TICKS
Three
things distinguish ticks from insects:
(1) The head,
thorax, and abdomen are fused into one body segment;
(2) They do not have antennae; and
(3) In the nymph and adult stages they have four pairs of legs.
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Hard
ticks found in Texas:
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General Characteristics and Habits of HARD TICKS
(Family Ixodidae)
Hard ticks have a scutum while soft ticks do not. In the male hard
tick, the scutum is large, completely covering the dorsal surface. In the
female, the scutum covers only a part of the dorsal surface and is almost
obscured when she becomes engorged. The capitulum of hard ticks extends forward
from the anterior end of the body, bearing some resemblance to a true head,
while in soft ticks it is found on the under side and is not usually visible
from a dorsal view. The spiracles lie behind the fourth pair of coxae, or basal
segments of the leg.
Hard ticks typically take one blood meal in each of the three developmental stages -- larval, nymphal and adult. Both sexes are blood feeders, but only the female becomes greatly distended during engorgement. Most species feed on a different host during each stage, but there are some one-host and two-host species.
Genus
Amblyomma
Most species of
Amblyomma have whitish markings, long palpi, a long hypostome, and
festoons on the posterior margin of the abdomen. Only eight of the more than 90
described species are found in the United States, Amblyomma being more
common in the tropics. It is found east of central Texas to the Atlantic Coast
and northward to Iowa.
The lone star tick, Amblyomma americanum, can carry spotted fever, tularemia, and possibly Q fever. Female specimens are easily recognized by the conspicuous silvery-white spot at the tip of the scutum, hence the name "speck-back" in the Ozark Mountains and the common name "lone star tick" for the Lone Star State of Texas. The pale markings are diffuse on the male specimens. In the southern states east of Texas this species will bite man readily in the larval, nymphal and adult stages. Its bite is quite painful and may itch for a long time. Common hosts are livestock, dogs, deer, birds and man.
The Gulf Coast tick, Amblyomma maculatum, is found particularly along the Gulf and South Atlantic coastlines. It has spurs on the second, third and fourth pairs of legs and more diffuse pale markings on the female than does the lone star tick. When present in an area, the ticks often infest the ears of cattle. Screwworm flies are often attracted by the smell of fresh blood in these wounds, laying eggs in them. Later screwworm larvae may feed voraciously, cause festering sores that can kill cattle. Common hosts include livestock, deer, dogs and man.
Genus
Dermacentor
The genus
Dermacentor is the most important group of ticks in the United States as
pests of man and other animals, both as blood-sucking parasites and as disease
vectors. Some species feed regularly on man and other animals; transmit the
causative organisms of spotted fever, tularemia, Colorado tick fever, possibly Q
fever, and anaplasmosis; and pass many of the causative agents of these diseases
transovarially and transstadially. Specimens of D. variabilis and
D. andersoni are the ticks most frequently involved in cases of tick
paralysis in the United States. Dermacentor ticks are ornate, with pale
markings on the scutum, eleven festoons, eyes, and short palpi. The basis
capituli is quadrangular dorsally.
The American dog tick, Dermacentor variabilis, is widely distributed east of the Rocky Mountains and also occurs on the Pacific Coast, and in parts of northern Idaho and eastern Washington. This tick will be discussed in detail as a representative of the hard ticks.
The dog is the preferred host of the adult D. variabilis, although it feeds readily on mainly large mammals including man. The adult ticks are commonly found in the spring in their "waiting position" on grass and other low vegetation. The third pair of legs is used to cling to the grass while the others are waved about ready to grasp any host that comes by. The male remains on the host for an indefinite time, alternately feeding and mating. The female feeds, mates, becomes engorged, and drops off to lay several thousand eggs.
The adult male and females are frequently encountered by sportsmen and people who work outdoors. The males and females have pale whitish or yellowish markings on the scutum. Males may be only 3 mm long, while engorged females may be as much as 13 mm in length.
Larvae seek the host actively and do not assume the waiting position typical of the adults. Meadow mice, white-footed mice, and pine mice are important hosts of larvae.
Males of D. variabilis do not feed enough to alter their size noticeably. Females may increase in size from about 5 mm long and 2.5 mm wide to 13 mm long and 10 mm wide, but their engorgement is retarded if males are not present. The newly hatched larvae are about 0.6 mm long, without spiracular plates, and are yellow with red markings near the eyes. Engorged larvae are about 1.5 mm long and are slate gray to black. Nymphs are similar in appearance to the larvae, but have four pairs of legs and are light yellowish brown with red markings near the eyes. Engorged specimens are slate gray and about 4 mm in length. The entire life cycle is from four months to more than a year.
American dog ticks, as well as other species, are attracted by the scent of animals, hence are most numerous along roads, paths and trails. Engorged ticks that drop from animals using the passageways further increase the concentration at these sites. These facts are important to persons applying pesticides for tick control.
The Rocky Mountain wood tick, Dermacentor andersoni, is found in the Rocky Mountain states and in southwestern Canada. The life cycle of this three-host tick is two to three years. The larvae and nymphs attack small mammals, and the adults obtain their blood meals from large mammals including man. The range of this tick coincides with the area in which cases of Colorado tick fever are contracted. It is similar to the American dog tick, but adults of the wood tick in general have more pale coloring and larger goblets on the spiracular plates than the American dog tick.
The winter tick, Dermacentor albipictus, is widely distributed throughout North America. It is a one-host species parasitic on cattle, horses, moose, elk, deer and sometimes man. These ticks may be extremely numerous on these large animals and may cause blood loss leading to anemia and even death. The spiracular plates are oval with very large goblets.
The Pacific Coast tick, Dermacentor occidentalis, is a three-host tick whose life cycle on small rodents and large mammals may be completed in less than three months. It is a serious year-round pest of cattle and will attack man. It is a known vector of tularemia and a suspected vector of Rocky Mountain spotted fever. The basis capituli has conspicuous tooth-like dorsal projections on the posterior margin known as cornua.
Genus Ixodes
Ticks in the genus Ixodes are easily recognized by the
position of the anal groove, which lies in front of the anus and extends from
one side of the body to the other. There are 34 species of ticks in the genus
Ixodes in the United States, more than in any other genus. Male specimens have a
complicated arrangement of plates on the ventral side of the abdomen. Most
species have enlarged club-like palps.
The black-legged tick, Ixodes scapularis, occurs in the eastern half of the United States. Male and female specimens are frequently found mating on deer, dogs and other large mammals in the fall and winter. This species will also feed on man and birds.
The Pacific tick, Ixodes pacificus, is the western counterpart of I. scapularis, and both species are related to the castor-bean tick of the Old World, Ixodes pacificus. Ixodes pacificus adults will bite deer, cattle and man readily.
Genus Rhipicephalus
Many species of ticks in the genus Rhipicephalus occur in
Africa and Asia where they are important vectors of disease to man and animals.
These ticks have a hexagonal basis capituli, eyes on the scutum and festoons on
the posterior margin of the abdomen. Male specimens are distinguished from most
other common ticks by the adanal plates and accessory plates on either side of
the anus.
The brown dog tick, Rhipicephalus sanguineus, is found in most of the United States. It is a reddish-brown species that attacks dogs and other mammals but rarely man. It is not known to transmit human diseases in the United States, although it is a known vector of Marseilles fever in the Mediterranean region. The ticks are frequently found attached to the ears and in between the toes of dogs. This species is one of the most common in homes, where it feeds on dogs and then drops off the infested animal. The engorged female specimens, sometimes about a 13 mm long, are particularly noticeable as they crawl on walls or around baseboards and cracks, looking for protected areas in which to deposit 1,000 to 3,000 eggs.
The life cycle of this species can be completed in less than two months. In the southern United States this species occurs in buildings, kennels and small animal hospitals, and outdoors in yards. In the North, this tick is rarely found outdoors. It is a very difficult and important species to control.
General
Characteristics and Habits SOFT TICKS (Family Argasidae)
Male and female soft
ticksare similar in appearance, with no dorsal plate (scutum) to distinguish the
sexes as in hard ticks. The capitulum which bears the mouth parts is located
beneath the anterior margin of the body. The spiracles or respiratory openings
lie on the sides of the body above the third and fourth pairs of legs. Although
some species of soft ticks feed on humans, they are more common on birds and
occasionally are found on bats and other small mammals. The sexes can be
distinguished by the shape of the genital opening which in males is circular or
crescent-shaped and in females is a transverse split, wider than long.
Genus
Ornithodoros
Ornithodoros
is the most important of the four genera of soft ticks. The ticks in this genus
have a more globular body without the sutural line found in the various species
of Argas. The body is roughened or warty in appearance with tiny protuberances,
called "mammillae." The hypostome has well-developed teeth. Several species are
known in the United States, including Alaska and Hawaii, of which four are known
vectors of relapsing fever in the United States.
The relapsing fever ticks, Ornithodoros species, are seldom seen by the average person since they are primarily "nest ticks" which can survive starvation for months or even years. Human beings are occasionally bitten by these hungry ticks and contract cases of relapsing fever in mountain cabins, in caves, or near wild animal burrows. For example, O. hermsi is found at high elevations in the West, particularly Idaho, Oregon, Washington, California, Nevada, and Colorado, where it parasitizes small mammals such as the western chipmunk (Eutamias) or tree squirrels (Tamiasciurus). Occasionally, people sleeping in mountain cabins come in contact with infected ticks and contract relapsing fever. Ornithodoros parkeri is a large species which attacks man and rodents and is found in nine western states. It is an efficient vector of relapsing fever and can transmit Rocky Mountain spotted fever. Ornithodoros Turicata, also a large tick, is found in the southern and western United States. It is found in caves, holes made by burrowing animals and at campsites. Its hosts include rodents, snakes, terrapins and various domestic animals, as well as man. Even after long starvation, it is an efficient vector of relapsing fever. Both O. Turicata and O. parkeri transmit the spirochete of this disease to their offspring as far as the fourth generation. Ornithodoros talaje occurs in southern United States.