Dew

"Dew" - what is it, definition of the term

Dew is the thin layer of liquid water that appears on exposed surfaces when ambient air cools to its saturation temperature, causing water vapor to condense directly onto objects such as leaves, grass blades, or soil; this process occurs most often during nighttime or early morning under clear skies and low wind, creating a moist microenvironment that can sustain small arthropods, including ticks, insects, lice, and fleas, by providing necessary hydration and a favorable substrate for movement and survival.

Detailed information

Morning condensation forms when surface temperature falls below the saturation point of surrounding air, causing water vapor to change into liquid droplets. This process occurs most frequently on clear nights when radiative cooling exceeds heat input, and it requires relative humidity near 100 % at the ambient temperature.

Key environmental parameters that drive formation include:

• Air temperature drop of several degrees below the saturation threshold.
• Low wind speed, which limits turbulent mixing and preserves the cooling layer.
• Clear skies, allowing maximal infrared loss from the ground.
• High moisture content in the lower atmosphere.

For ectoparasites such as ticks, insects, lice and fleas, surface moisture creates a microhabitat that influences physiology and behavior. Specific effects are:

• Hydration: small droplets provide a readily available water source, extending survival during dry periods.
• Mobility: moist substrates reduce friction, facilitating locomotion across vegetation and host fur.
• Host‑seeking activity: elevated humidity triggers questing behavior in ticks, increasing the likelihood of attachment to passing hosts.
• Reproductive success: many species lay eggs in damp environments; morning condensation raises the humidity of leaf litter and soil, improving egg viability.
• Population regulation: prolonged wet conditions can promote fungal pathogens that infect arthropods, acting as a natural control factor.

Management practices that exploit these dynamics include:

1. Scheduling acaricide or insecticide applications during late afternoon, before condensation forms, to ensure contact with dry surfaces and reduce wash‑off.
2. Reducing canopy cover in high‑risk areas to lower nighttime cooling rates, thereby limiting moisture accumulation.
3. Maintaining low humidity in livestock shelters through ventilation, decreasing the favorable conditions for egg development.
4. Monitoring dew duration as an indicator of peak activity periods for questing ticks, allowing targeted inspection of animals and humans.

Understanding the relationship between surface moisture and arthropod biology enables precise timing of interventions and improves the effectiveness of control programs.