Devil rays, which belong to the genus Mobula, are often confused with their close relatives, the true stingrays, leading to questions about their defensive capabilities. The answer is straightforward: Mobula rays do not possess the venomous, barbed spine characteristic of true stingrays. This misconception stems from the shared flattened body shape and the long, whip-like tails present in many ray species. Devil rays, including manta rays now classified within Mobula, are generally considered harmless to humans due to their gentle nature and filter-feeding diet.
The Absence of a Venomous Barb
The confusion about devil rays stinging is understandable, given the anatomical similarities across the larger group of cartilaginous fish known as batoids. The true stingray’s weapon is a highly specialized, defensive structure known as a caudal spine. This serrated barb is coated in venomous mucus, which is released when the spine punctures a target.
Devil rays lack this complex, venom-delivering system. The largest species, such as the giant oceanic manta ray and the reef manta ray, have long, slender tails that lack any spine or barb entirely. Some smaller Mobula species, like the spinetail devil ray, may possess a rudimentary stinger. This structure is significantly smaller, lacks a potent venom gland, and is often encased or non-functional, rendering it harmless.
The evolutionary trajectory of the Mobula genus explains this lack of a defensive barb. True stingrays belong to the family Dasyatidae and are benthic, meaning they live on the seafloor, often buried in the sand. Mobula rays, conversely, are pelagic, living in the open water column where they actively swim to strain plankton. Their primary defense is their size and speed, making a venomous spine a less necessary adaptation for their lifestyle.
Defining Mobula Rays and Their Kin
Taxonomic classification clarifies which rays pose a stinging threat. Devil rays belong to the family Mobulidae, the genus Mobula. These filter feeders are distinct from the Dasyatidae family (true stingrays) and the Myliobatidae family (venomous eagle rays).
Visual identification provides clear markers for distinguishing these groups. Mobula rays are characterized by their large, flattened, diamond-shaped bodies and the prominent, fleshy, horn-like cephalic fins that project forward from their heads. These fins are used to channel water and plankton into their mouths, which, in the case of manta rays, are positioned terminally at the front of the body. Devil rays, while similar in shape, typically have their mouths located on the underside of their body.
In contrast, true stingrays and eagle rays have a more disc-like or flattened body shape and lack the distinctive cephalic fins found on Mobula species. Eagle rays, such as the spotted eagle ray, are identifiable by their elongated snouts and the presence of one or more venomous barbs at the base of their whip-like tails.
Behavior and Interaction with Humans
Devil rays exhibit a placid temperament, consistent with their diet of plankton and small crustaceans. These animals are highly migratory, often traveling in large groups, and tend to avoid direct interaction with divers and boats. Their immense size, with wingspans up to 17 feet for some species, and their tendency to spend time near the surface make them vulnerable to human activities, but they are not aggressive.
The primary risk they pose to humans is purely accidental and related to their impressive breaching behavior. Devil rays are famous for leaping entirely out of the water, sometimes reaching heights of up to two meters before crashing back down with a large splash. The reasons for this behavior are not fully understood, though hypotheses include communication, courtship displays, or an effort to dislodge parasites. Instances have been recorded where a large, airborne ray has accidentally landed on a small boat or a person, causing significant injury due to the sheer force and weight of the animal.
Conservation efforts are focused on the Mobula genus, as these slow-reproducing species are vulnerable to overfishing. They are particularly targeted for their gill plates, which are used in some Asian health tonics. Their low fecundity, giving birth to only a single pup every two to three years, means their populations cannot sustain high catch levels.