Ticked off

Many American homeowners clear their lawns of fallen leaves in autumn to avoid creating tick-friendly habitats. But a new study says that raking or blowing leaves just out to the forest edge isn’t enough, as it could increase tick abundance and risk of bites.

For most of us it’s no big deal to play host to a tick taking a blood meal – which it does two to three times during its life cycle.

Most bites result in little more than swelling and redness at the bite site, although some people have more severe experiences, such as tick paralysis and allergic reactions including anaphylactic shock. 

In some cases, ticks can pass on some pretty nasty diseases, including tick typhus in Australia’s Queensland, and the debilitating Lyme disease-like syndrome.

All up it’s a good idea to avoid the little arachnids, and the new research, published in the Journal of Medical Entomology, offers a new idea to people whose homes border tick-friendly bushland.  

In areas of the US where ticks that carry Lyme disease-causing bacteria are prevalent, residential properties often border forested areas, and blacklegged ticks (Ixodes scapularis) thrive in the “edge habitats” where lawn and woodland meet. 

Blowing or raking leaves from lawns and gardens to these edge habitats can triple blacklegged tick numbers the following spring, says study co-author Robert Jordan, from the Monmouth County (New Jersey) Mosquito Control Division.

Jordan and co-author Terry Schulze, a medical entomologist, ran three test plots in residential New Jersey in 2017 and 2018. Each had areas at both the forest edge and deeper within the wooded area. 

Some edge plots were allowed to accumulate leaves naturally, while others received additional leaves via periodic raking or leaf blowing. The “managed” edge plots resulted in leaf-litter depths two to three times that of the natural edge and forest plots. 

The researchers then compared the presence of nymphal (juvenile) blacklegged ticks in the test plots the following spring. In both years, the number of blacklegged tick nymphs in the managed edge plots was approximately three times that of the natural edge and forest plots. 

“While we expected to see more ticks along lawn edges with deeper leaf-litter accumulation, we were surprised about the magnitude of the increase in ticks that resulted from leaf blowing or raking,” Jordan says.

Fallen leaves provide blacklegged ticks with suitable habitat via higher humidity and lower temperatures within the leaf litter, as well as protection from exposure over winter.

“The thing homeowners need to keep in mind is that accumulations of leaves and other plant debris provide ideal host-seeking and survival conditions for immature blacklegged ticks,” says Jordan.

Previous research in the US has shown that people more commonly encounter ticks on their own properties than in parks or natural areas. Jordan says that’s the major reason why he and Schulze have been evaluating a variety of residential tick-prevention strategies in recent years. 

They suggest homeowners remove leaf litter altogether (through a “green bin” program, if available), compost them, or put them further away from high-traffic areas on their properties.

“On properties with considerable leaf fall, the best option would be complete removal of leaves from areas most frequently used – such as lawns, outdoor seating areas, and in and around play sets,” Jordan says.

“If this is not possible or practical, leaf piles should be placed in areas least frequently used. Where neither of these options is possible, or where leaf fall is minimal, mulching in place may be a good option, since this encourages rapid decomposition of leaves, which may reduce habitat suitability for ticks.”