- July 6, 2017
Our yards and communities may be our sanctuaries; but, it is wise to remember that we share these spaces with a diversity of wildlife. Some of those species, like the black-legged tick (Ixodes scapularis and Ixodes pacificus)–often inaccurately referred to as a deer tick–can be carriers of infectious diseases such as Borrelia burgdorferi, the bacterium that can cause Lyme disease. Creating beautiful landscapes at home and in our community that support a diversity of wildlife while also minimizing our exposure to ticks requires us to understand tick ecology and design our spaces appropriately.
Ticks, like the one pictured below, like to reach out and touch someone for a delicious bloodmeal. They will climb grass, flowers, and trees, extend their front legs, and attach onto a passing mammal.
What ticks need to thrive and reproduce:
- Temperatures that are not too hot nor too cold.
- Thick leaf litter and/or moist ground cover to complete their multi-season, multi-year life cycle.
- Access to host blood meals; generally mice, squirrels, chipmunks, birds, opossums, raccoons, deer, and, inadvertently, humans.
To learn more about the ecology of ticks, explore this article.
Tick populations generally decrease when there are fluctuations in, or absence of, the environmental conditions mentioned above.
These can be manufactured by:
- Reducing moisture trapping debris in our lawns and flower gardens .
- Managing leaf litter.
- Supporting a variety of tick predators.
- Discouraging some animal hosts that provide blood meals for ticks.
- Removing invasive plants.
Lawn, free from leaf litter and cut short (one to three inches long), provides a less hospitable environment for ticks.open_in_new The short grass dries out quickly and does not hold moisture well, which is crucial for ticks’ survival. If you maintain a lawn, keep the grass cut short and leaf-free. Unfortunately, lawn maintained like this provides little habitat for other wildlife. An alternative to maintaining a lawn is transforming your lawn patches into mulched native flowerbeds.
Native flowerbeds, such as this one pictured with Jacob’s Ladder (Polemonium reptans) that use wood for mulch around plants, do not provide ideal habitat for ticks. Though there is no research we could find to date, common sense tells us that wood mulch holds less water and becomes much warmer compared to other mulch options. Ticks can find their way into flower beds if you have deer and mice visitors, but by using wood chips you will minimize the likelihood of ticks in your flowerbeds. Flowers have the added benefit of becoming spaces you don’t often walk through, making it far less likely you’ll pick up a tick there. Make sure to leave deadheaded flowers in the fall so the birds can eat the seeds in the winter!
Consider avoiding areas of your yard left to grow as native grasslands, such as meadows or prairies, in the spring/early summer and in the late fall/early winter when feeding ticks are the most likely to be questing (looking for a blood meal). You could also mow paths through these areas, such as this Habitat Network user has done, so that when you do travel through them, you are less likely to encounter a tick or brush against a blade of grass with a tick reaching out to grab-hold.
Leaf litter is favored by ticks because ticks are constantly combating desiccation. They cannot become overly dry in any of their four life-cycle stages, or they will die. Eggs are laid by females in leaves and in each lifecycle stage some time is spent by ticks in leaf litter. That is not to say ticks are not found in tall grass or other habitat, they are, as long as that habitat is moist enough to support them. Ticks will often utilize grasses and other foliage to climb up and gain access to a passing-mammal-blood-meal, but if the weather turns hot and dry, ticks will move towards the ground in search of dampness.open_in_new
This means that at home and in our communities we may be able to minimize tick populations by addressing leaf litter. One study removed leaf litter from a residential neighborhood from mid-March until mid-June when nymphal ticks are most active and nymphs were reduced in population by 72-100%.open_in_new Habitat Network, however, does not recommend removing all leaf litter from urban or suburban communities as a myriad of other organisms such as larvae of butterflies and moths use leaf litter as habitat. Some of these other organisms even include predators of ticks, such as wolf spiders.open_in_new
What we do recommend is moving leaf litter to areas of your property that is more than two meters (6.5 feet) away from places that you, your family, and your pets frequently spend time. Black-legged ticks quest, or travel short distances to find a blood meal. They don’t move more than one to two meters (3.2-6.5 feet) in any direction.open_in_new If you are able to remove leaves from frequently traveled outdoor areas you will minimize your contact with ticks.
Playing in leaves can be a lot of fun! We caution those that keep leaves on site to thoroughly check dogs, children, and adults who play in leaves after they are done. This activity is a fall classic in areas that have copious amounts of deciduous leaves in the fall. So enjoy! Just check yourselves afterwards.
Another option is to compost leaves with the help of earthworms. James Burtis, Ph.D candidate at Cornell University has found that the presence of invasive earthworms–which are prevalent in our gardens–may minimize tick populations.open_in_new
Earthworms (Lumbricidae), were eliminated in northern North American forests in the last glacial period.open_in_new These worms, however, do spread quickly in habitats in which they are introduced by humans. Though earthworms can be detrimental to the soil ecology in areas they are not native, there is evidence that in soil where earthworms are already found, they may help to minimize tick populations.open_in_new They assist in minimizing populations by shrinking tick habitat with fast leaf litter decomposition. Burtis et.al. found a 46.1% decrease in the density of black-legged tick nymphs and 29.3% reduction in black-legged tick larvae.open_in_new This was accompanied by an overall 69.9% reduction in all arthropods in soil microhabitatsopen_in_new along with earthworms causing an assortment of other unpredictable ecosystems changes.open_in_new Thus, though the presence of earthworms may show promise for decreasing tick densities, earthworms may also minimize the overall biodiversity of a soil ecosystem.
North American deciduous forests provide the soil microhabitat that ticks need to complete all stages of their life cycle. These forests have experienced various pressures over the last several hundred years influencing the ebb and flow of different species of plants and wildlife. In the last fifty years various invasive shrub species have come to dominate some forest understories, such as the Japanese barberry (Berberis thunbergii) pictured above. Scientists have examined the potential correlation between increased tick populations and invasive species of shrubs such as multiflora rose (Rosa multiflora)open_in_new, Eurasian honeysuckle (Lonicera spp)open_in_new, and Japanese barberry (Berberis thunbergii).open_in_new
A study conducted in coastal Maine compared the presence of ticks in forest understories dominated by Eurasian honeysuckle (Lonicera) and Japanese barberry (Berberis thunbergii)–pictured above–verses understory with eastern hemlock saplings.open_in_new Tick abundance was greater among the invasive shrub habitat. This finding is not surprising as barberry and honeysuckle shed leaves creating excellent leaf-litter mats and provide ideal habitat for deer, while the coniferous hemlock saplings provided less soil organic matter less ideal tick habitat.open_in_new
Multiflora rose (R. multiflora), pictured above, was also investigated for its role in maintaining tick populations. Test sites included patchy habitat dominated by multiflora rose and uninvaded forests free from the characteristic patchiness of R. Multiflora .open_in_new The leaf litter in the uninvaded forests was thicker than the patchy habitats created by multiflora rose, but the uninvaded forests had a greater density of ticks.open_in_new The percentage of ticks infected with B. burgdorferi, however, was higher in the multiflora habitat.
Perhaps leaf litter is the dominant factor favoring larger populations of ticks but the ecology of the fragmented patchy habitat of multiflora invasions may increase the percentage of ticks that become carriers of the Lyme disease-causing bacterium B. burgdorferi. This is likely due in part to the patchier habitat allowing host animals for the Lyme-causing bacteria–mice–to thrive.
Regardless of whether it’s the presence of invasive species of plants such as Multiflora rose, Eurasian honeysuckle, or Japanese barberry themselves, or other ecological conditions that influence increased numbers of ticks or more B. burgdorferi-infected ticks, removing invasives species of plants from properties is beneficial. Invasive species can create a cascade of ecological problems that we write about extensively here. Eliminating invasive plants and replacing them with native shrubs goes a long way to encouraging biodiversity while also potentially having the beneficial effect of lowering the number of infectious-disease-carrying-ticks. To learn more about native shrubs to consider, explore these two articles, winter berries and berries for your region.
Supporting rich, native biodiversity at all trophic levels may have a role to play in minimizing tick populationsopen_in_new–such as this pictured American Kestrel that has captured a white-footed mouse. The Ostfeld Lab at the Cary Institute of Ecosystem Studies is examining the dilution effect, where the greater the diversity of blood meals the ticks can find, the less likely they are to come into contact with white-footed mice (the primary vector of Lyme disease-causing bacteriumopen_in_new). Diversifying the menu options for ticks may dilute the blood meal pool.
Considering this dilution effect, property owners can provide habitat for a multitude of animals at home and in their community. Some of these animals have the added bonus of acting as predators of white-footed mice. Coyotes, foxes (pictured), and birds of prey will all help manage white-footed mice populations. Living in communities that encourage and support larger predators through the preservation of native green spaces or by creating patches, stepping stones, or corridors in a neighborhood may increase predators of tick-host rodents, thus minimizing tick populations over time. Ecological systems generally function best when biodiversity is present and encouraged.
Opossums (Didelphimorphia), it turns out, are effective killers of ticks with their elaborate grooming behavior. These North American marsupials eliminate over 90% of ticks that attach to them.open_in_new Though opossums are often written-off as being ugly or weird, in the discussion of Lyme disease they play a role in minimizing ticks in our communities. The Ostfeld Lab at the Cary Institute of Ecosystems Study estimates a single opossum can kill upwards of 5,000 ticks in one season.open_in_new Next time you see an opossum frozen on the side of the road, give it a wide right of way, as they are our allies in minimizing ticks populations.
How to I invite opossums into my yard?
Providing resources that opossums need to survive may help attract these tick-eaters to your property. Opossums are well adapted to living around humans as they are diet generalists eating fruits, nuts, grains, insects, slugs, snakes, frogs, birds, bird eggs, shellfish, mice, carrion, and scavenged trash. As nocturnal, solitary animals (except during reproduction) these animals will stay hidden in a den during the day and come out at dusk to forage. Providing abandoned burrows, hollow logs, tree cavities in snags, wood piles, or rock crevices might help provide shelter to neighborhood opossums.
Deer and mice, however, should be discouraged. There is a strong correlation between the presence of deer and the presence of ticks.open_in_new If you live in a community that permits hunting, humanely culling the herd once a year during hunting season may be a way to help control deer, and, indirectly, tick populations. There is no scientific consensus that hunting is a viable way to manage tick populations, but deer populations, specifically in suburban and urban areas are growing and ticks thrive where deer are present. If hunting is not permitted, discouraging deer in your yard by installing 10 foot high fencing, applying deer repellents, or adopting a dog who will startle deer that enter the yard, may help. Deer may be beautiful, but they are riddled with feeding and reproducing ticks, as pictured above.
Mice and other rodents should also be discouraged. If you own a bird feeder, make sure to keep the area under your feeders as free as possible of fallen seeds. Also, check out Project FeederWatch’s recommendations for deterring unwanted visitors to your feeders, like those pictured climbing up for a share of birdseed. Mice, chipmunks, and squirrels are all potential carriers of the Lyme disease-causing bacterium, Borrelia burgdorferi. Visiting your feeders puts them in close contact to your home, which may expose you and your family to ticks.
Trapping mice is another option, albeit one with its own ethical debate. In areas with very high incidence of Lyme disease there are efforts underway to figure out how to effectively manage mice populations (above, a researcher from the Cary Institute of Ecosystem Studies has trapped a white footed mouse to inspect it for ticks) . In one trial, bait boxes lure in mice and expose them to insecticides that kill ticks they may be harboring.open_in_new This is tricky business, however, since exposure to pesticides can lay the framework for resistance to insecticides in exposed populations. We write about some of these issues, here.
The good news is that managing for ticks encompasses many of the actions wildlife gardeners are already taking–eliminating invasive species, encouraging biodiversity by replanting with native plants, and supporting all trophic levels of wildlife. Taking a closer look at how properties manage leaves, grassy landscapes, deer, and mice populations are additional tools for minimizing tick-friendly habitat at home. The issue is complex and, as we warned, there are no silver bullets. Evidence does suggest that minimizing the conditions ticks need to survive, coupled with biodiverse landscapes, may help to keep these hardbodied Arachnids out of our sanctuaries.