The question matters because dung-eating insects perform an ecological service that modern agriculture quietly depends on. Coprophagous beetle and fly larvae decompose vertebrate dung, recycling nutrients back into managed grasslands and preventing pastures from being buried under accumulating excrement. The importance of this service became vividly clear when cattle were introduced to Australia, where no co-evolved dung fauna existed to break down the proliferating pats. Dung beetles from southern Europe had to be imported deliberately to control the problem. Understanding whether a given decomposer is locked onto one dung type or can exploit many therefore has direct consequences for how nutrient cycling works across agricultural landscapes.

The theory of niche differentiation predicts that species sharing a habitat should differentiate with regard to their key resources, notably food, with physiological adaptations driving specialization over evolutionary time. Yet in nature, many coprophagous insects coexist on roughly the same resource, forming a continuum from extreme specialists that exploit only a single vertebrate’s dung to broad generalists that thrive on whatever they find. Because the nutritional components of dung, from fibrous plant matter to the bacteria and fungi growing within it, may be broadly similar depending on whether the producer is a herbivore, carnivore, or omnivore, researchers had long hypothesized that dung feeders should tend toward generalism rather than extreme specialization. That hypothesis, however, had never been systematically tested for yellow dung fly larvae, whose success on diverse dung types remained an open question despite decades of intensive study of the species’ mating behavior.

The yellow dung fly is an unusual insect in several respects. Approaching the size of a honey bee, it is among the largest and most abundant dung decomposers in cold-temperate regions across the entire northern hemisphere. Unlike most insects, which favor warmth, this fly actually prefers cooler climates, having invaded arctic regions of both the Old and New Worlds and colonized high-altitude habitats such as the Alps. In Switzerland, where cows for milk, cheese, and beef production range from lowland farms to alpine pastures beyond the treeline, the species is essentially omnipresent. Females lay their eggs into fresh vertebrate dung, which the larvae consume and recycle before pupating in the soil nearby. Adults sip nectar for energy but also require small insect prey to reproduce, a nutritional strategy known as anautogeny, and mating takes place around the fresh dung pat, where males abound to intercept incoming females.

To test whether this fly is truly a cow dung specialist, the research team raised yellow dung fly larvae on dung from four large mammals common in Switzerland: domesticated cow and horse, both herbivores, and wild boar, an omnivore, and wild red deer, another herbivore. Cow and horse dung was collected from farms near Zürich, wild boar dung from Wildpark Langenberg, and red deer dung from Tierpark Goldau. In every case, freshly collected dung from many individuals was mixed thoroughly and frozen at minus 80 degrees Celsius for at least two weeks to kill all arthropods within it, ensuring that any differences in larval performance reflected dung quality rather than the presence of other dung inhabitants. The flies themselves came from a laboratory stock originally caught in Fehraltorf, Switzerland, and maintained on defrosted cow dung for several generations.

The experimental design was carefully controlled. Single-held females were allowed to copulate with a random male in glass vials containing water, sugar, and Drosophila prey, and then laid egg clutches into a smear of cow dung on filter paper. Using a split-brood design, the researchers transferred typically ten eggs from each clutch into small plastic containers with overabundant dung of one of the four types, more than two grams per egg, so that food quantity was never limiting. The containers were placed in a climate chamber set at 19 degrees Celsius, 60 percent relative humidity, and a 13-hour light period. The team then scored survivorship as the proportion of individuals that emerged as adults, recorded sex-specific egg-to-adult development time, and measured hind tibia length as a reliable index of final structural body size, calculating growth rate as tibia length divided by development time in days.

The results were striking in their consistency. Larva-to-adult survival did not vary significantly among the four dung types, hovering around an overall mean of 80 percent, a value typical for cow dung in long-term laboratory studies. Survival was somewhat lower in boar dung, at roughly 73 percent, and somewhat higher in red deer dung, at roughly 93 percent, but the planned comparison between domestic and wild mammal dung showed no overall difference. Development time, body size, and growth rate did vary somewhat among dung types, with development longest in cow dung yet producing the largest adults, while growth rate was fastest in wild boar dung but yielded relatively small flies. The researchers judged this variation minor relative to that typically induced by other environmental stressors such as dung limitation, heat, and drought, and importantly, not in accordance with the main hypotheses being tested.

The finer-scale differences in performance most likely reflect variation in dung consistency, water content, and the nutritional value of the dung microbiome of the different mammals. Previous estimates showed that cow dung contains about 81 percent water, horse dung about 77 percent, red deer dung about 69 percent, and wild boar dung about 71 percent, differences that likely affect the ability of larvae to move through and digest their food. The researchers also noted that the significant sex-by-dung type interactions observed across all performance variables mainly reflect size scaling in this strongly sexually dimorphic species, in which males are larger, rather than differential physiological responses to the food source. A next step, they suggest, would be testing oviposition preferences of gravid females in choice experiments, which should correlate with the performance ranking revealed by the life history traits measured here.

The broader implication is that yellow dung flies are opportunistic in their choice of dung, reproducing on deer or boar dung when in the forest and switching readily to cow, horse, or sheep dung when in grasslands, depending on site and weather. In Swiss lowland pastures interspersed with agricultural areas and forests, more alternative livestock substrates are available than in highland grasslands, while in the Alps, where cows and sheep abound up to the treeline, wild animal dung from deer, ibex, and mountain goats becomes relatively more abundant, again permitting easy switching between dung types. Because the species is cold-adapted in general, longer winters in the Alps shorten the growing season and extend winter diapause of pupae but should not strongly reduce fly mortality or population density.

The study concludes that yellow dung flies can reproduce successfully on multiple types of mammal dung, wild or domestic, herbivore or omnivore, and likely also carnivore, with reproductive fitness that does not strongly deviate from that observed in cattle dung. The species is widespread, the researchers argue, because it could plastically shift to the dung of common herbivorous livestock after domestication without losing the ability to reproduce on the dung of common wild mammals. In this respect, the yellow dung fly belongs to the minority of insect taxa that benefit from humanity’s agricultural activities rather than suffering from them, and is therefore not of special conservation concern. Far from being a domesticated cow dung specialist, this familiar pasture fly turns out to be an evolutionary opportunist that simply followed livestock around the world while keeping its options open.

Subject of Research: Ecology and evolutionary biology of dung-feeding insects

Article Title: Are yellow dung flies domesticated cow dung specialists?

Article References: Blanckenhorn, W. U., & Burkhard, D. (2023). Are yellow dung flies domesticated cow dung specialists?. Alpine Entomology, 7, 135-141. https://doi.org/10.3897/alpento.7.107649

Image Credits: AI Generated

DOI: 10.3897/alpento.7.107649

Keywords: yellow dung fly, dung decomposition, niche differentiation, coprophagous insects, livestock pastures, Switzerland, Scathophaga stercoraria, dung generalists, entomology, life history traits, yellow, dung

The Ponto-Caspian region, which encompasses the Black, Azov, Caspian, and Aral Sea basins, is one of the most prolific sources of aquatic invasive species in Europe and North America. Among its exports are the corophiids, small tube-dwelling filter feeders that have been spreading across the continent since the early twentieth century. Chelicorophium curvispinum was the first to reach Western Europe, traveling from Poland through the central corridor. C. robustum and C. sowinskyi followed, their spread accelerated by the opening of the Main-Danube canal in the 1990s. Now a fourth species, C. maeoticum, has arrived in the Netherlands, likely carried directly by sea freighters rather than through the interconnected inland waterways.

What makes the arrival of C. maeoticum so surprising is that it was never considered a serious invasion risk. Within its native range it is apparently rare compared to the three already invasive species, and its distribution in the River Danube basin actually narrowed during the twentieth century. Yet since its discovery in the Netherlands in 2021, it has colonized all major stretches of the Rhine system, large lakes such as Ijsselmeer and Markermeer, and the inland canal network. Understanding how it manages to establish itself alongside three close relatives is central to predicting what happens next.

Corophiids are sedentary animals that live in self-constructed tubes in the sediment or among stones. They feed by filtering particles from the water, and the crucial trait determining what they can eat is the mesh size of their filtering screen, formed by bristled setae on their second gnathopods. The distance between the bristles sets the size of food particles each species can capture, and previous studies have shown that coexisting corophiids tend to divide the food particle size spectrum into three partitions. With four invasive species now sharing the Rhine, the question was whether there is enough room on this niche axis for all of them.

The research team measured filter mesh sizes in specimens collected from the estuarine section of the River Rhine and the Rhine Delta in April 2024, using a variety of sampling methods including box corers, Van Veen grabs, and even a handheld vacuum cleaner on littoral stones. For comparison, they also analyzed a historic sample from the River Tisza in Hungary, dating from September and October 1943, in which C. maeoticum co-occurred only with C. sowinskyi before apparently disappearing from the river. The museum specimens, stored in the Hungarian Natural History Museum, were carefully dissected to expose the filtering setae, which were photographed under a light microscope and measured in ImageJ2.

The results revealed a densely packed niche space. Mean filter mesh sizes in the Dutch material ranged from 1.71 to 5.45 micrometers across the four species. C. maeoticum showed an intermediate interval of 2.31 to 3.63 micrometers, partially overlapping with the range of C. sowinskyi, which measured between 1.71 and 3.01 micrometers. C. curvispinum and C. robustum had the largest mesh sizes, between 3.45 and 5.26 and between 3.58 and 5.45 micrometers respectively, largely overlapping with each other. Statistical modelling confirmed significant differences between all species pairs except C. curvispinum and C. robustum, whose filter mesh sizes were almost completely indistinguishable.

The strongest niche overlap was between C. maeoticum and C. sowinskyi. The estimated mean difference of 0.7 micrometers between the two species in the Rhine is considerably smaller than the 1.58 micrometers measured in the historic Tisza sample, where the two species showed no overlap at all. This is the first time an overlap has been reported for C. sowinskyi with any other species, suggesting that differentiation by food particle size alone may not guarantee stable coexistence between the newcomer and the earlier colonist. By contrast, the differences between C. maeoticum and C. curvispinum or C. robustum were comparable to the differentiation observed among the three invasive species in the Lower Danube.

Looking for additional mechanisms, the researchers turned to the second antennae, appendages known from related species to play roles in both aggressive encounters and deposit feeding. In the mudflat corophiid Corophium volutator, males fight each other over females using their enlarged second antennae, and the same appendages are used to scrape the sediment surface around burrow openings. The team measured the relative lengths and widths of the second antennae in adult specimens of all four invasive species, in both males and females, using log-log transformed data and linear models. The results showed marked interspecific differences, particularly in antenna width in females, where all species pairs differed significantly. C. maeoticum and C. robustum had considerably thicker second antennae than C. curvispinum and C. sowinskyi in both sexes.

These morphological differences hint at a competitive hierarchy. Because crevice size limits the body size of occupants in corophiid microhabitats, success in territorial combat may depend more on antenna properties than on overall body size. The researchers hypothesize that C. maeoticum and C. robustum, with their more robust appendages, are dominant in interference competition, while the gracile C. curvispinum and C. sowinskyi can invest more in somatic growth and reproduction. Remarkably, the latter two species have been more successful at colonizing new areas, while the thicker-antennaed species could establish themselves in habitats already occupied by their congeners. A similar pattern appears in Dikerogammarus amphipods, where the faster-spreading D. haemobaphes is often replaced by the more robust and competitively superior D. villosus.

Body size adds yet another dimension. The maximal body lengths in the studied material were 5, 6.4, 6.5, and 8.1 millimeters for C. maeoticum, C. sowinskyi, C. curvispinum, and C. robustum respectively, producing body length ratios remarkably close to 1.3. This figure echoes Hutchinson’s classic rule, which holds that a minimal size difference of about 1.3 is often necessary for coexistence among guild members. While the generality of this rule is debated, body size differences can contribute to niche differentiation through variations in life history, microhabitat use, or predation risk. Taken together, filter mesh size, body length, and the relative width of the second antennae appear to act as proxies of independent niche axes, with the species showing non-random associations that minimize overall niche overlap. The authors suggest that these combined differences are likely to allow the coexistence of all four species and portend the continued spread of C. maeoticum through the interconnected waterways of Western and Central Europe, in stark contrast with its mysterious decline in the Danube catchment. More studies are needed to reveal the full range of behaviors these peculiar appendages are involved in and how their morphological features determine their functionality, but the study provides a novel perspective on the ecological interactions of invasive species beyond simple food resource partitioning.

Subject of Research: Ecological niche differentiation among invasive Ponto-Caspian corophiid amphipods in the River Rhine

Article Title: Differences in antennal morphology and body size might offset increased overlap in food particle size among invasive Ponto-Caspian corophiids ( Crustacea , Amphipoda )

Article References: Borza, P., Achterkamp, B., & van Haaren, T. (2026). Differences in antennal morphology and body size might offset increased overlap in food particle size among invasive Ponto-Caspian corophiids (Crustacea, Amphipoda). NeoBiota, 107, 21-34. https://doi.org/10.3897/neobiota.107.181767

Image Credits: AI Generated

DOI: 10.3897/neobiota.107.181767

Keywords: invasive species, Ponto-Caspian, amphipods, corophiids, River Rhine, niche differentiation, filter feeding, antennal morphology, ecology, freshwater biology, Differences, antennal

The research, led by Hongjae Park and Suhyun Kim of Inha University together with colleagues including senior author Jang-Cheon Cho, is notable less for any single discovery than for its sheer temporal reach. Most microbial ecology studies capture a snapshot: a season here, a bloom there. Short-term surveys, the authors argue, fundamentally miss the ecological trajectories that matter, because microbial communities are shaped by processes that unfold across years, not weeks. By collecting samples every month for five consecutive years and pairing them with detailed environmental measurements, the team could separate the recurring signal from the noise, distinguishing microbes that return like clockwork from those that seize fleeting opportunities.

The analysis identified six distinct clusters of seasonally recurring microbes, each rising and falling in a coordinated annual rhythm. Together, these clusters drive what the researchers describe as a predictable microbial year, a succession that repeats with enough fidelity to serve as a baseline against which future disruptions could be measured. This kind of temporal structure has long been suspected in freshwater systems, but demonstrating it with monthly resolution over half a decade gives the pattern a weight that shorter studies could not provide. The annual cycle, the study shows, operates alongside a parallel cast of episodic populations that transiently occupy ephemeral niches, appearing when conditions briefly favor them and receding just as quickly.

Among the most striking results is the ecological versatility of the acI and acIV clades of Actinomycetota, a group of streamlined bacteria that dominate many freshwater systems. These organisms carry some of the smallest genomes known among free-living bacteria, a trait called genome streamlining that has traditionally been associated with highly specialized, static lifestyles. Yet the Lake Soyang data revealed extensive spatiotemporal niche differentiation within these clades. Recurring lineages partitioned into subgroups associated with low-oxygen conditions and with winter, niches that had not previously been described for these organisms. In other words, even the most minimal genomes in the lake are not ecological generalists or specialists in any simple sense; they are a finely subdivided collection of lineages, each tuned to a particular slice of the lake’s seasonal and vertical structure.

The study also found that specific members of these clades can behave as episodic bloomers, erupting in abundance when circumstances align and then fading back into the background. This dual identity, recurring yet occasionally explosive, expands the known ecological repertoire of the Actinomycetota and complicates the tidy assumption that genome size predicts ecological strategy. A bacterium with a stripped-down genome, it turns out, can still be a flexible opportunist when the moment is right, and the five-year record was long enough to catch those moments in the act.

To understand how these populations relate to one another, the team turned to network analysis, a computational approach that maps statistical associations between microbes across time. The resulting network revealed dense interconnectivity among diverse populations, a pattern the authors interpret as evidence of finely coordinated, time-dependent succession. Rather than a loose assembly of independent species responding separately to temperature and nutrients, the lake’s microbiome behaves more like an ensemble, with the rise of one group paving the way for the next in a sequence that repeats year after year. Such coordination suggests that ecological interactions, whether competition, cross-feeding, or shared vulnerability to grazers and viruses, weave the community into a tightly coupled system.

Why does this matter beyond the boundaries of one Korean reservoir? Freshwater ecosystems supply drinking water, support fisheries, and regulate nutrient flows to the ocean, and microbes sit at the center of all of these functions. They cycle carbon and nitrogen, determine water clarity, and can signal trouble long before it becomes visible, as when cyanobacterial blooms transform a reservoir into a toxic soup. Oligotrophic lakes like Soyang are generally considered resilient because their low nutrient loads limit runaway growth, but climate change, land-use shifts, and warming waters are testing that resilience worldwide. A documented five-year baseline of normal microbial behavior provides exactly the reference point managers need to detect when a system begins to drift.

The study’s authors emphasize this applied dimension directly. By linking short-term fluctuations to multiyear trends, they argue, long-term monitoring transforms microbial data from an academic curiosity into a practical management tool. Microbial indicators, the community compositions and seasonal signatures documented in the study, could be incorporated into freshwater monitoring programs, offering earlier and more sensitive warnings of eutrophication, oxygen depletion, or other stressors than conventional chemical and physical measurements alone. The work thus positions the lake’s smallest inhabitants as sentinels for the health of the whole ecosystem.

The technical achievement underlying these conclusions is considerable. Monthly sampling over five years demands sustained funding, meticulous sample handling, and the computational capacity to process hundreds of microbial community profiles alongside environmental variables such as temperature, oxygen, and nutrient concentrations. Disentangling recurring seasonal clusters from episodic bloomers requires statistical methods capable of recognizing both periodicity and one-off events, and the niche differentiation within the acI and acIV clades only became visible because the dataset was deep enough to resolve subgroups tied to specific depths, oxygen levels, and winter conditions. The study, supported by the National Research Foundation of Korea, stands as a demonstration of what patient, long-term observation can accomplish in a field often dominated by short campaigns.

For microbial ecologists, the message is that freshwater communities are neither chaotic nor static: they are structured by an annual clock that can be read and predicted, overlaid with episodic surprises that keep the system dynamic. For water managers, the message is that the microbes themselves can serve as instruments, recording environmental change with a sensitivity that no sensor can match. And for anyone who has looked out over a still lake and assumed nothing much was happening below, the study is a reminder that one of nature’s most intricate seasonal dramas plays out continuously in a single drop of water, repeating itself year after year with a precision that only five years of watching could reveal.

Subject of Research: Long-term microbial community dynamics and seasonal succession in the oligotrophic freshwater Lake Soyang, South Korea

Article Title: A Five-Year Time Series Reveals Recurrent and Episodic Microbial Community Dynamics in an Oligotrophic Lake

Article References: Park, H., Kim, S., Park, M. S., Kang, I., & Cho, J.-C. (2026). A Five-Year Time Series Reveals Recurrent and Episodic Microbial Community Dynamics in an Oligotrophic Lake. Microbial Ecology. https://doi.org/10.1007/s00248-026-02882-4

Image Credits: AI Generated

DOI: 10.1007/s00248-026-02882-4

Keywords: microbial ecology, freshwater ecosystem, oligotrophic lake, seasonal dynamics, Actinomycetota, acI clade, acIV clade, niche differentiation, time series, Lake Soyang, network analysis, water management