Many people wonder about insects with six legs that resemble spiders, often due to a misunderstanding of arthropod classification. While spiders typically possess eight legs and belong to the class Arachnida, insects are characterized by their six legs and membership in the class Insecta. Some creatures, however, blur these lines with their appearance, leading to frequent misidentification. This article will clarify which animals might fit this description and explain the biological differences that set them apart.
Identifying the Mystery Creature
The creature most commonly mistaken for a six-legged spider is the harvestman, also known as a “daddy longlegs.” Harvestmen are arachnids, distinct from both insects and true spiders. Their long, thin legs and small, oval body often cause confusion. Though they have eight legs like other arachnids, two are often held forward as sensory organs, giving the impression of fewer walking legs. This allows them to navigate their environment.
Harvestmen typically have bodies ranging from 3.5 to 9 millimeters in length, though their legs can be many times longer, sometimes exceeding 15 centimeters. Unlike spiders, they do not produce silk or build webs.
Harvestmen lack venom glands, unlike spiders, and use chelicerae (jaws) to tear food. They are omnivores, feeding on soft-bodied insects, dead animals, and even plant matter and fungi. When threatened, some species release a foul-smelling fluid or detach a leg to distract predators.
Understanding Arachnids and Insects
Understanding the biological differences between arachnids and insects is key to categorizing these creatures. Both are part of the phylum Arthropoda, meaning they have exoskeletons and jointed legs. Insects (class Insecta) are defined by having three distinct body segments: a head, a thorax, and an abdomen. They possess six legs, typically have antennae, and many species have wings.
Arachnids (class Arachnida), including spiders, scorpions, mites, and harvestmen, generally have two main body segments: a fused cephalothorax (head and thorax) and an abdomen. Most adult arachnids have eight legs, lack antennae, and do not have wings. Harvestmen are unique among arachnids because their cephalothorax and abdomen are broadly fused, making their body appear as a single oval structure without the distinct “waist” seen in true spiders. Harvestmen typically have only two eyes, often on a raised turret.
Insects That Mimic Spiders
While harvestmen are arachnids, some true insects with six legs have evolved to visually resemble spiders through a phenomenon called Batesian mimicry. This adaptation helps them deter predators. For instance, certain types of jumping plant bugs have patterns on their bodies or wings that resemble spider eyes or legs. This mimicry is often effective from specific angles, making the insect appear as a spider to potential predators.
Some robber flies also exhibit mimicry, with certain species resembling venomous spider wasps. These flies, despite having only two wings and no stinger, display colors and behaviors, such as making stinging motions, that imitate their more dangerous models. Certain crickets, commonly known as “spider crickets” or “camel crickets,” are mistaken for spiders due to their long legs and humpbacked appearance. These crickets are wingless and jump long distances when startled, contributing to their spider-like perception.