Researchers at the University of Liverpool, working with Richard Wall of the University of Bristol, carried out an extraordinarily intensive sampling campaign at Lyme Park in northern England. Every month from January to December 2022, the team dragged a fabric blanket across fixed transects at four-hour intervals, completing full 24-hour sampling cycles. This design allowed them, for the first time, to separate seasonal variation in tick activity from daily, or diel, variation, two dimensions of behaviour that previous studies had almost always examined in isolation. Because the sampling rounds captured ticks actively questing, that is, climbing vegetation with outstretched forelegs to ambush passing hosts, the counts represent genuine host-seeking behaviour rather than simple abundance.

The headline finding is that questing activity in I. ricinus is predominantly nocturnal. Densities of host-seeking ticks were highest during the dark hours of the sampling cycle, and statistical modelling confirmed that darkness itself was a positive predictor of the number of questing nymphs. This is a striking departure from the popular image of ticks as creatures that latch onto walkers in broad daylight, and it has immediate implications for how people, pets and wildlife encounter infected ticks in the field.

The second major moderator of activity was atmospheric moisture, captured by a single, elegant variable known as the saturation deficit. Saturation deficit combines air temperature and relative humidity into a measure of how strongly the air draws water from living tissue, and it is widely used by entomologists to describe desiccation stress in small terrestrial arthropods. Because ticks lack efficient water-conservation mechanisms and must periodically rehydrate within the humid microclimate of the soil and leaf litter, high saturation deficit effectively forces them off the vegetation and into protective refuges. In the new study, the density of questing nymphs was negatively associated with saturation deficit, meaning that hot, dry conditions suppressed host-seeking even when the season was otherwise favourable.

Crucially, the researchers showed that the strength of the nocturnal activity pattern itself varied with the seasonal moisture environment. Night-time questing was most evident in nymphs during months with high saturation deficit, when daytime conditions were too punishing for ticks to remain exposed. In cooler or wetter periods, when desiccation stress was lower, activity was distributed more evenly across the day. In other words, darkness does not simply switch ticks on; rather, harsh daytime climates push their activity into the night, and benign climates allow it to spread out. This interaction between the daily light cycle and seasonal moisture availability had not previously been demonstrated under natural field conditions for this species.

To untangle these effects, the team analysed their 24-hour, year-round dataset using Generalised Linear Mixed Modelling, a statistical framework well suited to count data with repeated measures. Mixed models allowed the investigators to account for the structure of the design, in which the same transects were sampled month after month at identical clock times, while testing the independent contributions of darkness, temperature, humidity and saturation deficit to tick density. The modelling confirmed that the negative effect of saturation deficit and the positive effect of darkness on questing nymph density were robust after controlling for the sampling structure, giving confidence that the observed rhythms reflect biology rather than artefacts of the schedule.

The seasonal dimension of the results was broadly reassuring for the field. The annual pattern of activity, with questing peaking in the warmer months and collapsing through winter, was largely consistent with previously published data on European tick phenology. Larvae, nymphs and adults each showed characteristic seasonal windows of host-seeking, reflecting the developmental timing that determines which life stages pose a threat at any given time of year. Nymphs, the stage most often implicated in transmitting Borrelia bacteria and tick-borne encephalitis virus to humans, dominated the datasets in the ways that surveillance specialists have come to expect.

What makes the study transformative is not the seasonal story but the daily one. Diel patterns in tick behaviour have been chronically understudied, largely because most tick surveillance is conducted during working hours, typically between mid-morning and late afternoon. If ticks quest mainly at night, or shift their activity into nocturnal windows during dry spells, then standard daytime dragging may systematically misestimate both true abundance and true biting risk. The authors point out that these commonly overlooked daily rhythms have important implications for estimating abundance in scientific research and surveillance programmes, and for interpreting how hazard varies across the day rather than across the year alone.

There are also ecological consequences for the transmission of pathogens among wildlife. Different host species are active at different times: birds, small mammals and deer partition the 24-hour cycle in ways that determine which hosts a nocturnal tick is most likely to encounter. If I. ricinus concentrates its host-seeking in the dark, the feeding opportunities available to it, and therefore the transmission circuits available to the pathogens it carries, may be structured by the clock as much as by the calendar. Reservoir hosts that forage at night could contribute disproportionately to infection cycles, while daytime-active animals, including humans, may benefit from the desiccation-driven suppression of tick activity during hot, dry daytime conditions. Understanding these synchronies could sharpen models of disease emergence and inform the timing of interventions, from acaricide application to public health messaging about when and where exposure risk peaks.

For the public, the practical message is nuanced rather than alarmist. Tick bites remain possible at any hour, and risk is shaped locally by habitat, vegetation and recent weather. But the study suggests that people walking in tick habitat during cool, humid evenings and overnight periods may face greater exposure than conventional advice implies, while hot, dry middays may offer comparatively lower risk, not because ticks are absent but because they are sheltering from the desiccating air. Dog walkers and other pet owners, whose animals often roam at dawn and dusk, should take particular note. As climate change alters temperature and humidity regimes across Europe, the seasonal windows and daily rhythms of tick activity are likely to shift in ways that current, daylight-biased surveillance is poorly equipped to detect. This year-round, round-the-clock field study offers a methodological template for closing that blind spot, and a timely reminder that the ecology of one of Europe’s most consequential disease vectors unfolds largely after dark.

Subject of Research: Seasonal and diel environmental drivers of host-seeking (questing) behaviour in the European tick vector Ixodes ricinus.

Article Title: Seasonal and diel environment effects on host-seeking behaviour in the European tick vector, Ixodes ricinus

Article References: Noll, M., Wall, R., Makepeace, B. L., & Rose Vineer, H. (2026). Seasonal and diel environment effects on host-seeking behaviour in the European tick vector, Ixodes ricinus. Parasites & Vectors. https://doi.org/10.1186/s13071-026-07679-5

Image Credits: AI Generated

DOI: 10.1186/s13071-026-07679-5

Keywords: Ixodes ricinus, ticks, questing behaviour, host-seeking, saturation deficit, diel activity, seasonal activity, vector-borne disease, Lyme borreliosis, tick surveillance, Parasites & Vectors, field study

The study, conducted by Ewelina Krawczyk of the Doctoral School of Exact and Natural Sciences at the University of Lodz and published in the journal Theoretical and Applied Climatology, examines the distribution of atmospheric water vapor and the patterns of moisture transport across Europe, with particular attention to how these processes shape humidity conditions over Poland. Using more than half a century of data from the ERA5 reanalysis produced by the European Centre for Medium-Range Weather Forecasts through the Copernicus Climate Change Service, the research covers the period from 1966 to 2020 at a spatial resolution of 0.25 degrees. The analysis spans a wide domain stretching from 30 degrees west to 45 degrees east and from 25 degrees north to 75 degrees north, capturing both the Atlantic Ocean, the principal moisture source for the continent, and the continental interiors of Western Asia.

Two key variables anchor the analysis. The first is total column water vapor, often called precipitable water, which measures the total amount of water vapor integrated through the entire depth of the atmosphere above a given point. The second is specific humidity, which describes the actual mass of water vapor per unit mass of air at particular altitudes. By tracking specific humidity at three pressure levels in the lower troposphere, at 925, 850 and 700 hectopascals, the study builds a vertical picture of how moisture is distributed from near the surface to several kilometers aloft. From these measurements, combined with zonal and meridional wind components, the author calculated horizontal specific humidity fluxes, a measure that captures both how moist the air is and how fast it is moving in a given direction.

The spatial findings are striking in their clarity. The Atlantic Ocean dominates as the source of atmospheric water vapor for Europe. Over the ocean at lower latitudes, total column water vapor can reach values of about 32 kilograms per square meter, considerably higher than anything observed over land. A second important source is the Mediterranean Sea basin, whose influence strengthens seasonally from May to October, when column water vapor there approaches 30 kilograms per square meter. Over continental Europe, moisture levels are lower and decline with altitude and latitude, dropping further in highlands and mountainous terrain. In Poland, inland conditions and cooler temperatures reduce column water vapor to roughly 8 to 10 kilograms per square meter in winter, while summer evapotranspiration and vapor transport from other regions lift it to between 24 and 26 kilograms per square meter. The subarctic remains the driest zone year-round, with persistently low vapor content.

Evaporation patterns help explain this geography. In the colder months, inland evaporation rarely exceeds 2 millimeters per day of water equivalent, while ocean surfaces evaporate at rates of roughly 3 to 6 millimeters per day, underscoring the Atlantic’s role as a vast standing reservoir of atmospheric water. By April, the contrast narrows, and in July something notable happens: evaporation over land, at 2 to 4 millimeters per day and sometimes higher, actually exceeds evaporation over the relatively cool Atlantic. The study found a moderate correlation between evaporation and column water vapor, ranging from a Pearson coefficient of 0.51 in April to 0.68 in July, indicating that local land-surface evaporation makes a substantial contribution to summer moisture, even as oceanic transport remains the decisive factor in winter.

Vertically, the picture changes rapidly with altitude. At the 925 hectopascal level, specific humidity over the Atlantic reaches up to 14 grams per kilogram in summer and 8 grams per kilogram in winter, while over Poland it ranges from just under 3 grams per kilogram in midwinter to 8 grams per kilogram in July and August. At 850 hectopascals, oceanic values fall to about 8 grams per kilogram in summer, and by 700 hectopascals, specific humidity over Europe generally stays below 4 grams per kilogram throughout the year. This vertical decline reflects both the temperature profile of the atmosphere and the intense exchange of water between the surface and the boundary layer, where most evaporation feeds vapor into the lowest layers of the air. Because the vapor reservoir thins with height, moisture transport weakens at higher altitudes even though wind speeds there are stronger and the westerly flow is more pronounced.

The transport analysis confirms what midlatitude meteorology would predict: the west is where Europe’s water comes from. The strongest specific humidity fluxes occur over the North Atlantic, reaching up to 60 grams per kilogram multiplied by meters per second in summer and locally 80 in lower latitudes at the 925 hectopascal level, propelled by both abundant vapor and vigorous winds. Over land, where surface friction slows the wind, fluxes mostly remain below 30. For Poland specifically, the study calculated fluxes arriving at the coordinates of Lodz in central Poland from each of eight compass directions. Western advection overwhelmingly dominates: the combined frequency of west, northwest and southwest arrivals never falls below 49 percent at 925 hectopascals in any month, rising above 65 percent at 850 hectopascals and above 72 percent at 700 hectopascals. The strongest fluxes from the west arrive in summer, with the July monthly mean reaching up to 61 in the relevant units at Lodz. Eastern advection is rare, slightly more probable in spring, and fluxes from the Arctic are weak, reinforcing earlier findings that the north supplies little moisture to the continent.

The long-term trends are where the study delivers its most consequential message. Between 1966 and 2020, trends in both total column water vapor and specific humidity across most of the domain are statistically insignificant. Where significant changes do appear, they are modest and regionally confined. The subpolar region shows a slight increase in vapor during the colder half of the year, typically up to 0.5 kilograms per square meter per decade for column water vapor. Central, Eastern and Northern Europe show increases during summer, generally not exceeding 0.4 kilograms per square meter per decade. The Mediterranean and Black Sea regions, by contrast, show seasonal decreases of up to 0.5 kilograms per square meter per decade from November to April. At higher pressure levels, trends shrink further, rarely exceeding 0.1 grams per kilogram per decade at 700 hectopascals. In short, the atmosphere’s actual moisture content has been remarkably stable.

That stability is precisely what makes the study’s conclusion about drying so important. According to the Clausius-Clapeyron relation, each 1 degree Celsius of warming increases the atmosphere’s water vapor storage capacity by roughly 7 percent. If actual moisture is not rising to match that expanding capacity, the saturation deficit, the difference between what the air holds and what it could hold, widens. The study argues that the documented increases in saturation deficit and the growing frequency of dry events over the region cannot be attributed to a decline in atmospheric water vapor, because vapor has not meaningfully declined. Instead, the evidence points squarely at rising temperature as the primary driver of atmospheric drying, a finding with significant implications for agriculture, forests and water resources, since plant transpiration and soil moisture loss respond to the vapor pressure deficit rather than to absolute humidity.

For Poland, the findings carry a double significance. The country sits at the crossroads of Atlantic and continental influences, and its moisture supply is tightly coupled to the western circulation that dominates the midlatitudes. Any change in humidity exchange over Western Europe could propagate downstream and alter moisture conditions in Poland. Meanwhile, the one region of the country showing a significant summer increase in precipitable water is the southeast, which the author links to stronger convective processes in its more continental climate. As warming continues, the steady Atlantic conveyor of moisture will remain essential, but the atmosphere above Europe will keep demanding more water than it receives, and that widening thirst, not any shortage of vapor in transit, is the story of European dryness.

Subject of Research: Atmospheric water vapor distribution, moisture transport over Europe, and their effects on humidity conditions over Poland

Article Title: Atmospheric water vapour distribution and moisture transport over Europe and their impact on the humidity conditions over Poland

Article References: Krawczyk, E. (2026). Atmospheric water vapour distribution and moisture transport over Europe and their impact on the humidity conditions over Poland. Theoretical and Applied Climatology, 157(10), Article 655. https://doi.org/10.1007/s00704-026-06593-1

Image Credits: AI Generated

DOI: 10.1007/s00704-026-06593-1

Keywords: water vapor, moisture transport, specific humidity, total column water vapor, Poland, Europe, Atlantic Ocean, evaporation, saturation deficit, ERA5 reanalysis, climate change, drought