Difference between ticks and spiders

One of the most numerous and ancient groups of arthropods that arose during the time of dinosaurs and has survived to this day - mites, has more than 50 thousand species. Even acarologists, scientists who study this subclass, don’t know everything about ticks. Many species have been found and described, but due to the inaccessibility of arachnid habitats, little is known about their lifestyle and importance to ecosystems. Species that live near humans and often parasitize them have been studied in more detail.

Who or what is a tick

Small, six-legged and crawling. Who is this? Definitely some kind of insect. In fact, when answering the question whether a tick is an insect or an animal, you need to choose the second option. These peculiar creatures belong to the animal world and are arachnids. Unlike spiders, there are no poisonous mites. That is, they do not use the secretion of their salivary glands to kill the victim.

The Latin name for ticks is Acari. The name refers to the entire subclass. And the branch of zoology that studies these arthropods is called “acarology”.

Interesting!

Ticks are not insects, but traditionally many acarologists are members of the Russian Entomological Society.

People often classify any small multi-legged life form as insects, so this confusion will continue in the future. The Akari subclass is also similar to insects in stages of development that are usually absent in more developed forms of life. There are four such stages in arthropods:

• egg;
• larva;
• nymph;
• adult.

Depending on the type of tick, the nymph also has from 1 to 3 stages of development.

Who are spiders?

Spiders are a fairly large order of arthropods that have at their disposal animals that live in various parts of our planet. How many of these animals are there? In the latitudes of the former USSR alone, there are 2888 species. In some latitudes they are harmless, they have eight legs or four pairs of paws (as we understand), this is the same thing. Spiders are mostly engaged in creating webs. The implementation of this difficult task is required of them because they catch prey in such nets.

Then they run with their nimble legs to the insect caught in the net, and there they eat it. This is to briefly describe these habits. What do spiders look like? No wonder many people confuse them with insects. To some extent, they are very similar , since they belong to arthropods. But it is very easy to distinguish a spider from an insect. The latter has only six legs, while the spider has eight. This is the main difference. The body of spiders consists of a cephalothorax with an abdomen located at its other end.

Egg

Under a microscope, mite eggs resemble fish eggs. This is a large cell, covered with a soft membrane and containing the yolk, cytoplasm and nucleus. The outer shell can be smooth or ribbed. The eggs have different colors and two shells: the outer one is dense, and the inner yolk is thin. The shape of the egg can be:

• round;
• flattened;
• elongated;
• oval.

Each type of tick has its own specific egg shape.

The size of the egg relative to the body length of the mature female is very large. Typically the egg is larger than the last abdominal segment. After the eggs mature, the female lays them in a secluded, damp place.

Reproduction of ticks

Because of this, some species of ticks have developed a very original method of viviparity: postmortem. With this method, after the eggs ripen by autumn, the female does not lay eggs, but dies. The eggs remain overwintering in the female's body. In the spring, the larvae hatch and eat their way out into the wild. One of the reasons why ticks die is procreation. The uniqueness of this method of reproduction, according to experts, arose from the fact that the eggs are too large to be laid without the death of the female.

Interesting!

In two species: bread mites and pot-bellied mites, true viviparity is observed.

Building [edit | edit code ]

The sizes of arachnids vary from hundreds of microns (some mites) to several centimeters. The body length of araneomorphic spiders and harvestmen usually does not exceed 2-3 cm. The largest representatives of the class (scorpions, salpugs and flagellates) can reach 20 cm in length. Some tarantula spiders are even larger.

Traditionally, the body of arachnids is divided into two sections - the prosoma

(cephalothorax) and
opisthosoma
(abdomen) [2]. The prosoma consists of 6 segments bearing a pair of limbs: chelicerae, pedipalps and four pairs of walking legs [2]. In representatives of different orders, the structure, development and functions of the prosoma limbs differ [2]. In particular, pedipalps can be used as sensory appendages, serve to capture prey (scorpions), and act as copulatory organs (spiders) [2]. In a number of representatives, one of the pairs of walking legs is not used for movement and takes on the functions of the organs of touch [2].

Most arachnids do not have muscles in the distal parts of the limbs, so hemolymph pressure is used for movement (spiders, telephons) [3]. In scorpions and pseudoscorpions, the muscles are capable of bending two joints at the same time [4] [5].

The prosoma segments are tightly connected to each other; in some representatives, their dorsal walls (tergites) merge with each other to form a carapace [2]. In salpugs, the fused tergites of the segments form three shields: propeltidium, mesopeltidium and metapeltidium.

The opisthosoma initially consists of 13 segments, the first seven of which may bear modified limbs: lungs, crest-shaped organs, arachnoid warts or genital appendages [2]. In many arachnids, the prosomal segments fuse with each other, to the point of loss of external segmentation in most spiders and mites [2] .

Veils [edit | edit code ]

Arachnids have a relatively thin chitinous cuticle, under which lies the hypodermis and basement membrane. The cuticle protects the body from loss of moisture through evaporation, which is why arachnids inhabited the driest areas of the globe. The strength of the cuticle is given by proteins encrusting chitin.

Respiratory organs [edit | edit code ]

The respiratory organs are the trachea (in phalanges, false scorpions, harvestmen and some ticks) or the so-called pulmonary sacs (in scorpions and flagellates), sometimes both together (in spiders); lower arachnids do not have separate respiratory organs; these organs open outward on the underside of the abdomen, and less often on the cephalothorax, with one or several pairs of respiratory openings (stigmas).

The lung sacs are more primitive structures. It is believed that they occurred as a result of modification of the abdominal limbs in the process of mastering the terrestrial lifestyle by the ancestors of arachnids, while the limb was pushed into the abdomen. The pulmonary sac in modern arachnids is a depression in the body; its walls form numerous leaf-shaped plates with large lacunae filled with hemolymph. Through the thin walls of the plates, gas exchange occurs between the hemolymph and air entering the pulmonary sac through the openings of the spiracles located on the abdomen. Pulmonary respiration is present in scorpions (four pairs of pulmonary sacs), flagipes (one or two pairs) and low-order spiders (one pair).

In false scorpions, harvestmen, salpugs and some ticks, the trachea serves as the respiratory organs, and in most spiders (except the most primitive) there are both lungs (one is preserved - the anterior pair) and trachea. Tracheas are thin branching (in harvestmen) or non-branching (in false scorpions and ticks) tubes. They penetrate the inside of the animal’s body and open outward with the openings of the stigmata on the first segments of the abdomen (in most forms) or on the first segment of the chest (in salpugs). The trachea is better adapted to air gas exchange than the lungs.

Some small ticks do not have specialized respiratory organs; in them, gas exchange occurs, like in primitive invertebrates, through the entire surface of the body.

Circulatory system [edit | edit code ]

The circulatory system is not closed, it is represented by blood vessels that have their own walls, and a system of lacunae, or sinuses, cavities between organs. The pulsating dorsal vessel - the heart - is placed in the abdomen and has the shape of a tube, in the walls of which there are circular muscles and three pairs of slit-like openings - ostia, equipped with valves. The anterior aorta extends forward from the heart, branching into arteries, on the sides there are several pairs of arteries, back - the posterior aorta, from the arteries blood flows into the system of lacunae. Having washed all the organs, the blood then enters the peripulmonary sinus, is enriched with oxygen, returns to the pericardial sinus and through the ostia to the heart. [6]

Nervous system and sensory organs [edit | edit code ]

The nervous system of arachnids is characterized by a variety of structures. The general plan of its organization corresponds to the ventral nerve chain, but there are a number of features. There is no deuterocerebrum in the brain, which is associated with the reduction of acron appendages - antennules, which are innervated by this part of the brain in crustaceans, millipedes and insects. The anterior and posterior parts of the brain are preserved - the protocerebrum (innervates the eyes) and the tritocerebrum (innervates the chelicerae).

The ganglia of the ventral nerve cord are often concentrated, forming a more or less pronounced ganglion mass. In harvestmen and ticks, all the ganglia merge to form a ring around the esophagus, but in scorpions a pronounced ventral chain of ganglia is retained.

Sense organs

in arachnids they are developed differently. The sense of touch is of greatest importance to spiders. Numerous tactile hairs - trichobothria - are scattered in large numbers over the surface of the body, especially on the pedipalps and walking legs. Each hair is movably attached to the bottom of a special pit in the integument and connected to a group of sensitive cells that are located at its base. The hair perceives the slightest vibrations in the air or web, sensitively reacting to what is happening, while the spider is able to distinguish the nature of the irritating factor by the intensity of the vibrations.

The organs of the chemical sense are the lyre-shaped organs, which are 50-160 µm long slits in the integument, leading to a recess on the surface of the body where sensitive cells are located. Lyre-shaped organs are scattered throughout the body.

Organs of vision

arachnids are simple eyes, the number of which varies from 2 to 12 in different species. In spiders, they are located on the cephalothorax shield in the form of two arches, and in scorpions, one pair of eyes is located in front and several more pairs on the sides. Despite the significant number of eyes, arachnids have poor vision. At best, they are able to more or less clearly distinguish objects at a distance of no more than 30 cm, and most species - even less (for example, scorpions see only at a distance of several centimeters). For some vagrant species (for example, jumping spiders), vision is more important, since with its help the spider looks out for prey and distinguishes between individuals of the opposite sex.

Digestive and excretory systems [edit | edit code ]

The digestive system consists of the foregut, midgut and hindgut. The foregut is represented by the pharynx, which, tapering, penetrates through the central nervous mass and passes into the sucking stomach.

The pharynx is lined with a cuticle, the walls of the sucking stomach are formed by four cuticular plates, to which powerful radial muscles are attached. This organ serves to suck out the victim. Small glands located at the bases of the pedipalps and upper lip and usually called salivary glands open into the pharynx near the oral opening. The midgut in the cephalothorax has five pairs of glandular blind outgrowths, of which four pairs are curved on the ventral side and penetrate into the cavities of the coxae of the legs. The secretion of the perioral glands and blind processes has proteolytic properties (intensively dissolves proteins); it is introduced into the victim, turning its contents into a semi-liquid pulp, which is absorbed, i.e. the spider experiences partial extraintestinal digestion.

In the abdomen, the midgut is arched, and several pairs of branching blind glandular appendages open into it, which fill the upper half of the abdominal cavity in a dense mass. This is the so-called liver, which secretes digestive enzymes and serves to absorb nutrients. In the liver, food is partially digested intracellularly. The midgut passes into a small hindgut, which forms an extension - the rectal bladder. At the border of the middle and hind intestines, tubular excretory organs open - the Malpighian vessels. Remains of food and the secretion of the Malpighian vessels accumulate in the rectal bladder and are excreted through the rectum, which opens on the anal tubercle. The midgut and Malpighian vessels are formed in embryonic development from the endodermal rudiment, the foregut and hindgut - from the ectoderm. [6]

Genital organs [ edit | edit code ]

All arachnids are dioecious and in most cases demonstrate pronounced sexual dimorphism. The genital openings are located on the second abdominal segment (VIII body segment). The majority lay eggs, but some orders are viviparous [7] (scorpions, bichorchis, flagipes).

Some representatives of the class are characterized by parthenogenesis.

Nymph

Not all types of ticks go through all three stages in their development. Three instars are present in ixodid and argasid ticks. Sarcoptoid and teranichidae pass through the 1st and 3rd instars. Thrombidiform mites pass through the first two instars. Each age has its own name:

• protonymph;
• deutonymph;
• Tritonymph.

The protonymph already has 4 pairs of legs, which still have very few setae. Also at this stage, a genital opening and 2 genital setae with a pair of genital tentacles appear.

In deutonymphs, the number of setae on the tarsi increases. 6 genital setae and 4 genital tentacles appear.

Tritonymph continues to acquire genital tentacles (already 3 pairs) and setae. The number of tactile bristles on the legs and body surface increases. If you look at the images of all three forms, you can see that the anatomy of the third instar nymph is almost no different from the morphology of ticks.

What structural features of ticks and spiders indicate their similarity?

Although ticks and spiders have some similarities, it is quite easy to distinguish them from each other. For example, they have similar characteristics, belong to the same class - arachnids, and arachnology studies them in detail. This pair of close “relatives” has many similarities.

The main similarities between ticks and spiders are four pairs of legs and simple eyes.

These photos show a spider that looks like a tick:

Sexually mature individual

Ticks
The structure of a tick is usually considered using the example of ixodid ticks as the most common in the world. This group is the most dangerous.

External structure

The tick usually has an oblong body, where the thorax and abdomen are fused together. Hungry individuals are flat above and below. Well-fed females resemble a leathery pouch. The tick's "skin" is actually a chitinous cuticle. On the back of arthropods, a compacted cuticle forms a protective shield. In females this shield is located only on the front part of the body; in males it covers the entire dorsal part. Under the cuticle are the internal organs and muscles of bloodsuckers.

Interesting!

Some species of ixodids also have scutes on the underside of the body.

In the photo of the tick under a microscope you can see the lateral appendages of the arachnid. In many species, the length of the appendages is so different that it is often impossible to understand how many legs a tick has. But all species of these animals have only 4 pairs of legs. What may appear to be the front legs are actually the chelicerae and pedipalps of the tick, which are part of the structure of the mouth apparatus.

On a note!

Chelicerae and palps in ticks also belong to the limbs. These limbs may once have been another pair of legs, but today they are included in the mechanism of the oral apparatus.

Head

The head is so small that the proboscis seems attached directly to the body. The piercing-sucking mouthparts of the tick have changed significantly compared to the gnawing apparatus. The tick's proboscis has a hexagonal or rectangular base. The structure of the proboscis is quite complex:

• chelicerae;
• pedipalps;
• hypostome.

The latter in ixodids is equipped with teeth that help to stay on the victim. Chelicerae in some species of arthropods have turned into a kind of scissors. The sucking ones have fused into a hollow stylophoran tube. Stylophore – protection for stylets formed by modified cheliceral fingers. In bloodsuckers, these “fingers” are transformed into a tube through which blood enters the digestive tract.

On a note!

The pedipalps (palps) have only an auxiliary value and are often reduced.

Legs

The adult has 4 pairs, the larva has three. The legs of the mite are homologous to the limbs of insects:

• pelvis;
• swivel;
• hip;
• knee;
• shin;
• paw.

Since the tick clings to the victim first with its front pair of legs, the legs of predatory and parasitic species are equipped with hooks and suction cups that help to stay on the animal.

Appearance of a tick

In most species of ticks, the pelvic part is motionless and fused with the body. Only primitive species retained mobility of the pelvis. Given the microscopic size of the objects of study, it is possible to examine the segments on the legs only through a microscope under high magnification. A close-up illustration of the arachnid’s legs shows that the segments are very similar and it is very difficult to distinguish them from each other.

Throughout its life, a tick's limbs may change. The main anatomical change occurs in the hind limbs. In predatory species they are curved and look like pincers, with the help of which the arthropod is held on the victim. Leading a “calm” parasitic lifestyle of scabies, the legs are thickened, shortened and have powerful suckers. Tetranych mites have glands on their legs that secrete a sticky liquid that helps them move along smooth surfaces.

Internal systems

The diagram shows an dissected female ixodid tick that has drunk blood, indicating the purpose of the internal organs depicted.

The internal life support systems include digestive and respiratory. The circulatory system of ticks is not developed. The analogue of the heart muscle is located on the back and has an oval shape. The aorta comes off from it. The vascular system is not developed, and the blood - a white liquid in the tick - pours into the body cavity.

The digestive system is represented by:

• mouth opening;
• two salivary glands;
• pharynx;
• esophagus;
• intestines;
• anus.

The excretory organs of mites include not only the latter, but also several more. The intestines have a more complex structure:

• midgut with several lateral blind branches;
• small intestine;
• hindgut.

Adjacent to the hindgut is the rectal bladder, which is one of the excretory organs.

The excretory organs, in addition to the rectal bladder, include the salivary glands located in the mouth. Salivary glands are needed by parasites to store an anesthetic secretion, which is used for injection when piercing the skin with the proboscis.

Important!

Thanks to the secretion of the salivary glands, the bite of an arthropod is invisible to the victim.

The rectal bladder is a repository for waste products, as it receives digestion products and dead cells of the midgut. Pathogens found in the intestines also come here. For this reason, tick feces can also be hazardous to health.

Respiratory system

Tick ​​bite
When a tick bites into the skin, it breathes not through the anus, but through the respiratory openings - stigmata on the hind legs. When inhaled, air enters the trachea - thin tubes running along the entire body of the arthropod. The stigmata of ticks are protected by special organs called peritremes. In ixodids, peritremes are plates that are adjacent to the stigmas from the sides and behind. Other groups have tubes of varying degrees of length and shape.

The respiratory system of this subclass of arthropods is very poorly studied. The question of what a tick breathes actually remains open. If we talk about the respiratory organs, then these are the trachea. If we consider the composition of gases, the needs of arthropods have not yet been studied. There is a group of granary mites that can live at a CO₂ concentration of 30%.

Arachnids - similarities and differences

The class of arachnids includes spiders, mites and scorpions. All these creatures have a similar structure and are mainly land dwellers. How are ticks different from spiders? There are quite a lot of differences between representatives of this class. First of all, this is the structure of the body. Spiders have two distinct sections – the cephalothorax and abdomen. Ticks do not have such a boundary; their body is solid. All spiders are predators; among mites there are many species that feed on organic debris or living plants.

The fluctuation in size is similar. Both groups have representatives invisible to the naked eye with a body length of 0.3 mm. They have the same number of limbs - 4 pairs of walking legs. They have spikes and suction cups to hold them on the host's body. Both species are armed with claw-like processes - chelicerae. Most arachnids are covered with a chitinous shell. Their respiratory organ is the trachea; only small species breathe with their whole body.

And a few more facts:

• The smallest tick measuring 0.08 mm is listed in the Guinness Book of Records.
• In the absence of food, the argas species engages in omovampirism - it sucks blood from an engorged individual.
• The number of ixodid ticks is controlled using hedgehogs. Animals cannot get rid of the parasite on their own. Observers count how many parasites cling to a hedgehog per hour.

A Little-Known Tick Threat

The information that ticks are carriers of dangerous infectious diseases is known to everyone today. But there is also medical significance in the fact that this group of arthropods can be carriers of other parasites.

The question of which parasite has a tick as its intermediate host is of little concern to the average person. And this is correct, since the parasites are quite exotic. These are worms.

There are two types of worms that can cause inermicapsiferosis and berthiellosis in humans. The final hosts of worms are rodents and rabbits in the first case and monkeys in the second. A person becomes infected with these worms by accidentally ingesting a tick. Disease prevention has not been studied in medicine.

How many legs do a spider and a tick have and how to distinguish these animals

A rather interesting question is how many legs a spider has. A very large number of people confuse these animals with other arthropods, in particular insects or mites. Therefore, this article will answer not only the question of how many legs a spider has, but will also make a comparison with ticks, since the latter also belong to arachnids.

It is especially important to consider that the ability to distinguish our hero from a tick is also important in practice.
In particular, the latter are carriers of a large number of diseases or simply provoke allergic reactions in the body.

Myths about ticks

Ticks
There are many myths about ticks. Some of them are relatively harmless, others are potentially life-threatening. It wouldn’t hurt to debunk many myths in life safety lessons for schoolchildren.

• In hot weather, ticks dormant. Misconception. Activity decreases in hot weather, but only in cold regions. In hot weather, ixodid ticks have perfectly adapted to high temperatures and it is not even clear whether they sleep at night. Even in winter, ticks are unlikely to sleep in the usual sense of the word. They fall into a stupor, from which they emerge as soon as the air temperature rises.
• Ticks hunt by jumping from trees. No. Usually ticks wait for their prey on plants no higher than 1.5 m: grass and bushes. They rarely rise above 1 m, and never above 1.5 m. Only the Persian tick, which belongs to the Argasaceae, can fall from the ceiling.
• Ticks live only in forests. In fact, they live even where all the forests were destroyed 2000 BC. And these are “traditionally forest” dogs. Many representatives of ixodids feel great in the steppes and meadows.
• If a tick is thrown into water, it dies. You can check whether ticks drown in water experimentally. They don't drown.
• If the tick has burrowed recently, there is no danger of contracting an infectious disease. The causative agent of encephalitis enters the bloodstream when the tick injects its fluid into the wound.
• If there is no increasing inflammation at the site where the tick was attached, then there is no infection with borreliosis. Wrong. If there is inflammation at the site of the bite, this is a guarantee of infection. If there is no inflammation, then you need to get tested, since inflammation does not always occur with borreliosis. Checking cannot be neglected. Although without treatment, Lyme disease does not end in death, but it does cause severe complications in all body systems.

How to protect yourself from parasites

Vaccination against encephalitis and the use of repellents are suggested as preventive measures. When visiting the forest, it is advisable to choose the right clothes. It should hide the arms and legs; it is advisable to have a headdress. The period of parasite activity is late spring and early summer. The second wave begins with a decrease in temperature in August-September. At this time, you should be attentive to yourself and your pets.

Advice. Choose light-colored clothing for hiking; brown ticks are easier to spot on them.

How dangerous are ticks?

In addition to blood-sucking species that spread deadly diseases, there are many ticks that cause trouble. They are a source of irritation and allergies in people and pets. Some are unlikely to cause damage to gardens, fields, and settle on indoor plants. Among the species that exist near humans:

• Gamasidae - parasitize birds and rodents, causing significant damage to poultry farms. Causes feather loss in chickens.
• Scabies is a microscopic parasite that causes an intractable skin disease.
• Ear - settle in the ears of domestic animals - cats and dogs. Cause severe inflammation, itching and scratching. Treatment with acaricidal drugs is required.
• Subcutaneous or demodecos - present in limited quantities on the skin of most people. With pathological spread, they cause itching and redness. Size 0.2 mm.
• Dust or bed - the microscopic inhabitant of house dust provokes allergies with its excrement.
• Arachnoid is a phytophage in the arachnid family, feeding on plant sap. It is a carrier of disease and rot.
• Flour - damages the reserves of granaries, contaminates flour with its waste. Promotes the spread of mold.

Where do mites come from in apartments? They get into homes with dust, on people's clothes, and animal fur. Favorable indoor conditions and an abundance of food lead to their spread.