"Winter" - what is it, definition of the term
The coldest season of the year, occurring when a hemisphere tilts away from the Sun, spans roughly three months—December to February in the Northern Hemisphere and June to August in the Southern Hemisphere. It is defined by the shortest daylight periods, consistently low ambient temperatures often below the freezing point, and widespread presence of snow, ice, or frost across many regions. This climatic phase results from reduced solar insolation due to Earth's axial inclination, leading to a distinct set of atmospheric and environmental conditions that differentiate it from the other three annual divisions.
Detailed information
The cold season imposes low temperatures, reduced daylight, and limited food sources, which directly influence the biology of ectoparasites such as ticks, insects, lice, and fleas.
During this period, many tick species enter a state of diapause, slowing metabolism and seeking insulated microhabitats beneath leaf litter, rodent burrows, or snow cover. Adult females often postpone oviposition until temperatures rise, while larvae and nymphs may remain dormant for several months.
Insects experience a contraction of activity. Species that feed on plant sap or decaying matter typically seek shelter in protected crevices or inside human structures. Some, like certain beetles, produce antifreeze proteins that prevent ice crystal formation within their cells, enabling survival at subzero temperatures.
Lice, being obligate human parasites, persist on hosts throughout the cold months. Their life cycle accelerates when hosts are confined indoors, leading to higher infestation rates in crowded or poorly ventilated environments. The lack of sunlight does not affect their development, as they rely on host blood rather than external conditions.
Fleas exhibit reduced mobility on the ground due to frozen substrates. Adult fleas often remain on mammalian hosts or in heated indoor spaces. Female fleas continue to lay eggs, but egg hatch rates decline as ambient temperature falls, resulting in a temporary decrease in population growth.
Key adaptations that enable survival across these groups include:
- Production of cryoprotectants (glycerol, antifreeze proteins) to lower freezing points.
- Behavioral selection of thermally stable microhabitats.
- Extended developmental pauses (diapause, quiescence) to synchronize emergence with favorable conditions.
- Reliance on host-provided warmth and nutrition, especially for obligate parasites.
Control measures effective during the cold season focus on environmental management: regular cleaning of bedding and carpets, sealing cracks that provide shelter, and maintaining indoor heating at levels that discourage parasite proliferation. Monitoring host animals for signs of infestation remains essential, as external conditions offer limited protection against ectoparasite transmission.