Ticks are small parasitic organisms that feed on the blood of mammals, birds, and reptiles. They are known to spread diseases like Lyme disease, Rocky Mountain spotted fever, and ehrlichiosis. Understanding what scents and cues attract ticks to potential hosts can help people take precautions against tick bites when spending time outdoors.
Carbon dioxide
One of the main scents that attract ticks to hosts is carbon dioxide (CO2). Ticks locate hosts by detecting increases in carbon dioxide in the air. Mammals and birds release carbon dioxide as they exhale, so ticks use this scent as a cue that a potential host is near. Studies have shown that ticks move toward sources of carbon dioxide gas and can detect very slight changes in CO2 levels.
Ticks locate carbon dioxide plumes through special receptor cells called haller’s organs. These sensory organs are located on the front legs of ticks. When the tick detects an increase in carbon dioxide, it will orient itself toward the host by moving against the concentration gradient of carbon dioxide. The tick uses the scent of CO2 to determine the direction of a potential host.
Since carbon dioxide is one of the main attractants for ticks, they are often more abundant on game trails and in areas with high foot traffic. The accumulated breaths of passing mammals makes these areas rich in carbon dioxide. Ticks will perch themselves on the tips of grass and vegetation along game trails to latch onto passing hosts.
Using carbon dioxide to bait ticks
The strong attraction of ticks to carbon dioxide has been used to bait and trap ticks for research purposes. Dry ice is a convenient source of carbon dioxide that researchers use to attract ticks. Dry ice releases CO2 as it undergoes sublimation, so simply placing containers of dry ice in tick-infested areas will begin drawing ticks toward it.
Tick traps made with dry ice are a common research tool for sampling tick populations. The device collects attracted ticks in a container for counting and identification. Dry ice traps provide an efficient method to monitor tick abundance and surveillance for tick-borne diseases. The scent-baited traps collect a representative sample of the tick population without having to tediously search through vegetation.
Body heat
In addition to carbon dioxide, ticks also use body heat as a cue to locate hosts. Warmblooded mammals and birds generate heat that ticks can detect through infrared radiation. As with carbon dioxide, ticks will orient themselves toward the temperature gradient emanating from a potential host. Body heat helps ticks pinpoint the location of the host once they detect an increase in carbon dioxide.
Ticks detect infrared radiation through special black-colored pits located around the Haller’s organs on their front legs. These infrared heat sensors allow ticks to hone in on the exact location of the host’s body once the CO2 scent plume brings them closer. Body heat detection explains why ticks often attach themselves to the warmest parts of the host’s body, like the head, neck, and groin area.
Using body heat to attract ticks
Similar to carbon dioxide, body heat can also be used to bait ticks in research settings. Heated surfaces and infrared beams of light have been used to attract ticks to traps. The warmed areas simulate the body heat of hosts. One study in Italy used heated plates to collect questing ticks in the environment. This method was successful for trapping multiple tick species without any chemical attractants.
However, carbon dioxide is a stronger driver of tick attraction than heat alone. Traps baited with CO2 collect many more ticks than heat by itself. The combination of carbon dioxide plus infrared heat offers the most powerful lure for maximizing tick trap productivity.
Octenol
Octenol is another scent produced by mammals that ticks use to locate hosts. Octenol is a chemical compound, specifically a volatile aliphatic alcohol, that is emitted in exhaled breath and skin odors of animals. Cows and horses give off high amounts of octenol, making them especially frequent targets of tick bites.
Tick species such as Amblyomma americanum (lone star tick) and Dermacentor variabilis (American dog tick) are particularly sensitive to octenol and will orient toward sources of this scent. Octenol helps attract ticks to their hosts from longer distances before they can detect carbon dioxide and body heat.
Interestingly, the presence of octenol inhibits the attraction effect of carbon dioxide for certain tick species. When both scents are present, the ticks will move toward the octenol rather than CO2 source. The inhibitory interaction suggests that octenol is a dominant tick attractant for mammals like cattle that produce large quantities of it.
Using octenol-baited traps
Like carbon dioxide, scientists leverage the attraction of ticks to octenol by using it as bait for trapping ticks. Cotton wicks or small vials containing octenol are placed in tick traps. The smell helps lure ticks toward the trap. Octenol-baited traps are best suited for collecting ticks that feed on hoofed mammals where octenol presence is highest.
However, the effectiveness of octenol-based traps can vary across geographic regions. Attraction to octenol seems to differ between tick populations based on local host animals and environmental conditions. In certain areas, octenol does not attract more ticks than unbaited traps. Research suggests combining octenol with carbon dioxide provides the most consistent results for maximizing tick trap yields.
Ammonia
Ammonia is another chemical attractant that can lure certain tick species. Ammonia is emitted in sweat and bodily waste products of many mammals. As a result, ammonia serves as an additional scent cue associated with potential hosts. Some important tick carriers of disease like Ixodes scapularis (blacklegged tick) demonstrate attraction to ammonia odors.
In laboratory studies, ticks exposed to ammonia gas will orient themselves toward the source. Tick activity and attraction is strongest at specific concentrations of ammonia around 5-10 ppm (parts per million). Interestingly, high concentrations of ammonia beyond 30 ppm have a neutral or repelling effect on ticks.
The sensitivity to ammonia varies across tick species. It seems to be an important attractant for ticks that feed on rodents and other small mammals where ammonia levels are higher. Deer ticks rely more on carbon dioxide to locate larger hosts like deer.
Using ammonia to bait ticks
Field researchers haveexperimented with using dilute solutions of ammonia to bait tick traps. Cotton rolls soaked in ammonia can help attract certain ticks like the blacklegged tick. However, carbon dioxide typically outperforms ammonia at drawing ticks in real-world conditions.
The concentration of ammonia must be within the ideal range to maximize attraction. Too little ammonia is ineffective, while too much can repel ticks. More field research is needed to determine optimal protocols for using ammonia as bait for trapping disease-carrying tick species.
Animal odors
In addition to specific chemical compounds, ticks also respond to host-associated odors. Smells emitted from the skin, fur, and waste products of animals can attract ticks looking for a blood meal. Ticks pick up on the characteristic mix of smells produced by different host species.
Studies have shown that extracts taken from animal fur contain odorants that tick antennae are highly sensitive to. For example, odors collected from mice and rabbits trigger strong electrical signals in tick sensory cells. Certain tick species can even distinguish between different types of host animals based on their signature smells.
Animal odors seem to be more important for ticks that show high host specificity, such as rabbit ticks. Generalist ticks that feed on multiple host types may rely more on basic scent cues like carbon dioxide. But odors help ticks identify preferred host targets before committing to latching on for their meal.
Using host-based odors to attract ticks
Odor extracts from different animals have been incorporated into traps as attractants for ticks that target those particular hosts. Some examples include:
- Rabbit odor extracts to attract rabbit ticks (Haemaphysalis leporispalustris)
- Rodent odors collected from bedding to attract ticks that feed on mice and voles
- Sheep wool odors to attract sheep tick species
Using the odor profile of the tick’s preferred host can help maximize trap effectiveness and target specificity. The host-derived compounds attract the ticks that are most likely to be carriers of pathogens affecting that animal.
Can humans smell what attracts ticks?
For the most part, the chemical scents that attract ticks to hosts are odors that humans cannot detect. Carbon dioxide, octenol, and ammonia have no perceptible scent to people at the concentrations ticks sense them.
However, some host odors that appeal to ticks may align with smells that humans associate with animals. For example, compounds in rabbit fur extract that attract rabbit ticks include hexanal, 2-hexenal, and nonanal. These are grassy, fatty aldehyde compounds that contribute to the characteristic smell of animals.
While humans can recognize the general smell of animals, we cannot discern the specific odorant blend that ticks detect. So we cannot rely on our nose to identify what scents are attracting ticks to us or repelling them.
Do scented products help repel ticks?
Certain strong odors may help mask human scent and potentially deter tick bites while outdoors. Examples of scented repellents include:
- Citronella oil
- Peppermint oil
- Cedar oil
- Lemongrass oil
- Geraniol
However, there is limited scientific evidence that these artificial scents are effective at driving away ticks. Any repellent impact likely depends on masking the attractant odors like CO2 that draw ticks to humans.
Plant-derived repellents containing oils work best at very close range where the smell is strongest. But they may quickly diffuse and lose potency under natural conditions outdoors. Heavier smells also dissipate in the breeze.
Strong fragrances can overwhelm human scent to some degree, but ticks will still detect us through exhaled carbon dioxide if we are close enough. The artificial odors have not been shown to be comparable to formulations containing DEET or picaridin for repelling ticks.
Can ticks smell blood?
Surprisingly, ticks do not actually seem attracted to the scent of blood itself. Since they feed exclusively on blood, one might assume blood odor would attract hungry ticks.
However, laboratory experiments testing ticks’ response to whole blood and plasma show that blood-derived compounds have no attractive effect. Blood metabolites actually tend to inhibit tick activity. It appears that ticks instead rely on host cues like CO2, heat, and odors to find hosts, not actual blood scent.
Once attached to the host’s skin, a feeding tick can detect blood compounds through its Haller’s organ. But blood components do not serve as an attractant. This makes sense evolutionarily, since hunting by blood smell would not help ticks locate hosts. They need to pick up on broader host cues like carbon dioxide plumes instead.
Do ticks attract other ticks?
Ticks release an aggregation-attachment pheromone that helps other ticks locate the same host. After attaching, ticks secrete a chemical that encourages other ticks to cluster together at the feeding site. This results in groups of ticks feeding in close proximity.
Certain compounds in tick saliva and feces activate this aggregation response. Ticks of the same species detect these secretions, causing more ticks to aggregate and feed on the animal. The clustering likely provides survival advantages against host grooming and removal efforts.
However, the aggregation pheromones only work at very short distances after ticks have already settled on the host. They do not attract ticks independent of the other host-emitted cues. Pheromones are not a long-range attractant, but rather facilitate group feeding once a host is found.
What scent do ticks dislike?
While the attractant scents that draw ticks to hosts are well studied, less is known about odors that repel ticks. Limited research suggests some potential tick repellent scents include:
- Lemongrass oil
- Cinnamon oil
- Clove oil
- Eucalyptus oil
- Lavender oil
One study found that lavender oil demonstrates both repellent effects and insecticidal activity against ticks. The active compounds linalool and linalyl acetate may impact tick odor receptors and deter feeding.
Extracts from the American beautyberry shrub have also shown tick-repelling properties in lab trials. Other plant oils and extracts may interfere with the scent signals ticks use to locate hosts.
However, most scent-based repellents provide fairly short-term protection that diminishes outdoors. More research is still needed identify odors that effectively disrupt tick host seeking behavior for prolonged duration.
Conclusion
Ticks rely predominantly on sensing carbon dioxide, heat, and certain odor molecules to detect potential hosts nearby. By recognizing these signature scents, ticks can identify optimal places to wait for a blood meal, like along game trails and forest edges.
Carbon dioxide from breath and odor cues from skin and fur provide the primary attractant signals. Body heat helps ticks hone in once close by. Specific scents like octenol and ammonia also attract some tick species.
While certain strong odors from plants may offer some repellent effects, more work is needed to understand what scents deter tick feeding and attachment. Avoiding the smells ticks associate with hosts remains the best way to evade them.