• by Dr. Sarah D. Oktay – Director, University of Massachusetts Nantucket Field Station •
As tourists and summer residents start streaming back to the island, Nantucketers are emerging from our hobbit holes to bask in the sunnier and warmer days like a pack of painted turtles and all this new outdoor activity means it is time to be aware of and check for black legged ticks. Spring can be one of the most likely times for you to encounter a tick. Our warm bodies are easier to distinguish against the cooler air, hungry ticks are looking for a warm host and we are out and about on the trails providing a moving picnic. Early May used to be the bellwether month for warning people to watch out for ticks but scientists now recommend that we start education in early April as warmer weather begins to occur earlier each year on average. When deer ticks are born in early summer they do not carry any diseases yet, but the nymphal ticks that peak in May carry the majority of the disease since they have had time to interact with various other hosts like rabbits and white footed mice that carry the bacteria (organisms) that transmit Lyme, babiesiosis and Anaplasmosis.
Ixodes scapularis (often known locally as Ixodes dammini) are accurately called blacklegged ticks or more commonly known as deer ticks and they take two years to complete their life cycle. Ixodes scapularis is approximately 3 mm in length. Females have a black head and dorsal shield, and a dark red abdomen. Males are entirely black or dark brown. Both sexes have eight legs that are black (not an insect, an arachnid more closely related to spiders). This black legged tick also has a characteristic anal opening, which appears within a horseshoe-shaped ridge on the lower edge of the abdomen, on the ventral side. Not that you are looking for that. Deer ticks, unlike other ticks, do not have festoons (ridges on the edge of the lower abdomen). Sounds festive, it’s not. In the larval state, black legged ticks have a dark head, with a translucent body. Like the adult, the nymph has four pairs of dark legs, but is smaller, measuring at about 1-2 mm in length.
Their distribution across the Unites States is often linked to the distribution of its primary reproductive host, the white-tailed deer although there are dry areas of the country with plenty of deer and no deer ticks. Here on Nantucket we find them in our sandplain grasslands, old agricultural fields, heaths and moors, scrub oak forests, and rarely in the salt marshes. Ixodes scapularis is parasitic throughout its life on the white-footed mouse, small mammals and birds, and the white-tailed deer. In addition to being a parasite, I. scapularis is also a vector of Lyme disease, caused by Borrelia burgdorferi. Borrelia burgdorferi is a bacterial species of the spirochete class of the genus Borrelia. This tick (Both nymph and adult stages) is also known to be a vector of human babesiosis, Babesia microti, and human granulolytic erlichosis. Good times. But don’t panic, you can take plenty of precautions and still enjoy the outdoors.
Adult males and females are active October-May, as long as the daytime temperature remains above freezing. Preferring larger hosts, such as deer, adult blacklegged ticks can be found questing about knee-high on the tips of branches of low growing shrubs or high grasses. Adult females readily attack humans and pets. When they are fat and happy as adults they are much easier to spot and more likely to be noticed and removed before they have attached and transferred any pathogens they may carry. Once females fully engorge on their blood meal, they drop off the host into the leaf litter, where they can over-winter. Engorged females lay a single egg mass (up to 1500-2000 eggs with 810 being the average number) in mid to late May, and then die. Larvae emerge from eggs later in the summer. Blacklegged ticks are easily distinguished from other ticks by the orange-red body surrounding the black scutum. Scutum, although it sounds rude, is the Latin word for shield. In our use here it refers to the shield-like part of the tick’s body right behind the head. You can get a great idea of what different tick species look like on the University of Rhode Island’s Tick Encounter Resources Center web site http://www.tickencounter.org/tick_identification/guide (accessed May 1, 2015).
Males usually do not feed, they don’t need to beef up to feed babies, which is very different from their human counterparts. They also die after mating. Altogether this does not sound like an ideal life although they do continue mating long after actually transmitting sperm, which may be that whole “anticipating dying part” if they believe other tick rumors.
Nymphs are active May-August, and are most commonly found in moist leaf litter in wooded areas, or at the edge of wooded areas. The eight-legged, pin-head sized nymph typically attaches to smaller mammals such as mice and voles, requiring 3-4 days to fully engorge. Nymphs also readily attach to and blood feed on humans, cats and dogs. Once fed, they drop off into rodent burrows or leaf litter in animal bedding areas where they molt and emerge as adults in the fall. The sneaky nymphs are the ones you have to be on the lookout for right now. They are tiny. The best defense is to check yourself out thoroughly when you return from a dog walk or hike, and to wear light colored clothing. Big sprays containing DEET will work too but have many serious side effects both to us and the environment. I wear a variety of organic natural sprays many of which are available from island and Cape merchants. I am field testing Aromaflage right now and also like Ecosmart. Stop by the Field Station to test drive various organic sprays.
The six-legged (Sneaky!!) larvae are active July-September and can be found in moist leaf litter. Larvae hatch nearly pathogen-free from eggs (only Borrelia miyamotoi is known to infect blacklegged tick larvae), and remain in the leaf litter where they will attach to nearly any small, medium or large-sized mammal and many species of birds. Preferred hosts are white-footed mice. Larvae remain attached to their host until replete (full), which usually requires 3 days. Once fully engorged, the larvae drop off of the host and molt, re-emerging the following spring as nymphs (and with two extra legs-quite a trick).
Back to our issues with climate change and how the warming temperatures are moving tick season up earlier and earlier each year, Dr. Richard S. Ostfeld, is a disease ecologist at the Cary Institute of Ecosystem Studies in Millbrook, NY, and he has been coming to Nantucket along with many other tick borne disease experts to evaluate how climate change may be effecting the incidences of tick borne diseases
According to Dr. Ostfeld and others, if we want to get a leg up on tick-borne illness we need to become vigilant earlier in the season. “Results on the trend toward advanced spring emergence were published this February in the journal Philosophical Transactions of the Royal Society B. Among the paper’s findings: nymphal ticks peak in the spring, larval ticks peak in the summer, and both emerge nearly three weeks earlier in warmer years. As a result, Ostfeld is advocating moving Lyme Disease Awareness month to April. “By encouraging safe behavior, public education campaigns play a real role in reducing the number of people that suffer from Lyme disease and other debilitating tick-borne illnesses. In New York State – and likely throughout the Northeast – we need to begin taking preventative measures before May, as potentially infected nymphal ticks are already on the move. Research conducted in Nantucket, Massachusetts suggests that educational interventions can lower the incidence of Lyme disease between 20% and 60% depending on the length of time people spend outdoors in areas where ticks are active ” (from http://www.eurekalert.org/pub_releases/2015-04/cioe-ttm042715.php accessed April 29, 2015).
Even without a host, deer ticks are able to survive for roughly three months. This is particularly evident during the winter. As the cold weather begins to take hold, deer ticks who have not found a host will take refuge in areas that are high in vegetation. They will remain inactive until late February or early March, at which point they will die if they fail to find a host.
A cold winter can drastically reduce the tick population as a deer tick can only survive if the average winter air temperature is 19 degrees or warmer. Unfortunately, global warming is expanding the range northward of the deer tick, as scientists have recently discovered, they have managed to survive for the first time as far north as Isle Royale in Lake Superior, located off the coast of northern Minnesota (http://www.startribune.com/lifestyle/health/125511433.html?refer=y accessed April 22, 2013). This last winter, although snowy, storm ridden, and long, was not as cold as it felt. A harsh cold winter does not mean that the ticks were killed off, if it is super cold and very dry and icy, that might be the case, but according to Dr. Ostfeld, all that snow serves an insulating effect that can be protective for ticks. And snow is an indicator of warming temperatures that can support that moisture versus true arctic cold which is a drier cold.
According to the Animal Diversity Web “http://animaldiversity.org/accounts/Ixodes_scapularis/ accessed May 1 2015: “Habitat and microclimates are still crucial in the establishment and survival of this tick species. Even in areas of high deer population, the deer tick may not be found. Moving towards 175 m elevation, populations decline. In addition to elevation, coastal proximity is important. Ixodes sculparis seems to thrive in humid environments, and may also be assisted through dispersal by neotropical songbirds that are migrating in/through the area. Ixodes scapularis is very rarely affected by predators. Due to its small size, this tick is rarely targeted or found by birds or other possible predators. Instead, it is highly affected by density-independent factors such as climate with temperature and humidity changes.”
People on Nantucket and our local physicians and hospital employees are very well informed about Lyme disease and other tick borne diseases. But don’t let that good education effort fool you, if you live in NY, CT, MA, RI, you can interact a deer tick too, they just get more press here. They are found throughout most of the US although they are most commonly east of Texas. The geographic range of Ixodes scapularis, the deer tick or blacklegged tick, consists of North America as a whole, also known as the Nearctic region. This includes the eastern coast of the United States, westward towards Texas, and northward into Minnesota. These ticks are also found in southeastern Canada, and northern Mexico, but it is very rare to find I. scapularis past these borders.
You may not know it but the UMass Boston Nantucket Field Station has hosted for over thirty years the prominent tick borne disease expert, epidemiologist and Professor in the Department of Infectious Disease and Global Health at Tufts University, Dr. Sam Telford III who has been researching tick-borne disease and its effect on humans and animals on Nantucket since 1984. Dr. Telford has some good advice regarding simple precautions to take to lower your risk of catching a tick borne disease. One of the best ways to easily see and remove ticks is to wear light clothing, long sleeves and pants. Use bug repellent if you know you’ll be in tick habitat primarily spraying just your legs and ankles. After you come inside, do a total body tick check. When you want to be really cautious, you can always tuck your pant legs into long socks. If there’s anything unusual, see a doctor. If you have an inexplicable fever in the summer, bring that to the attention of a doctor. From an interview with Dr. Telford a few years ago “I’ve been working with these diseases for years, and I’m disease-free. I might get a few bites a year, but the never stay on for longer than a few hours-and that’s not enough time for them to do damage. Ticks need to feed at least 24 hours before they can transmit the pathogens that cause Lyme disease, babesiosis, or ehrlichiosis.” http://enews.tufts.edu/focus/19/2007/09/04/WhatMakesHimTick.
Learn more about ticks at the Center for Disease Controls web site http://www.cdc.gov/ticks/life_cycle_and_hosts.html. I also recommend this blog http://dujardindesign.com/blog/tag/environmental-awareness/ and last but not least, on your property try Damminix tubes to reduce the number of ticks near your home (http://www.ticktubes.com/).
