How a tick bites: details about the process when it digs into the skin

All ixodid ticks are temporary obligate ectoparasites, and a specific feature of their life cycle is multi-day feeding, during which the tick is immobile at the place of its attachment on the host's body. At this time, the parasite uses the body of the host not only for food, but also as a true habitat.

At different stages of its development (larva, nymph, adult), the tick bites a suitable victim at least once - blood saturation is a necessary condition for the further development of the organism. At the same time, the tick is forced to periodically change from a free-living lifestyle to a parasitic one, and vice versa.

Despite these difficulties, ticks have many mechanisms of morphofunctional adaptations to such a lifestyle, which makes them one of the most progressive groups of hemoparasites.

 

Waiting for a victim with a tick and attacking her

One of the most important events in the life cycle of a tick is the finding of a host by a hungry parasite, on which it will feed.How quickly the tick finds a prey and how fully it feeds on it depends on its entire future life and partly on the development of the species as a whole.

Therefore, the entire feeding strategy is to use the host as a source of nutrition as efficiently as possible. To do this, the tick very carefully chooses the hunting grounds, the prey, and, moreover, the place of attachment to it (after all, choosing an unsuccessful place for a bite means with a high probability of being detected and killed).

On a note

It has been proven that behavioral responses aimed at searching for prey are activated only in hungry ticks that have reached the so-called "aggressive state". In this state, the functioning of the tick's sense organs and receptors is activated, and the parasite can effectively perceive the stimuli emanating from the future victim.

In ticks, 2 types of search and trapping of prey are observed:

• passive watchdog;
• active pursuit.

The passive way is to lie in wait for the victim in places of their frequent congestion (forest paths, pastures, parks and squares). Active pursuit is much less common, when the parasite, having sensed the prey, begins to actively move in its direction, approaching it. However, this mechanism is conditionally called an attack - the tick does not pounce on a person or animal, and contrary to popular belief, it does not jump or fall from trees.

On a note

Active pursuit is used by ticks extremely rarely, since it requires increased energy costs and, moreover, during forward movement on dissimilar surfaces, the parasite quickly loses moisture from the body.Therefore, after a short period of such a “hunt”, the tick is forced to stop chasing and descend into the moist upper layers of the soil or leaf litter, where absorption (absorption) of water through the integuments of the body is possible.

The victim search process consists of two phases. The first phase is the spatial orientation of the tick. At this moment, the arthropod qualitatively evaluates all environmental factors (humidity, temperature, chemical composition of the air) and climbs to the most convenient place for itself, often on grassy vegetation, after which it settles in its upper tier.

The second phase begins when the tick senses the approach of the prey. At the same time, he turns his body towards a possible owner, stretches the first pair of legs up and makes oscillatory movements. At the ends of his legs there are sharp claws, with which the tick clings to the clothes or wool (feathers) of the victim.

On a note

Ticks do not have a specialized organ that would help them determine the position of the body relative to the ground, so the animal is guided solely by the degree of tension of certain muscle groups of the limbs. When hunting, when the front legs are extended upwards, the remaining three pairs hold the body in the desired position, performing both attachment and sensory functions. Therefore, purely anatomically, the tick can neither bend down on the victim, nor fall on it from the tree.

If some time after the tick has smelled the host, contact has not taken place, but the stimuli continue to come out, the parasite descends to the ground and begins to crawl towards the victim.This is a purely instinctive process - the stimuli of the presence of the victim and hunger force the tick to resort to active actions, even if they are unprofitable from the point of view of physiology and energy costs. But if the parasite still digs in, this more than compensates for all the losses of energy and moisture at the hunting stage.

How do ticks sense prey? First of all, by the component composition of air. The strongest irritant is the increase in carbon dioxide. Other components released by the body of animals, including hydrogen sulfide and ammonia, also affect.

The main distant chemoreceptors are Haller's organs located on the forelimbs of ticks. They look like pits, at the bottom of which there is an accumulation of sensitive cells. These cells perceive the slightest change in the concentration of the above substances and induce the tick to act. A tick can sense a potential prey at a distance of more than 10 meters. This explains the massive accumulation of ticks in places where there are a large number of animals and people.

The question of whether ticks hear is still debatable. The vibration of the soil is, of course, an irritant, but does not induce the parasite to action.

In addition, being a cold-blooded animal, the tick clearly feels the infrared radiation of warm-blooded organisms, but for hunting it is still a secondary irritant.

 

How a tick clings and holds on to the host's body until it bites

When a person or animal passes through the grass where the tick sits, contact occurs, and the parasite mechanically clings to the hairline or clothes of the host with its paws. Further, his most important task will be to find a favorable place for suction.Up to this point, the parasite must cling tightly to the integument and not be noticed (one must protect oneself from the host's defensive actions, such as shaking).

The tick clings so tightly to the body that it is almost impossible to shake it off. The only way to get rid of a tick before it has stuck is to purposefully remove it from the surface of the body.

The high efficiency of retention on the host's body is achieved due to the special morpho-anatomical structure of the body of ticks:

• the entire body of the parasite is covered with small spines and bristles, which increase friction and increase the likelihood of engagement;
• there are sharp paired claws on the paws - they cling tightly to the tissue, like small hooks (for highly specialized ticks, the diameter of the bend of the claw can match the diameter of the victim's hair, and then a kind of lock is formed, which is extremely difficult to disengage);
• some of the ticks can bend the head section to their body, like pincers, pinching wool or tissue between the proboscis and the body;
• the body is flattened in the dorsal-abdominal direction, which complicates the task of crushing the parasite.

Until the tick has bitten, all these adaptations allow it to stay on the host's body for a long time, increasing the likelihood of successful feeding.

Given the size of the prey in relation to the size of the tick, the arthropod often has to travel considerable distances, so it may take several hours to select a bite site. Since the tick sucks blood for a very long time (usually for several days), the process of choosing an attachment site is extremely important and takes a significant amount of time.

On a note

From the foregoing, it becomes clear that the tick does not bite immediately. Between how he gets on a person, and how he bites, a significant period of time always passes. Therefore, if you examine yourself after walking in nature, you can avoid being bitten by a parasite.

 

Search for a place for suction and the initial stage of the introduction of the oral apparatus into the skin

Many species of ixodid ticks have specific attachment sites on the host body where the parasites are most common, while in other places bites are rarer or non-existent.

Such a rigid confinement to certain places on the body of the victim is due to a number of reasons. Firstly, this is the exceptional value of the ability of animals to self-cleanse: shaking, licking, gnawing, pecking and crushing parasites are used. Therefore, when attached to pets, ticks look for places where it is most difficult to clean themselves: ears, scruff, head, perianal and inguinal regions.

Another important factor is the microclimate in the chosen area of ​​the victim's body. Different areas of the skin have different temperatures and degrees of moisture, the nature of the secretions and the acid-base balance also differ. The ideal place for sucking the parasite should not be constantly exposed to direct sunlight, otherwise the tick will quickly lose its supply of water.

The actual structure of the skin is also significant - how coarse it is and how well vascularized it is.

On a note

In the case of wild animals, one should not lose sight of the aggregation factor, that is, when there are many ticks on one host at once. In this case, some types of parasites choose sites that are distant from the place of attachment of others.Parasites form local accumulations, which significantly reduces the effectiveness of local immune reactions of the host organism and increases the efficiency of feeding the ectoparasite.

The places of tick bites in humans have been well studied. Shoes and clothes limit the number of attachment points, but ticks find a way out of this situation.

The largest percentage of ticks attached to a person falls on the axillary region, then in descending order: on the chest, abdomen, groin, buttocks, legs. In children, there is also frequent attachment to the head. It is worth noting that ticks are perfectly oriented under clothing, making their way to the body even through small gaps.

 

The structure of the mouth apparatus of the parasite

The oral apparatus of the tick is a complex formation and consists of several components, each of which has its own morphology and functions. You can examine in detail some interesting nuances under a microscope (see photo below):

The oral apparatus consists of a base, a proboscis or hypostome, one pair of chelicerae immersed in cases, and a pair of palps. The base of the proboscis has the appearance of a capsule with a dense chitinous cover - here the ducts of the salivary glands pass and the pharynx begins. Palps have a segmented structure, consist of 4 segments and perform a tactile function.

The hypostome is an unpaired chitinous plate fixed to the base. It looks like an elongated “sting”, on which a large number of hooks bent back are located in regular longitudinal rows, as shown in the photographs below:

To the top, the hooks become smaller, forming a crown of small and at the same time very sharp spikes. When the tick bites, the sharp hypostome is involved in cutting through the skin along with the chelicerae.

The teeth of the proboscis directed backwards do not interfere with its penetration into the integument, however, they prevent the reverse violent removal of the attached tick, acting as an anchor. Therefore, in no case should a tick be forcibly pulled out of the skin with a sharp movement, as this threatens that the proboscis (or even the entire head of the parasite) may remain under the skin, causing suppuration.

On a note

At the base of the hypostome, a pair of chelicerae are attached, which look like sharp blades enclosed in cases. Chelicerae are very mobile and can cut through the skin and integument at different angles and to different depths. At rest, they are enclosed in cases that protect them from mechanical damage.

Together, this is called the gnathosoma and is the anterior part of the body of the tick, which during the bite is immersed in the integument of the victim's body.

 

How does a tick bite

After finding a suitable place to feed, the parasite begins to dig into the skin.

When the tick bites, it cuts through the upper stratum corneum of the skin, making alternate movements with sharp chelicerae. This is similar to how a surgeon wields a scalpel (only the parasite has two of them at once).

Despite the high mechanical strength of the upper layer of the skin, it does not create serious obstacles to the way of the tick's mouth organs to the inner layers, where the blood vessels are located. Moreover, there is no direct relationship between the thickness of the skin of the preferred host and the length of the chelicerae.

The process of cutting through the skin lasts the first 15-20 minutes from the moment the bite begins.

In parallel, the process of introducing the proboscis into the incision formed by chelicerae begins.The entire proboscis is completely immersed in the wound, almost to the base of the head, and the palps are bent almost parallel to the skin.

As a result, the length of the gnathosoma quite accurately reflects the depth of penetration of the tick into the integument - during the bite, the parasite penetrates deep enough, and the gnathosoma is located in the middle layer of the skin, rich in blood vessels.

On a note

Important is the fact that the tick is able to regulate the depth of penetration of the proboscis into the integument. It depends on the size of the victim and the thickness of their skin. It should also be taken into account that the deeper the tick sinks into the skin, the stronger the host's immune defense reaction will be. Severe inflammatory processes can begin that negatively affect the tick and reduce the chances of successful feeding.

Scientists have also noticed that species that have frequent host changes intrude at shallower depths, as this minimizes the chances of injury to the parasite's gnathosoma and increases the likelihood of success in the next feeding.

Thus, the entire stage of the actual bite (sucking) lasts quite a long time - usually it takes at least half an hour. All this time, anesthetic substances are injected into the wound, so the victim does not have an unpleasant sensation or pain. (along with saliva, anticoagulants and some other substances are also introduced). As a rule, it is possible to find out about a bite only when a parasite is found on the body.

Next, the process of feeding the tick occurs, a step-by-step description of which is given below.

 

The feeding process of the parasite

After the tick safely digs into the skin, it proceeds to feed. At this moment, along with the proboscis, there are also chelicerae with cases in the wound, which expand the tissues near the hypostome.

The proboscis is separated directly from the skin by a special cement case, which is a frozen secretion of the salivary glands of the parasite. Such a case has the shape of a tube and goes into the skin a little further than the top of the proboscis.

Accordingly, first the food enters the cavity of the case, and then into the pre-oral cavity of the tick. On the surface of the skin, this case ends in a frozen roller, to which the base of the proboscis is glued.

It is interesting

After a bite, the tick is retained in the host not only thanks to the hooks of the proboscis, but also due to outgrowths on the cases of chelicerae, which seem to be soldered into the walls of the cement case. This feature increases the reliability of attachment and protects the mouth organs of the tick from inflammatory infiltrate while the parasite is drinking blood.

It is worth noting that the tick feeds not only on blood, but also on lysed skin tissues, where the proboscis is inserted.

After the parasite has formed a cement case and is finally fixed, the process of blood sucking begins. There is an opinion that ticks prefer a certain blood type, but this is not so. The blood group has nothing to do with the choice of prey or saturation - ticks equally often bite people with different blood types.

At the stage of bloodsucking, anticoagulants are introduced into the host tissues, which prevent blood clotting, so that the parasite can feed for a long time. Additionally, digestive enzymes of saliva are injected into the wound, and partial dissolution of adjacent tissues occurs. Because of this, a local inflammatory process is formed in the host's body, which in some cases can spread and cause an increase in the temperature of the victim.

This is also dangerous because, together with the saliva of the tick, pathogens such as Lyme disease and tick-borne encephalitis can enter the host's body. Moreover, the longer the encephalitis or borreliosis tick eats, the more saliva it secretes and the greater the likelihood of a person being infected with the corresponding disease.

The duration of tick nutrition varies and depends on the stage of its ontogeny and sex. Nymphs drink blood for 2-3 days, and sexually mature females can stay on the host's body for up to a week. Males usually do not feed, and if the male individual sticks, then it stays on the host for only a few hours.

Long-term feeding of females is associated with a clear dependence of the success of egg development on the degree of saturation of the parasite. Only in a fully satiated female is it possible for the full maturation of eggs and their laying. Therefore, female ticks are the most active and dangerous to humans.

On a note

Distinguishing a female tick from a male is quite simple. The male has a wide chitinous matte shield on the upper side of the body, which completely covers the back, while in females the shield reaches only the middle of the back.

Tick ​​nymphs become saturated relatively quickly. They need food for molting and further development, but they are also carriers of pathogens of various diseases, like adults.

The body sizes of a well-fed and hungry tick differ significantly - they can increase 25 times! And even if it was not immediately possible to notice the bite of the tick, then after staying on the body for some time, the parasite is already difficult not to notice, since it becomes much larger (the engorged tick looks like a gray bag or grape).

The increase in the size of the body of the parasite during bloodsucking occurs unevenly.During the first day after attaching to the host, the size of the tick's body does not increase, but even slightly decreases, since significant evaporation of water occurs. The second stage is the longest, while the size of the tick increases by 10-20 times.

After the tick is completely saturated, it disappears by itself. The muscles of the oral apparatus relax, the chelicerae are tightly pressed against the proboscis, and the tick easily removes it from the integument of the victim's body.

After falling away from the host, the parasite becomes free-living again for some time - it looks for a favorable place in its natural biotopes (forest, park, square) and lays eggs, prepares for molting and wintering. It no longer contacts the former host - its function is completed, and the next stage of the life cycle of the parasite begins.

 

A few words about what to do if the tick has already stuck

As noted above, due to the substances contained in the saliva of the tick, a person or animal does not feel the bite of the parasite. Often people notice a tick on their body only when it has already sucked on and started feeding.

In any case, it cannot be pulled out of the skin by force and, moreover, try to crush it. Incorrect actions can lead to the fact that additional portions of infected saliva get into the wound, and the head of the parasite comes off the body and remains in the wound (this will cause suppuration in the future).

It is necessary to remove the attached parasite without undue delay, but as carefully as possible. You can do this yourself - there are several ways to properly remove a tick from a wound (see other articles on the site).If the bite occurred in a region potentially dangerous in terms of infection with tick-borne encephalitis or borreliosis, then the tick should be taken for analysis to the appropriate medical facility. If pathogens of a particular disease are detected in the parasite, further recommendations will be given by doctors - amateur activity here can already be dangerous.

We should not forget about preventive measures. After walking, you need to carefully examine yourself, children and animals, and before going out into nature, use repellents, wear closed clothes and shoes. With the right approach, it is almost always possible to remove a tick from clothes (or body) in time - long before it has time to stick.

 

Video recording of a tick bite at high magnification - all the details of the process are visible

 

Is it possible to pull a tick out of the skin with a syringe (vacuum): an experiment