The Regal Jumping Spider, Phidippus regius, is one of the largest and most frequently encountered jumping spiders in North America. This charismatic arachnid is native to the southeastern United States and the Caribbean. Because of its relatively large size, people are often curious about just how big it can grow. Understanding the maximum size requires looking at the specific biological measurement used by researchers, which provides a definitive answer.
Defining Maximum Body Length
The standard measurement for determining a spider’s size is the body length, the distance from the front of the cephalothorax to the rear tip of the abdomen. This metric excludes the legs, offering a consistent and reliable figure across all specimens. The maximum size of Phidippus regius is a feature of the adult females, who typically attain a body length ranging from 15 to 22 millimeters (approximately 5/8 to 7/8 of an inch). Adult males are consistently smaller than the females, reaching a maximum body length of about 18 millimeters (roughly 3/4 of an inch). The overall size of the species can vary slightly depending on its geographical origin, with some regional populations exhibiting specimens that push the upper bounds of the established size range.
Sexual Dimorphism in Size
The size difference between the sexes, known as sexual dimorphism, is pronounced in the regal jumping spider. Females are not only longer than males but are also noticeably bulkier, possessing a larger and more rounded abdomen. This size disparity is biologically significant, as the female’s larger body is necessary for producing and carrying egg sacs.
Mature males typically present a sleek, darker appearance. Males are almost always black with distinct white markings on the abdomen, and they feature iridescent green-blue chelicerae.
In contrast, females exhibit a much wider variety of colors. Female coloration can range from shades of gray or tan to vibrant oranges and peaches, often with a colorful iridescent sheen on their chelicerae that can be pink, purple, or even green. This difference in coloration and overall robustness makes the female appear substantially larger than the male, even when their body lengths are close.
Leg Span Versus Body Length
Public perception of a spider’s size often relies on the visual length created by its legs, leading to confusion between body length and leg span. Leg span is measured from the tip of the first leg on one side to the tip of the fourth leg on the opposite side, representing the total area the spider covers.
While this measurement can make the Phidippus regius appear much larger, it is an inconsistent metric for size comparison. Body length remains the scientific standard because leg length can be highly variable and is not directly related to the spider’s mass or maturity. For instance, some larger male regal jumping spiders have disproportionately longer front legs compared to smaller males. This variation means that two spiders with the same body length might have very different leg spans.
Leg span is a more practical measurement for determining the size of a suitable enclosure, as it accounts for the space the spider needs to move. However, when answering the question of how big the species gets, the maximum body length of the adult female is the accurate and definitive metric to use.