Tick (S/F)

Ticks are ectoparasitic arachnids of the order Ixodida, and are closely related to mites. They are ecologically significant as parasites and can affect nearly every terrestrial vertebrate animal. All ticks are hematophagous, meaning they consume blood as food, and because of this diet they are vectors for at least twelve known blood-borne diseases.

These small animals are highly specialized as parasites; they have existed since at least the Cretaceous period, and are commonly found in amber. Some evidence suggests that they may have evolved as early as the Triassic period. At least one species, Deinocroton draculi, has been found alongside dinosaur feathers preserved in 99-million-year-old amber; this heavily implies that ticks fed upon dinosaur blood. Ticks can generally be classified into one of two families: Ixodidae, or hard ticks, and Argasidae, or soft ticks. A third family, Nuttalliellidae, contains only one species (the South African Nuttalliella namaqua) and is considered to be the most primitive of all the ticks.

Description

In order to avoid notice by the host, the majority of ticks are fairly small. They generally reach three to five millimeters in length, though a well-fed tick may appear bulbous and swollen to greater than its usual size.

Like mites, ticks have non-segmented abdomens; in addition, the abdomen of the tick is fused with the cephalothorax, giving the body a round or ovular outline when viewed from above. Unlike other arachnids, the body segments of the tick consist of the capitulum (the retractable mouthparts) and the idiosoma (the remainder of the body, including the brain and eyes).

The capitulum consists of only the mouthparts, which have three components. First is the basis capitulum, which is a support structure for the rest of the organ. Palps are also present, serving as sensory organs. Finally is the hypostome, a straw-like feature that is used to draw blood from the host. In the family Ixodidae, the capitulum projects forward from the body and is often described as being beak-shaped. This beaklike form helps to puncture the host’s skin.

Ixodid ticks can further be differentiated by their protective shell, or scutellum. This covers the whole back of the male, but in the female is considerably smaller. This allows the female’s body to become swollen with eggs. On the other hand, argasid ticks have more pear-shaped, leathery bodies and have their capitulum on the underside, where it is not visible when seen from above.

Ticks do have eyes, which are located on the sides of the body; however, they generally do not rely on eyesight to find hosts. Instead, they use their tactile sense to discern where to attach, and also use the Haller’s organ to detect smell, chemical signals, infrared radiation, and air pressure. Haller’s organs are located on the first leg pair; ticks, like other arachnids, have eight paired legs as adults. Each leg has seven segments and two claws at the end. They breathe through spiracles, which are located between the legs midway down the body.

Growth

All ticks go through four stages of life: egg, larva, nymph, and adult. To progress through each stage of life, the tick needs a blood meal. Larvae hatch with only six legs, gaining the final pair when they molt into nymphs. The growth stages differ somewhat between ixodid and argasid ticks; ixodid larvae start out by feeding on small mammals or birds, dropping to the ground once they are full and shedding their skin to become nymphs. The nymphs then feed on larger hosts, molting once more to become adults. The scutellum is reduced in size until the adult stage in the male; in the female it never grows as prominent. In the adult stage, females feed much more than males, who mostly remain on larger hosts to mate with females.

Argasid ticks have longer and slightly more complicated life cycles, molting several more times and going through as many as seven nymph stages. In these ticks, both the males and females feed on equal amounts of blood, and leave the host to mate.

Maturity in ticks may take months to years to complete. In particular, ixodids all take at least a year to fully mature.

Sexual Dimorphism

Depending on the family, ticks may or may not exhibit sexual dimorphism. In the family Ixodidae, sexual dimorphism is fairly prominent; males are completely covered by the shell-like scutellum, while in females, the scutellum is reduced to a small plate in the capitulum. In the family Argasidae, sexual dimorphism is much less noticeable, and merely consists of the location of the reproductive organs.

Habitat
Preferred Habitat

Ticks are found in most parts of the world, but are most common and successful in warm and humid regions such as Central America. They need moisture in order to metamorphose, and colder temperatures can harm their eggs. Species of ticks are distributed alongside their host species, but many inhabit areas of tall grass and woodland where they may more easily attach to hosts without being noticed. Migratory birds may carry them far outside of their original range.

Ixodid ticks have no dwelling place other than their host, while argasid ticks make their living in small spaces where they will return after feeding.

Isla Nublar

Costa Rica has numerous species of ticks, and those found on Isla Nublar are likely those that affect its indigenous animal life. Brown pelicans, for example, are affected by seabird ticks belonging to the genera Carios and Ornithodoros, which likely impact other seabirds that migrate to and from the island as well as birds that live there year-round. Meanwhile, nearly all boa constrictors found in northern South America bear the tick Amblyomma dissimile, and occasionally Amblyomma rotundatum. Mammals are also found on Isla Nublar, including native species including mantled howler monkeys, collared peccaries, and the endemic Nublar tufted deer as well as introduced species such as cattle, pigs, goats, and rats. Ticks that are found on these mammals include members of the genera DermacentorAmblyomma, Otobius, RhipicephalusHyalomma, Boophilus, Haemaphysalis, Ixodes, and others. All of these species may possibly have inhabited Isla Nublar. Because some of the animals found on the island are endemic, there is a good possibility that some tick species were endemic as well.

These hard-bodied Amblyomma dissimile ticks have embedded themselves between the scales of a Drymarchon snake. They could likely be found on islands in the Gulf of Fernandez, which are home to the common boa constrictor and other snake species. (Image taken by BugGuide user South Texas Guy, 2014)

Most of Isla Nublar was a superb habitat for ticks, which flourish in warm humid environments like the mist-shrouded tropical mountains and sun-drenched valleys of Isla Nublar. Dense undergrowth was present all over the island, which would have given native ticks many places to hide in wait of passing hosts.

The introduction of humans during ancient history would have introduced new mammalian tick species to the island, particularly those that infest humans and goats. In more recent history, the island was leased from the Costa Rican government by International Genetic Technologies, Inc., which brought cattle and invasive brown rats to the island; these probably further increased the number of ticks that would have lived there. Beginning in 1988, InGen introduced de-extinct life to the island. As most of Isla Nublar’s native vertebrate animals were birds and reptiles, many of the native tick species would have been able to infest dinosaurs without much difficulty. The larger size of the dinosaurs meant that they could potentially host larger numbers of ticks, which probably led to a surge in Isla Nublar’s tick population.

Isla Nublar was abandoned following a 1994 clean-up operation, allowing formerly developed areas to become reclaimed by nature and expanding the potential tick habitat. Furthermore, dinosaurs were no longer given veterinary care, which would have increased the likelihood of infestation. In 2002, Isla Nublar was reclaimed by InGen, now under the banner of Masrani Global Corporation; the island was much more extensively developed between then and 2005, which would have reduced the habitat ticks would thrive in. Over the next ten years, Jurassic World operated on the island. While the dinosaur and pterosaur population surged to well over two hundred fifty animals, the use of environmentally friendly anti-tick sprays by InGen staff ensured that infestation was a rarity. With many years of paleoveterinary knowledge at their disposal, Jurassic World’s staff members were much more prepared than Jurassic Park’s to cut back on disease and parasites in their animals. The tick population probably fell significantly between 2002 and 2015.

However, Jurassic World was abandoned after December 2015 due to an incident of corporate mismanagement which resulted in numerous human and animal deaths. Like in 1993, the island was left for nature to reclaim, and the tick population likely benefited. Despite the population of de-extinct animals dropping rapidly due to competition and resource scarcity, enough remained that the bird and reptile ticks in particular would have had no shortage of blood upon which to feed. On June 23, 2018, Mount Sibo erupted explosively, which destroyed much of Isla Nublar’s ecosystem; most of the terrestrial animals likely died out following this event, so only the seabird ticks and those that could feed on small, opportunistic survivors such as rats would have still had hosts.

Isla Sorna

Much like Isla Nublar, Isla Sorna is a lush, warm, humid tropical island with plenty of environment that ticks would flourish in. Unlike Isla Nublar, it was never extensively developed. This means that its tick population, which likely consisted of mostly species that are parasites on birds, reptiles, and amphibians, was probably not affected much by human activity. Beginning in 1986, InGen performed de-extinction on Isla Sorna; this would have introduced dinosaur and pterosaur species to the island which the bird and reptile ticks likely used as hosts. In Eric Kirby‘s account of Isla Sorna in the junior novels Survivor and Prey, ticks are among the small invertebrates mentioned as inhabiting the island. This would imply that some of the species found on Isla Sorna may use humans as hosts.

Isla Sorna is a larger island than Isla Nublar and has a more diverse range of habitats, from the redwood and pine forests of the northeast to the central tidal rivers and wet western jungles. Grasslands and mountains abound throughout, and fields of tall elephant grass would provide excellent habitat for ticks to hide in wait for passing hosts. This diverse group of arachnids would be able to thrive in most of Isla Sorna’s habitats, and with the introduction of such massive hosts as dinosaurs, their population would probably have boomed just as with Isla Nublar.

A soft-bodied tick of the genus Ornithodoros. This genus parasitizes birds and bats; species such as Ornithodoros knoxjonesi are known from Costa Rica. Photo taken by Alan R. Walker.

Movement of the dinosaurs by human intervention would have shifted the tick population around along with them. Between 2002 and 2004, dinosaurs were shipped back and forth between Isla Nublar and Isla Sorna, including most of the big herbivores which would have been major hosts. By late 2004, an ecological collapse on Isla Sorna (exacerbated by the aforementioned human intervention, as well as illegal activity) prompted InGen to relocate all of the remaining animals to Isla Nublar for their own well-being. This would have drastically cut down on the tick population on Isla Sorna, relocating huge numbers to Isla Nublar where they were likely exterminated by the park’s paleoveterinarians.

There is some debate over what has happened to Isla Sorna since, as the island is closely monitored and restricted to civilian personnel. If the island is truly abandoned as Masrani Global Corporation claims, it is most likely that the tick population has by now returned to pre-InGen levels.

Other

Ticks have a cosmopolitan distribution over the world, and are found wherever their host populations are dense enough and the humidity is great enough.

In particular, the game Jurassic World: Evolution portrays bird- and reptile-infesting ticks as existing on every island in the Gulf of Fernandez.

Behavior and Ecology
Daily Activity

Ticks, depending on the species, may be active at many times of day and night. They are not primarily visual, instead relying on chemical and tactile cues to move about. Their behavior is highly regulated by that of their hosts, but once they are attached, ixodids may remain in place feeding for days or weeks at a time while argasids usually feed for only a few minutes.

In general, ixodids engage in “questing” activity (seeking hosts) during the day while argasids bite their hosts during the night, but these are not strict guidelines for tick behavior.

Diet and Feeding Behavior

All tick species are obligate hematophage ectoparasites, meaning they cannot survive without a host from which they drink blood. While they can go long periods of time without feeding, they are unable to molt without a blood meal, so they must feed in order to mature. The preferred hosts and exact feeding strategies of ticks vary from one species to another, but follow a similar general pattern.

Ixodid ticks are long-term feeders. To find a host, most ixodids will position themselves in tall grass or dense foliage and reach two legs outward. When they feel something brush against their perch, they will grab onto it, crawling about on the surface of the skin in search of an ideal place to attach. The tick, once it finds a suitable spot, will use its mouthparts to pierce the skin and insert its hypostome to drink blood. In ixodid ticks, the bite is painless due to the small size and specialized anatomy of the tick, so the host may not even notice. These species will stay embedded in the host’s skin until they are full, which may take weeks. Ixodid ticks actually grow new cells to accommodate their expanding bodies during feeding; a full meal may see the tick increase its weight by as much as six hundred times.

On the other hand, argasid ticks will come out when their hosts are resting, often at night, and deliver a painful bite that lasts only a few minutes before the tick detaches and leaves for the safety of its home.

Social Behavior

Ticks are not naturally social animals, approaching one another only to mate. It is fairly common to find large numbers of ticks all in once place (unfortunate animals that stumble across such places may find themselves infested with dozens or even hundreds of ticks all at once), but this is not due to a social tendency. Instead, an ideal habitat may simply attract huge groups of ticks that are all seeking hosts at once.

Reproduction

Adult ixodid ticks will usually mate on their hosts; this is the main reason that the male, who does not feed as much as the female during adulthood, remains on the host. Because he keeps himself in this risky position in order to find mates, his exoskeleton has evolved to include a carapace-like scutellum which protects him. Sex roles are less gendered in argasid ticks, which exhibit very little sexual dimorphism and both feed on larger hosts as adults. Argasids leave their hosts to mate, because they do not usually remain attached for more than a few minutes when feeding.

An adult female tick may lay around three thousand small, spherical eggs in a single sitting. The incubation period differs between species, but no parental care is provided; the larvae are able to seek out hosts and feed shortly after hatching.

Vocalizations

Ticks do not make any noises to communicate, and beyond using chemical signalling to locate mates, they do not communicate with one another in any noticeable way.

Ecological Interactions

All ticks are parasites. Ixodids remain painlessly attached to their hosts for days or weeks at a time, while argasids scurry out while their hosts sleep to deliver a bite, drink for a few minutes, and retreat. In both cases, the interaction can be unpleasant for the host; argasid bites tend to be painful, and ixodids remain attached for long periods of time and can be a nuisance. More worryingly, many tick species can harbor blood-borne pathogens that they pick up from infected hosts. These can include bacteria, viruses, and other microorganisms that cause diseases such as Rocky Mountain spotted fever, Lyme disease, typhus, rickettsialpox, and others. One tick may contain multiple pathogenic microorganism species.

The hosts of ticks are also very diverse, and include all terrestrial vertebrate animals. Ticks are known from mammals, birds, reptiles, and amphibians. Coevolution between ticks and their hosts has resulted in a great diversity of tick feeding strategies, as well as defense mechanisms employed by the hosts. The relationship between ticks and hosts goes back at least 120 million years; the earliest currently-known ticks are believed to have been parasites on feathered animals, so birds and other theropod dinosaurs would have been common hosts. In the Genetic Age, de-extinct dinosaurs are affected by modern species of ticks, which have the deleterious effect of introducing diseases that the dinosaurs’ immune systems have no defenses against.

In rare cases, tick infestation can lead to a condition called tick paralysis. This is the only disease spread by ticks that is not a result of a blood-borne organism. There are at least forty-three species of ticks that can cause this condition, which is brought on by neurotoxins in the tick’s saliva. In North America, the best-studied species that cause tick paralysis are the American dog tick (Dermacentor variabilis) and the Rocky Mountain wood tick (Dermacentor andersoni), the latter of which is commonly found in the region of Western North America were numerous dinosaurs were released into the wild on June 24, 2018. Without paleoveterinarians to remove ticks, this condition could be fatal within days.

There are predators of ticks, however. Certain mites and nematode worms prey upon them, and small vertebrates such as birds may feed on ticks as well. Some birds will even pluck ticks from the bodies of larger animals, also feeding on blood that leaks from the fresh wound. Several species of birds found in the Gulf of Fernandez are frequently seen alongside herbivorous dinosaurs, sometimes even perching on them, and may potentially serve to remove ticks from these animals. Ticks of many genera are used as hosts themselves by the parasitoid wasp Ixodiphagus hookeri, which is found worldwide except for Antarctica. This wasp uses a symbiotic bacteria, Wolbachia pipientis, to weaken the immune system of the tick before laying its egg into the tick’s body; the egg hatches after a time and the larva feeds on the blood the tick has consumed before killing the tick as it emerges.

Interactions with Humans

Many of the species of mammal-infesting ticks can be parasites on humans, as with any other animal. These parasites can spread disease to humans by biting, introducing microorganisms that can then wreak havoc on the body.

However, humans are exceptionally capable of fighting tick infestations. Like many primates, their increased social behaviors allow them to inspect one another, and humans have access to specialized tools that can be used to remove ticks from the body. Medicine has been developed to combat the diseases that ticks may spread, though there are still many tick-borne diseases that cannot be cured and have lifelong impacts. Like with mosquitoes, solving the problem of tick-borne disease often comes down to removing the populations of ticks themselves.

In terms of de-extinction, ticks are significant as a source of diseases that de-extinct animals may not have defenses against. While ticks did exist in at least the Cretaceous period of the Mesozoic era (and could have been used by InGen to obtain paleo-DNA), the diseases borne by Cretaceous ticks are likely very different from those borne by ticks in the modern day. In Jurassic World, paleoveterinarians would be on site at all times to inspect dinosaurs for signs of infestation; anti-tick medications were used to deter the arachnids from attaching. In more recent times, anti-tick sprays have become ecologically friendly, ensuring that deterring ticks did not otherwise negatively impact Isla Nublar’s ecosystem. The Dinosaur Protection Group also prepared for the possibility of ticks infecting dinosaurs at any location that the animals might be safely transported, and promoted the use of the aforementioned anti-tick sprays as well as a more traditional manual inspection of each animal.

In Costa Rican Spanish, ticks are called garrapatas.