What are Ixodes and where are they found?
Ticks are arachnids (related to spiders and mites) that live in low
brush and grasses. Ticks feed on blood, and their principal prey is a
rodent called Peromyscus leucopus,
the white footed field mouse. However, ticks are opportunistic feeders
and will take a blood meal from whatever unfortunate animals that comes
by their perch. There are over 850 different types of ticks worldwide,
which are categorized into two broad groups based on their structure and
outer skin. Hard bodied ticks are in the Ixodes family and soft bodied ticks are in the Argasidae family. In North America, Lyme Disease is transmitted by two species of Ixodes. These are Ixodes scapularis (geographic locations are in red and blue), found in the eastern half of the continent and Ixodes pacificus (geographic locations are in green and yellow), and found along the Pacific coast.
Counties
classified as established (red or green) for a given tick species had
at least six ticks or two life stages recorded within a single calendar
year. Counties with fewer ticks of a single life stage were classified
as reported (blue or yellow) for the tick species. Counties shown in
white indicate “no records.” J Med. Entomol. 53(2):382
In Minnesota you are likely to come across three different hard bodied ticks: Blacklegged tick (Ixodes scapularis), Common dog tick (Dermacentor variabilis) and the Lone star tick (Amblyomma americanum).
To identify these tick you need to look at three structures. The
Scutum (shield shape) is found on the ventral (top) side of hard bodied
ticks. A dark brown or black scutum is found on Ixodes. A scutum with varied colors of tan, brown and black is Dermacentor. A scutum with a yellow spot is Amblyomma. Festoons are a segmented patterns found on the edge of Dermacentor and Amblyomma, but not Ixodes. Another prominent feature to use for identification is the shape of their mouth parts, or capitulum. The Dermacentor has a shorter length capitulum compared to Ixodes or Amblyomma. An excellent site to see more details for identification can be found at the TickEncounter Resource Center.
The tick’s mouth area, or Capitulum, has three parts.
The hypostome is a long tubular shape structure that works like a
hypodermic needle and is inserted into the prey. Attached to the
hypostome are Chelicera that look like small claws and are used to grasp
the skin on the prey. Two outer appendages called Palps are used to
close onto the skin to hold the tick in place. The tick inserts the hypostome into the skin and expels saliva
that contains substances to help in sucking in blood. An analgesic
compound is injected to suppress pain or itching, a vasodilator to
increase blood flow into wound area, an anticoagulant is added to
prevent clotting, a metalloprotease is used to breakdown tissue (works
like a meat tenderizer), and a cement is secreted to solidify the
attachment into the skin. Once the bite has been set then the tick draws
in whole blood through the hypostome. Feeding will take several days to
complete. Only the adult female will engorge with blood, all other life
stages of the tick will regurgitate to maintain a healthy fluid
balance. The tick will take in blood, separate the cells and serum
proteins and then regurgitate the remaining fluid back into the wound.
The regurgitation is important to flush out excess fluid from the tick,
plus the passage of fluid back through the mouth will pick up additional
tick saliva to maintain the wound site for continued feeding. It is
through this process that ticks are able to transmit diseases. As ticks
draw up blood during feeding, they can pick up pathogens from an
infected host. When ticks regurgitate fluids they can inject pathogens
into the wound site.
Life Cycle of Ixodes
Ixodeshave
a two-year life span marked by four stages of development beginning
with eggs. The second stage involves eggs hatching into larvae early in
the spring. As the tick ages and progresses from one life stage to the
next it matures through a process called metamorphosis. During
metamorphosis the tick will molt, shedding the skin and scutum during
this process. Surprisingly, ticks will only take three blood meals
during their lifetime. These blood meals drive the molting process.
During the period between molts the tick is morphing; it reduces
physical activity to sustain life while devoting energy reserves to
growth and development between the long stretches in feeding. Extensive
stress from not feeding can cause a diapause, wherein development is
suspended and activity is reduced to minimum levels. Diapause can prove
to be a practical survival mechanism; if the tick doesn’t successfully
feed, the tick could live longer than two years and gain additional time
to complete its life cycle.
Stage
1 of the tick’s life cycle, beginning with eggs, is shown in the photo.
Eggs can be reddish to black in color, are often translucent, and look
like miniature caviar.
An adult female Ixodes scapularis and a clutch of eggs. (Photo credit: James Gathany, CDC Public Health Image Library)Ticks
must stash their eggs in locations that provide protection from harsh,
low temperatures in the winter, so they will usually bury a clutch of
eggs underneath the duff, the composting material on the ground. The
eggs are small, only about 3 millimeters and have a sticky texture.
Ticks have a limited ability to move, so storing the eggs near their
first blood meal improves chances of survival when they hatch. Animals
that brush by the clutch might pick up some eggs in their fur which
provides a method to spread to other areas and, fortuitously, they are
attached to their next blood meal.
Stage
2 of the tick life cycle begins when the eggs hatch in the spring,
producing a large litter of as many as 3000 larvae. The larvae are very
small, similar to the size of the eggs and about the size of a poppy
seed. Larvae have only six legs with limited mobility. They are starved
for nourishment and will immediately proceed to hunt for a blood meal.
Since size and the reduced number of legs limit mobility, larvae will
not be ambitious in scaling higher up in the foliage. Instead, they keep
to low growing grass or foliage and are, therefore, more likely to prey
on small animals that also keep to ground level. Since their hunting
strategy is to ambush, obtaining a blood meal can pose difficulties;
because the animal needs to walk into the tick to become a victim, the
probability of being in the right location to get a needed blood meal is
very low and could take the entire spring, summer and fall seasons.
Most of the ticks will die at this life stage. The successful larvae
will return to the ground duff after feeding to molt over the ensuing
winter.
If the larvae make a chance encounter with a host, such as a white footed mouse (Peromyscus leucopus) and, if this host was carrying Borrelia burgdorferi, the bacteria responsible for Lyme disease,then the larvae become infected. This initial blood meal is the first chance that a tick can become infected with Borrelia.
How Ixodes transmit Borrelia burgdorferi (Bb) between hostsStage
3 of the tick life cycle begins in the spring when the larvae have
successfully morphed into nymphs. These nymphs emerge from their winter
metamorphosis ready to seek a second blood meal. Nymphs are slightly
larger than the larvae, about the size of a sesame seed, and have grown
two more legs. Their extra legs and size allow nymphs greater mobility
and as a result nymphs can climb higher into the foliage to prey on
larger animals. Nymphs successful in obtaining a blood meal then take
refuge in the ground duff to molt into adults through late spring and
summer.
During Stage 4, the adults emerge in the fall in search of a blood meal to gain energy for mating. The mating process occurs while the ticks are still on their last feeding host. Both
the male and female must encounter each other on the same host. Then
the female will engorge with blood over a period of 8-10 days,
increasing about 20 times in size. Once fully engorged, the female will
then drop off of the host to find a location to lay eggs and complete
the tick life cycle.
A Day in the Life of a Tick
Whenever
possible, ticks reduce activity and move only when essential.
Interestingly, ticks can reduce breathing to once per day, a sign of the
low demands of their physical activity. A typical day for a tick begins
in the morning when it emerges from the ground duff and soil to climb
up blades of grass or bushes. After finding a strategic position to
perch, the tick will lie in wait for the opportunity to ambush a host.
In a process called questing, the tick extends its front legs as a snare
to grab an unsuspecting animal as it walks by. During the quest, ticks
will remain inanimate for extended periods of time without moving. If
the tick fails to grab onto prey during the day, it will return to the
moist protection of the ground duff during the evening. From early
spring through late fall, ticks can be found questing in grass and low
brush.
Ticks
are particular about the outside conditions and only emerge under
hospitable weather conditions. They avoid water and rain. They also seek
refuge from excessive heat and low humidity, hence they are more likely
to be found in shady areas, and during the morning or late afternoon
when the sun is lower in the sky.
To identify these tick you need to look at three structures. The
Scutum (shield shape) is found on the ventral (top) side of hard bodied
ticks. A dark brown or black scutum is found on Ixodes. A scutum with varied colors of tan, brown and black is Dermacentor. A scutum with a yellow spot is Amblyomma. Festoons are a segmented patterns found on the edge of Dermacentor and Amblyomma, but not Ixodes. Another prominent feature to use for identification is the shape of their mouth parts, or capitulum. The Dermacentor has a shorter length capitulum compared to Ixodes or Amblyomma. An excellent site to see more details for identification can be found at the TickEncounter Resource Center.
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