempt to reproduce. Here is what is believed to be the primary driver that pushed A. virescens into this presocial condition.
Kleptoparasitism is where one animal takes advantage of the hard work of another by taking their prey or collected foods. In this case, we are primarily concerned with the large group of bees known as cuckoo bees. Kleptoparasitism has evolved numerous times in the Hymenoptera and cuckoo bees lay their egg on or near the host’s provisions. The parasite will hatch first and eat the host’s pollen and will often kill and eat the host’s larvae as well. With such an obviously successful reproductive strategy, it should come as no surprise that there would be a strong selective advantage of finding ways to thwart these parasites. In the case of A. virescens, evidence suggests that by communal living as described here, the rate of kleptoparasitism is much lower when compared to related species that have the completely solitary reproductive strategy.
I guess the obvious next question is how in the world could eusociality evolve from this state? This is a fascinating story that involves terms like kin selection, altruism and haplodiploidy. It also involves a good deal of math and explanation from some of the greatest evolutionary thinkers since the time of Darwin (read anything by William D. Hamilton for example). It is also well out of the scope of this piece. But, I hope it is clear that before getting near the high rung of eusociality on this ladder, that a small first step like seen in this example would be necessary.
I hope I got most of this correct enough. It’s been a long time since I took Zuleyma Tang-Martinez’s Evolution of Animal Sociality class at University, which I thoroughly enjoyed. Please feel free to leave a comment to correct or clarify or ask a question.
Much of what I covered here and a lot more can be found in Malte Andersson’s The evolution of eusociality (Ann. Rev. Ecol. Syst. 1984. 15:165-89
The evolution of Eusociality
Back in mid-June I discovered a number of Synchlora aerata (camouflaged looper, wavy-lined emerald moth) that were using our coreopsis as host. Not only are these spectacular adult moths in the family Geometridae, but they are obviously special while in the larval phase as well. These caterpillars are known for attaching bits and pieces of the plant tissues they feed on (often flower petals) to their backs as means of camouflaging against their predators.