The Reality of Blue Spiders
Blue coloration is rare in the animal kingdom, leading many to wonder if blue spiders truly exist. While uncommon, this unique hue does appear in some spider species. Despite common misconceptions, several spider species exhibit striking blue coloration. The presence of blue in spiders challenges the general perception that such vivid shades are almost exclusive to birds or fish. Its occurrence in spiders is a testament to the diverse ways nature produces color, highlighting the intricate adaptations and visual diversity found within the arachnid class.
Notable Blue Spider Species
The Gooty sapphire ornamental tarantula (Poecilotheria metallica) is a striking example of a blue spider. Native to a small region in central southern India, this arboreal species displays a brilliant metallic blue body with distinct yellow leg stripes. It typically inhabits holes in tall trees within deciduous forests, constructing asymmetric funnel webs. The Gooty sapphire is critically endangered due to habitat loss.
Another well-known blue spider is the cobalt blue tarantula (Cyriopagopus lividus). This medium-sized tarantula, with a leg span of around 13 cm, is native to tropical rainforests in Myanmar and Thailand. It is characterized by iridescent blue legs and a light gray body, with its blue coloration most evident under direct light. As a fossorial species, it spends most of its life in deep burrows it constructs in the ground.
Beyond tarantulas, some peacock spiders from Australia (Maratus genus) also showcase vivid blue patterns. Species like Maratus splendens and Maratus nigromaculatus incorporate bright blue into their elaborate courtship displays. These tiny jumping spiders use colorful abdominal flaps, covered in microscopic scales, to attract mates. Their blue is often part of a broader palette of colors.
How Spiders Get Their Blue Hue
Blue coloration in spiders results almost exclusively from structural color, rather than pigments. Unlike pigmentary colors, which use chemical compounds to absorb and reflect light, structural colors arise from light’s physical interaction with microscopic structures. These structures are typically found on the spider’s exoskeleton or specialized hairs and scales.
In many blue spiders, including tarantulas, the blue appearance comes from intricately arranged nanostructures within their modified setae or hairs. These structures, often lamellated walls or multilayered chitinous layers, are precisely spaced to interfere with specific light wavelengths. When white light strikes these structures, certain wavelengths are scattered or reflected, while others are canceled out, creating the perception of blue.
Peacock spiders achieve their blue through complex photonic systems involving chitinous layers with ridges and filaments. These arrangements create natural diffraction gratings or multilayer reflectors. The precise dimensions and arrangement of these nanostructures determine the exact shade and intensity of blue. While structural colors often produce iridescence, some spiders possess structures that reduce this effect, allowing for a more consistent blue display.