Whether conducting field work or simply enjoying your yard, being outside provides a variety of shared experiences. Unfortunately, one of these experiences is the very likely encounter with ticks. If you’re like me, you can’t help but feel your pulse quicken when you see these critters – and not in the lovestruck way.
I have vivid memories of leaving field sites and looking down at my pants to start the initial tick check only to feel my heart skip a beat at the horror of the army marching up my pants. Thousands of early life stage ticks all marching for the chance to access to my blood. Not quite the heady feeling lauded in song, prose and internet memes.
Despite this, I am going to invite you to explore a tick’s world and their role in our environment.
First, it’s important to recognize ticks for what they are: multi-legged arthropods that are more closely related to spiders than insects. They are parasitic on the blood of reptiles, birds and mammals in order to sustain themselves and reproduce [1]. Ticks are found in warm and humid environments across the world because they need moisture to maintain body water balance while searching for a host. The activity of locating a host is called questing, a word that seems far more benign than a comprehensive term for the ambush or active hunting strategy used depending on the species of tick [2].
While we may immediately think all ticks are the same, there are two taxonomic families which we can easily refer to as hard ticks (Ixodidae) and soft ticks (Argasidae) due to their differences in body structure. Most tick species have four life stages – egg, larva, nymph, adult – which correlates to a three-host life cycle [1, 2]. However, the hunting strategy (ambush vs active), host specificity (specialized vs generalized), and seasonality of activity for each life stage affect the likelihood of encountering a tick [2, 4]. For this reason, it is important to be familiar with the species of tick where you live and how to identify them [2, 6].
Hard ticks – the ones we most commonly find on us and our pets – usually have two to three hosts through their life cycles and hosts tend to be different species [1]. For example, I live in the Northeast region of the United States where we are primarily concerned with contracting Lyme disease from the black legged tick, often called the deer tick, although it can carry several other diseases at the same time [3, 4]. The larval stage uses ambush questing on low vegetation to locate a small mammal or bird for the first blood meal. The nymph and adult stages of blacklegged ticks climb higher on vegetation to quest for larger mammals (i.e. deer, foxes, raccoons, opossums and humans) for their next blood meals [2, 3]. This is an example of a tick species that acts as a generalist parasite with the potential for spreading several diseases if it feeds on an animal, often referred to as the reservoir host, carrying the bacteria that causes lyme disease, Borrelia burgdorfer [4, 5, 6].
Our contempt for ticks is ultimately logical: ticks are the second most frequent vector of disease to humans (mosquitoes are first), and they are the most frequent vector of disease to domestic animals [1]. Admittedly, our feelings are ultimately misdirected. The thought of parasites tends to make us cringe because we don’t like the idea of being fed on and potentially receiving a disease in exchange for the sustenance our blood provides.
However, it’s important to remember that some parasites are the intermediary host, or vector, of the true source of disease – bacteria, viruses, or protozoans – which is the real cause for my rushing pulse when I see a tick [2, 5, 7]. We must also remember that we are not the only species affected by tickborne diseases; domestic pets can contract Lyme disease, and livestock populations can be drastically impacted [1, 2, 7].
It is all too easy in our human centric lives to think that eradicating a disease carrying parasite would be the obvious and most beneficial solution. Diseases, whether spread through parasites or direct transmission, are part of the competitive checks within our ecosystems – a literal example of “survival of the fittest.” Like predation, diseases remove the sick or infirm individuals and keep a population closer to the carrying capacity of the landscape [9]. Therefore, parasitic animals and the diseases they can spread serve as a natural method for keeping populations in check [9, 10, 11]. However, it is important to keep in mind that parasites and diseases are using other animals for food and shelter in order to reproduce; killing a host does not help them meet their objective [10].
Those that advocate for the conservation of parasites do not do so without acknowledging their negative impacts and do not fail to recognize the importance of eliminating some truly harmful parasites (like the Guinea worm). Rather, parasite conservationists argue we need to be careful about what we are willing to lose; removing a known parasite and the disease it carries could actually negatively impact human and environmental health [10, 11]. Parasite extinction may increase our exposure to an even more aggressive parasite and/or disease that we have less evolutionary history and contact with which can result in more damage than the original parasite/host relationship [10]. Additionally, parasites can be used as indicators of overall ecosystem health and human influence on the environment [12].
Maintaining healthy ecosystems is important for overall environmental health and mitigating the risk of parasites spreading diseases. There are a few natural predators of ticks – ants, spiders, birds, and a parasitic wasp – but their impact on a tick population is minimal given the fact that a female tick lays thousands of eggs [5, 8, 16]. Sustaining the predators of the animals that are reservoir hosts for tickborne diseases is a more productive way to reduce the chance of a tick feeding on an infected host [14, 15].
In the case of Lyme disease, the risk of getting bitten by an infected tick increases when there are abundant populations of small mammals, like chipmunks, shrews and the white-footed mouse, because they are reservoir hosts of the bacteria that causes Lyme disease and can feed numerous larval stage ticks [14, 15]. Several small mammal species, particularly the white-footed mouse, flourish in fragmented landscapes and forests that are not large enough to support small mammal predators; therefore, having the habitat to sustain foxes, barred owls, and other predators results in a natural check on reservoir host populations. Decreasing the number of small mammals then increases the diversity of hosts larval ticks are feeding on which ultimately decreases the number of ticks feeding on infected hosts. Therefore, maintaining a landscape that supports biodiversity decreases the risk of tickborne diseases[15].
Maintaining habitats that support a diverse animal population also increases the chances of ticks attaching to hosts that are less permissive of tick attachment and feeding [13, 14]. Opossums and squirrels are meticulous groomers and consume ticks they find hitchhiking on their bodies. Not our idea of a snack, but an excellent solution for these animals which can also benefit us humans. In fact, studies found squirrels and opossums consume 83 – 96% of the ticks that try to latch on and find a meal [13].
While I do not expect anyone to have discovered a fondness for ticks, it is important to understand how even a small parasite that we perceive as a nuisance has a role to play in our natural environment. Understanding tick and disease ecology is an example of a common experience that serves as an important starting point for learning how maintaining healthy habitat provides benefits to both human and animal health.
Call to action
As always, it is important to take steps to prevent ticks from biting you and your pets. There are also several ways you can manage your yard to decrease chances of picking up a tick hitchhiker. Also manage your yard to increase the biodiversity so that you are hosting ecological tick traps like opossums and foxes.
While I could not locate studies with specific numbers, chickens and guinea fowl consume various insects, including ticks, when allowed to forage through short grass. They may not have the largest impact on your local tick population, but if you are interested in keeping a coop this is an added benefit. Remember to check if your community permits keeping chickens before you start your coop!
Additional Resources:
CDC page on Preventing Tick Bites
CDC page on Preventing Tick Bites on your pets
Tick Management via Landscape Management
Citations
EcologicalEnigmas 