Short Communication |
Corresponding author: Julie M. Ray ( teamsnakepanama@gmail.com ) Academic editor: Johannes Foufopoulos
© 2024 Julie M. Ray, Rowan M. Wergeland, Jeffery Karafa.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Ray JM, Wergeland RM, Karafa J (2024) Earthworms as a prey source for the insular snake Thamnophis sirtalis (Linnaeus, 1758). Herpetozoa 37: 197-200. https://doi.org/10.3897/herpetozoa.37.e123065
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Insular organisms typically evolve in closed, isolated systems; thus, changes caused by introduced species can drastically affect their ecology. Isle Royale National Park (Michigan, USA) is a remote island in Lake Superior that, until relatively recently, was void of earthworms. Its two native natricine snakes are known to feed on earthworms on the mainland; here, we confirm that eastern gartersnakes (Thamnophis sirtalis) are also feeding on earthworms on Isle Royale. It is unknown how this new important dietary source will impact the snake ecology on Isle Royale.
diet, eastern gartersnake, Isle Royale National Park, redbelly snake, Storeria occipitomaculata
Insular organisms have evolved in isolation from conspecifics on the mainland and in sympatry with other species native to that island. Islands are excellent models for more complex ecosystems and allow for a better understanding of predator-prey relationships because of the comparative reduction in species richness (
Many islands around the world have evolved interesting snakes with unique life histories (e.g.,
Earthworms can have extensive negative impacts in forested environments. They may remove the surface plant litter rapidly, alter the understory vegetation, and disrupt soil physiology (
It can be difficult to identify an earthworm as a species unless you are able to count the segments between the start of the worm and the clitellum (band), measure the total length of the worm as well as the length from the start of the worm to the clitellum (band), and also examine a picture of the underside of the worm; however, all are introduced species in the Upper Midwest. For example, Minnesota, United States, has at least 15 introduced species of earthworms. Ontario, Canada, has at least 15 confirmed invasive species (
Even though earthworms are now widespread in the Upper Midwest and several snakes are known to feed on them, little work has been done to document this prey source. Here we confirm that snakes isolated on an island are utilizing earthworms as prey and establish baseline data for the study of this over the next few years.
Isle Royale National Park, Keweenaw County, Michigan, United States (47.9763°N, 88.9313°W), is a relatively remote island in western Lake Superior. It is located 29 km from the Minnesota shore, 90 km from the Michigan shore, and 24 km from the Ontario, Canada, shore. Isle Royale was designated a National Park in 1940, and to this day, 99% of it is federally protected wilderness (
Isle Royale has two native species of snakes: Thamnophis sirtalis (Linnaeus, 1758), popularly known as the eastern gartersnake, and Storeria occipitomaculata (Storer, 1839), popularly known as the northern redbelly snake. It is unclear how they came to the island, though both are well-established and widespread; neither is well-studied in this environment. Thamnophis sirtalis is most notable on Isle Royale for its highly variable color morphs (
The following observation was made while visiting Isle Royale National Park: The snake was not captured or handled, and digital documentation of the event was taken.
On 23 June 2023, at 14:54 h, at the South Lake Descor Campground (47.969099, -80.975028), a small (presumably a 2022 neonate) Thamnophis sirtalis was found feeding on an earthworm (Fig.
There is a single record of an eastern gartersnake (Thamnophis sirtalis) consuming a Lumbricus terrestris Linnaeus, 1758 in what was previously the Ransom settlement, located on the northwestern side of the island near the present-day Daily Farm campground (
Earthworms, not native to the Upper Midwest of the United States, were presumably introduced to Isle Royale National Park in Lake Superior as byproducts of fishing in the area. At this time, we do not know how the introduction of earthworms and their expansion of range are going to impact the two native species of snakes on Isle Royale. It has been shown in other systems that the introduction of an abundant prey source can lead to increases in body size and thus increased reproductive potential in another natricine snake (
The presence and impacts of earthworms on the nearby Boundary Waters Canoe Area Wilderness on the border of Minnesota, United States, and Ontario, Canada, are well documented (
As stated by
JMR thanks the Grand Portage National Monument in partnership with the Grand Portage Band of Lake Superior Chippewa and the 1854 Treaty Authority. JK thanks his wife, Shri Karafa, who patiently waited for him to take pictures during their adventures.