Legend says that a stake in the heart will kill a vampire. But it’s a bit trickier if you’re plagued – as moose can be – by tens of thousands of tiny bloodsuckers.
In the case of moose, vampires are winter ticks (Dermacentor albipictus), and finding a way to stake them was tricky. However, recent research has found a potential – and microscopic – vampire hunter.
Winter ticks are a single-host parasite, which means that all three active stages – larvae, nymphs and adults – feed on a single host animal. This species prefers to feast on ungulates and is often referred to as the “moose tick” because, unlike deer, moose are unable to remove ticks through grooming, making them particularly vulnerable to heavy loads of ticks. ticks. The average number of ticks on a single moose can hover around 47,000, with high counts exceeding 96,000.
That many ticks can drain a calf’s blood in two to three weeks. From 2017 to 2019, researchers from the Vermont Cooperative Fish and Wildlife Research Unit at the University of Vermont noted a 91% mortality of moose calves in Vermont. And from 2014 to 2016, researchers from the University of New Hampshire’s Department of Natural Resources and Environment observed 70% mortality in northern New Hampshire and western Maine due to winter ticks.
Such alarming mortality rates have raised concerns among wildlife management officials about the health of New England’s moose population. However, due to the life cycle of ticks, it has been difficult to find a management strategy for winter ticks.
Foraging for winter tick larvae – or finding hosts – from late summer through fall. After attaching to a host, ticks feed, molt and mate on the same animal during the winter. When adult female ticks are maximally engorged, usually between March and May, they fall to the ground. During the summer and early fall, the females lay eggs and die, then the larvae emerge and hang around at ground level and begin to search again.
Due to their single-host nature and the timing of their life cycle, the winter tick population depends on abundant hosts and a window of time in the fall to find one. Limited hosts, cold fall temperatures and early snow will inhibit ticks – but these are all conditions that are impossible to manage in favor of moose.
Enter Cheryl Sullivan, entomologist at UVM’s Entomology Research Laboratory. She leads a project to study entomopathogenic fungi as potential allies against the winter tick. These fungi consume arthropods like insects, spiders, and yes, ticks.
Entomopathogenic fungi are found naturally in soils around the world and infect hosts through airborne spores. When a spore lands on a tick, it germinates, punctures the tick’s outer shell, and then spreads its hyphae — the threads that make up the mycelium network of fungi — through the tick’s body. Like in a horror movie, the growing fungus tears through its host’s internal organs and produces toxins, which eventually kill the host. Fruiting bodies emerge from the host, releasing more spores.
Sullivan and the UVM team tested fungal strains of Metarhizium anisopliae and M. brunneum against winter ticks. Some strains are already commercially available for residential insect and mite control, and some have been isolated from northern Vermont forest soils. While commercial strains were the most effective, Sullivan found that in lab experiments, a local strain killed 89% of tick larvae within three weeks.
UVM researchers are particularly interested in exposing ticks to fungal spores at the larval stage, before they have found a host. This is the phase where the winter tick is most vulnerable: the larvae live in the fungi’s natural home (soil and leaf litter), and both need similar moist conditions to thrive.
Deliberately exposing ticks to specific fungal pathogens in their environment is a more sustainable alternative to chemical pesticides, although not without challenges. As Sullivan explains, “entomopathogenic fungi require specific environmental conditions, including temperature and humidity, extensive spore contact with a host, and appropriately timed applications at a susceptible life stage for their use. be effective”.
Spreading fungal spores wherever moose live is impractical, so moose advocates should target locations that Sullivan describes as “localized areas of optimal habitat where moose are known to congregate and be prone to winter recruitment of ticks.
While researchers are still evaluating the possibility of using entomopathogenic fungi to attack winter ticks, it’s good to know that when moose are confronted by swarms of miniature vampires, they could be aided in battle by hunters. microscopic vampires.
Rachel Sargent Mirus lives in Duxbury. The Outside Story is attributed to and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of the New Hampshire Charitable Foundation.