How ticks hibernate in the forest

Ixodid mites (Ixodidae), like all arthropods, are not able to maintain a constant temperature of their body. The main regulator for all processes of their vital activity, including the rate of growth and development, is the temperature factor.

The study of biotopes and pronounced natural locations in places where ticks overwinter, provided an idea of ​​the conditions of existence of parasites at low temperatures. It should be noted that the optimal hygrothermal factors for the existence of the parasite are in tropical latitudes. Due to the intensity of physiological processes in such conditions, the life of ticks here does not exceed one year.

On the territory of the Russian Federation and neighboring countries, the life cycle of the mite goes through several stages and lasts from 2 to 6 years, depending on the geographical latitude and climatic zone of habitat. Such a long term life implies the existence of a special evolutionary defense mechanism - a kind of hibernation, which allows not losing the ability to live during seasonal climate changes.

When adverse climatic conditions occur, the parasites pass into a special state - morphogenetic diapause, which helps them to safely endure wintering.

In the spring, after the end of the period of cold weather, Ixodides wake up and activate their vital processes. In mid-latitudes, the activation of adults and their intermediate phases occurs at a temperature of + 3 ... + 5 degrees Celsius.

It is important to know

Single adults, hungry larvae and nymphs are able to start the activation process after hibernation at temperatures from -1.5 ° C. The greatest activity of parasites in early spring is observed in the places of the first thaws and open elevations warmed by the sun's rays.

At all life stages, ticks are able to enter their bodies into a state of diapause at the onset of a certain average daily temperature level. A signal for hibernation is not only a decrease in the average temperature, but also the duration of daylight, as well as a change in the relative humidity of the air.

In central Russia, the peak of seasonal parasite activity ends in late October, and already in early November, most of the tick population goes into hibernation.

Hungry individuals of all phases of development, in contrast to those fed, are more resistant to low temperatures. The irreversible processes associated with metamorphosis and molt after feeding with blood, in most cases, reduce the cold resistance of the parasites.

Females who drank in the run-up to winter cannot control the activation of reproductive processes, and in any case will produce offspring, but the eggs do not have sufficient cold resistance, so most of them die already at near-zero temperature.

On a note

When staying for 30 days at a temperature of -2 degrees Celsius, the egg-laying of the female Ixodes tick dies by 99%.

Individuals that have fallen into a state of morphogenetic diapause are in a numbed state before the onset of a period of confident snowmelt and the transition of the average daily temperature to the positive zone.

The timing of the awakening and spring activation of the parasite is largely dependent on weather conditions and warming up of the soil.In late March-early April, the first parasite bites are recorded in central Russia.

 

Optimal conditions for wintering ixodic ticks

The main natural factors that motivate ticks to search for wintering grounds are the ambient temperature and day length. Photoperiodism inherent in many arthropods allows us to correctly estimate the time of occurrence of adverse temperatures and to find a place for wintering in a timely manner.

The choice of wintering grounds for ixodic ticks is largely due to physiological features and cold resistance. Despite the fact that the parasite is able to withstand short-term stay at temperatures up to -25 ° C, its optimal conditions for wintering are in the zone of near-zero temperatures.

With a long stay in the zone of low temperatures in the body of the parasite ice crystals form, which leads to its death.

It is interesting

The survival of ticks in the conditions of central Russia and more northern latitudes is possible only under the condition of a steady snow cover. With a snow cover thickness of 25-30 cm, the temperature at the surface of the soil does not fall below -6 degrees, even in thirty degrees of frost.If the thickness of the snow cover reaches 75 cm, then the temperature at the soil surface is on average -1 ° С.

Ticks always choose a place for wintering where the probability of snow blowing is minimized. These places are forest edges with low bushes, small forest glades with dense vegetation or windless dry lowlands with hilly relief, covered with young hardwood trees.

In preparation for hibernation, parasites select areas of the terrain where the species composition of trees and shrubs forms a thick forest floor. The loose layer of the forest bed moistened with autumn rains serves as a nutrient medium for aerobic bacteria and fungi. In the process of decomposition and decay, the remnants of vegetation emit some amount of thermal energy, thereby providing optimal conditions for wintering forest mites.

The most comfortable conditions for the wintering of all life phases of ixodid ticks are provided by forest litter, formed by young hardwood plantings, such as aspen, birch, mountain ash, alder, willow.Thick and friable bedding formed by such plants has excellent thermal insulation properties, retains moisture and is not an obstacle to oxygen access.

In coniferous age forests, forest litter is not so attractive for overwintering individuals due to its high density and low air permeability. In addition, fallen needles contain residues of volatile production and resins, the smell of which mites are trying to avoid. In the old-growth coniferous forests of the middle belt, a significant part of the snow lingers in the upper tier on closed crowns, therefore, an insufficiently thick snow layer forms on the soil. It can also cause the death of parasites in the winter.

When choosing wintering sites, mites avoid hard ground with bare rocks, as well as wetlands, sphagnum moss and dry areas with a predominance of sandy soils.

On a note

Many ticks overwinter in the holes of small rodents. In some cases, such parasites do not even fall into diapause, but continue an active lifestyle. And even after the onset of spring, they do not go anywhere and do not look for new owners for themselves, but continue to parasitize here on small vertebrates. A similar phenomenon occurs in the steppe regions with snowless winters.

 

Natural factors that have a negative impact on the survival rate of parasites in the cold season

Early November frosts, when the thickness of the snow cover is minimal or absent altogether, are the most common cause of forest mite population death.

On a note

Snow-free winters reduce the number of tick individuals in the natural focus by 60-70%. It takes 2-3 years to restore the population to the previous level (under favorable climatic conditions).

The areas of meadows covered with short grassy vegetation do not provide reliable insulation of the places where ticks overwinter, therefore, with the onset of cold weather, ixodides penetrate deep into the cracks of the soil and the holes of rodents.

Excessive soil moisture significantly impairs the insulating properties of tick habitats. Heavy autumn showers, replaced by frosts, often lead to hypothermia and death of the parasites.

But the greatest natural danger for the wintering of parasites is a thaw with full snowmelt and subsequent frost. Such phenomena cause a significant decrease in the thickness of the snow cover and the freezing of the soil to a great depth.

 

Peculiarities of wintering of ticks at different life stages

Life ixodic ticks due to cyclical. Each life phase has its own type of behavior, period of activity and method of hunting. Larvae, nymphs and adults have their own distinctive nutritional relationships. This biological feature allows for a more dense coverage of the habitat and more efficient use of food resources.

In the overwhelming majority of cases, all the vital phases of Ixodes ticks undergo a wintering stage. The exceptions are populations with a one-year development cycle in tropical and subtropical latitudes with warm winters.

Hungry females exhibit the greatest cold resistance. Long-term stay at a temperature of -2 ° С has practically no effect on their vital functions.

The most vulnerable phase of the parasite’s existence is the predated larva. Her death occurs in 3-5 days at a temperature of 7-10 degrees below zero.

Hungry larvae and fed nymphs are slightly more resistant to negative temperatures.

On a note

In the case of blowing snow cover by strong winds in the area where ticks overwinter,first of all there is a massive death of larvae and nymphs.

 

Winter activity of forest ticks in different climatic zones

The cold resistance of encephalitic ticks depends on the climatic zone of the permanent habitat of the population. In northern latitudes, parasites are most adapted to low temperatures.

On the territory of Russia, the most northern habitat of ticks is the coast of the Barents Sea. The tick populations that live in this harsh terrain, winter in bird markets, in the building substrate of sea birds, and penetrate deep into the cracks of rocks.

Severe habitat conditions often serve to prolong the life of ticks and increase the lifetime of each phase. Cases where parasites do not find food for themselves all summer and go to hibernate again are not rare.

Populations of ticks in Siberia are focal. Ixodide survival here depends on the stability of the snow cover and sufficient thermal insulation of the forest floor. In the taiga zone, parasites choose areas with mixed vegetation or fast-cut felling for wintering, avoid old-growing dry pine forests and open meadows.

In central Russia, the favorite wintering place for Ixodes ticks are areas with secondary forest plantations, meadows overgrown with aspen, and the edges of the forest with dense bushes.

In the south of our country, parasites hibernate for a relatively short period of time. In those regions where there is no steady snow cover, but frosts are possible, ticks make their way into the holes of small vertebrates or underground voids for the winter.

In the steppe and semi-desert zones, ticks are mainly found only in river valleys or areas with relatively dense vegetation. Overgrown with shrubs and reeds, the banks of the rivers are not only a convenient position for the waiting type of hunting, but also a good place for wintering.

 

What are the danger to humans and animals overwintering parasites

Although encephalitic mites are not active during the winter period and are in a state of diapause, they can still be dangerous for humans and domestic animals.

A tick bite in winter is not such a rarity, especially in rural areas, where residents harvest hay to feed their pets. In addition, parasites often get into the food of animals along with hay.

In rare cases, infection with tick-borne encephalitis is possible with the use of raw milk of goats or cows, into the digestive system of which the causative agents of this dangerous disease have got along with the carrier.

Ticks can enter household buildings along with fallen leaves, which are collected for litter pets. In warm barns where livestock lives, ticks can activate in the midst of winter and begin searching for victims. In this case, there is a threat of being bitten by both animals and the person caring for animals.

In all cases, the activation of ticks during wintering occurs only when it is physically moved to a warm room.

On a note

The probability that an encephalitic tick will be brought into the apartment from the forest with a Christmas tree is negligible. Ticks do not live and almost never hunt spruce, they use high grass and shrubs to trap the victim. Often ticks overwinter in cracks or hollows of large and thick trees, but young conifers do not provide reliable shelter for parasites in the winter.

Summing up, it is worth noting that, over millions of years of its evolution, Ixodic ticks have developed a very reliable survival mechanism at low temperatures.The ability of parasites to predict the onset of cold weather in advance and to find shelters effectively allows them to survive even in the most severe winters.

 

Interesting facts about the life of ticks

 

Testing the survivability of ticks under the action of various factors