Estimation of population sizes and species ranges is central to population and conservation biology. It is widely appreciated that imperfect detection of mobile animals must be accounted for when estimating population size from presence–absence data. Sessile organisms also are imperfectly detected, but correction for detection probability in estimating their population sizes is rare. We illustrate challenges of detection probability and population estimation of sessile organisms using censuses of red wood ant (Formica rufa‐group) nests as a case study. These ants, widespread in the northern hemisphere, can make large (up to 2 m tall), highly visible nests. Using data from a mapping campaign by eight observers with varying experience of sixteen 3600‐m² plots in the Black Forest region of southwest Germany, we compared three different statistical approaches (a nest‐level data‐augmentation patch‐occupancy model with event‐specific covariates; a plot‐level Bayesian and maximum‐likelihood model; nonparametric Chao‐type estimators) for quantifying detection probability of sessile organisms. Detection probabilities by individual observers of red wood ant nests ranged from 0.31 to 0.64 for small nests, depending on observer experience and nest size (detection rates were approximately 0.17 higher for large nests), but not on habitat characteristics (forest type, local vegetation). Robust estimation of population density of sessile organisms—even highly apparent ones such as red wood ant nests—thus requires estimation of detection probability, just as it does when estimating population density of rare or cryptic species. Our models additionally provide approaches to calculate the number of observers needed for a required level of accuracy. Estimating detection probability is vital not only when censuses are conducted by experts, but also when citizen‐scientists are engaged in mapping and monitoring of both common and rare species.

In a 1.140 km² study area of the volcanic West Eifel, a comprehensive investigation established the correlation between red wood ant mound (RWA; Formica rufa-group) sites and active tectonic faults. The current stress field with a NW-SE-trending main stress direction opens pathways for geogenic gases and potential magmas following the same orientation. At the same time, Variscan and Mesozoic fault zones are reactivated. The results showed linear alignments and clusters of approx. 3,000 RWA mounds. While linear mound distribution correlate with strike-slip fault systems documented by quartz and ore veins and fault planes with slickensides, the clusters represent crosscut zones of dominant fault systems. Latter can be correlated with voids caused by crustal block rotation. Gas analyses from soil air, mineral springs and mofettes (CO₂, Helium, Radon and H₂S) reveal limiting concentrations for the spatial distribution of mounds and colonization. Striking is further the almost complete absence of RWA mounds in the core area of the Quaternary volcanic field. A possible cause can be found in occasionally occurring H₂S in the fault systems, which is toxic at miniscule concentrations to the ants. Viewed overall, there is a strong relationship between RWA mounds and active tectonics in the West Eifel.

Short-term earthquake predictions with an advance warning of several hours or days are currently not possible due to both incomplete understanding of the complex tectonic processes and inadequate observations. Abnormal animal behaviors before earthquakes have been reported previously, but create problems in monitoring and reliability. The situation is different with red wood ants (RWA; Formica rufa-group (Hymenoptera: Formicidae)). They have stationary mounds on tectonically active, gas-bearing fault systems. These faults may be potential earthquake areas. For three years (2009–2012), two red wood ant mounds (Formica rufa-group), located at the seismically active Neuwied Basin (Eifel, Germany), have been monitored 24/7 by high-resolution cameras with both a color and an infrared sensor. Early results show that ants have a well-identifiable standard daily routine. Correlation with local seismic events suggests changes in the ants’ behavior hours before the earthquake: the nocturnal rest phase and daily activity are suppressed, and standard daily routine does not resume until the next day. At present, an automated image evaluation routine is being applied to the more than 45,000 hours of video streams. Based on this automated approach, a statistical analysis of the ants’ behavior will be carried out. In addition, other parameters (climate, geotectonic and biological), which may influence behavior, will be included in the analysis.

We measured methane (CH₄) and stable carbon isotope of methane (δ¹³C-CH₄) concentrations in ambient air and within a red wood-ant (RWA; Formica polyctena) nest in the Neuwied Basin (Germany) using high-resolution in-situ sampling to detect microbial, thermogenic, and abiotic fault-related micro-seepage of CH₄. Methane degassing from RWA nests was not synchronized with earth tides, nor was it influenced by micro-earthquake degassing or concomitantly measured RWA activity. Two δ¹³C-CH₄ signatures were identified in nest gas: −69‰ and −37‰. The lower peak was attributed to microbial decomposition of organic matter within the RWA nest, in line with previous observations that RWA nests are hot-spots of microbial CH₄. The higher peak has not been reported in previous studies. We attribute this peak to fault-related CH₄ emissions moving via fault networks into the RWA nest, which could originate either from thermogenic or abiotic CH₄ formation. Sources of these micro-seepages could be Devonian schists, iron-bearing “Klerf Schichten”, or overlapping micro-seepage of magmatic CH₄ from the Eifel plume. Given the abundance of RWA nests on the landscape, their role as sources of microbial CH₄ and biological indicators for abiotically-derived CH₄ should be included in estimation of methane emissions that are contributing to climatic change.

Ecological studies often are subjected to unintentional biases, suggesting that improved research designs for hypothesis testing should be used. Double-blind ecological studies are rare but necessary to minimize sampling biases and omission errors, and improve the reliability of research. We used a double-blind design to evaluate associations between nests of red wood ants (Formica rufa, RWA) and the distribution of tectonic faults. We randomly sampled two regions in western Denmark to map the spatial distribution of RWA nests. We then calculated nest proximity to the nearest active tectonic faults. Red wood ant nests were eight times more likely to be found within 60 m of known tectonic faults than were random points in the same region but without nests. This pattern paralleled the directionality of the fault system, with NNE–SSW faults having the strongest associations with RWA nests. The nest locations were collected without knowledge of the spatial distribution of active faults thus we are confident that the results are neither biased nor artefactual. This example highlights the benefits of double-blind designs in reducing sampling biases, testing controversial hypotheses, and increasing the reliability of the conclusions of research.