Michigan is home to over 500 different spider species. The question of which species holds the title of “biggest” is a common search query, often driven by the desire for accurate identification and information about their nature. Finding the true answer requires looking past exaggerated sightings and focusing on the species that consistently achieves the largest adult size within the state’s borders.
Identifying Michigan’s Largest Spider
The largest spider by leg span found in Michigan is the Dark Fishing Spider (Dolomedes tenebrosus). This species is often referred to as a nursery web spider or fishing spider. A full-grown female can achieve a total leg span reaching three to four inches, which is approximately the size of a person’s palm. The body itself, excluding the legs, typically measures between 0.6 and 1.0 inches long in females, while males are significantly smaller.
These spiders are generally pale to dark brown, and their abdomen is often marked with a series of chevron-like or “W”-shaped markings that can be distinct or broken. The legs are notably banded with alternating light and dark rings, adding to their robust appearance.
Distinguishing Features and Habitat
Despite its common name, the Dark Fishing Spider is highly adaptable and is not always found near water, though it is a powerful semi-aquatic hunter. While other species in its genus are closely tied to aquatic environments, Dolomedes tenebrosus thrives in wooded areas and forests. They can be found on tree trunks, under logs, or in leaf litter, often far from any pond or stream.
This spider is an active hunter that does not build a web to capture prey. It employs a sit-and-wait strategy, using its speed and size to ambush various insects and other arthropods. Although they are capable of running across water, diving beneath the surface, or even catching small fish, they more commonly hunt terrestrial prey. Their tendency to wander in search of food and shelter is why they frequently enter homes, particularly basements and garages in wooded locations.
Are Michigan’s Large Spiders Dangerous?
The large size of species like the Dark Fishing Spider often leads to the belief that they are dangerous, but size does not correlate with medical significance. The Dark Fishing Spider and other large species, such as Wolf Spiders (Lycosidae) and Giant House Spiders (Eratigena atrica), are not considered a threat to human health. They are shy, typically flee, and will only bite defensively if they are handled or accidentally pressed against skin. The vast majority of large spiders encountered in the state, despite their impressive appearance, are harmless predators that play an important role in controlling insect populations.
There are only two spider species in Michigan considered medically significant: the Northern Black Widow (Latrodectus variolus) and, rarely, the Brown Recluse (Loxosceles reclusa).
Northern Black Widow
The Northern Black Widow is identified by the female’s glossy black body and the distinct red hourglass marking on the underside of its abdomen. Its venom affects the nervous system. Bites are rare and usually only occur when a spider is guarding an egg sac or disturbed in its hiding spot.
Brown Recluse
The Brown Recluse is not native to Michigan, and confirmed sightings are extremely rare, making it highly unlikely for residents to encounter one. This spider possesses a venom that can cause localized tissue damage, but it is a reclusive species that prefers dark, undisturbed areas. Many suspected recluse bites are actually caused by other common spiders or medical conditions.