Head to head
Hellbender vs Mudpuppy
Anglers in the eastern United States pull up both of these big aquatic salamanders and often cannot tell them apart, then wrongly assume both are venomous. The hellbender is the giant, up to 74 centimetres, with a flat head, loose frilly folds of skin along its sides, and no external gills as an adult. The mudpuppy is smaller, up to about 33 centimetres, and keeps a pair of bushy maroon external gills its entire life. They also want very different water.
| Hellbender | Mudpuppy | |
|---|---|---|
| Scientific name | Cryptobranchus alleganiensis | Necturus maculosus |
| Adult length | 30 to 74 cm; the largest salamander in North America | 20 to 33 cm |
| External gills | None as an adult; breathes through skin folds | Large bushy red gills kept for life |
| Water it needs | Cold, fast, clean, oxygen-rich streams and rivers | Tolerates warm, murky, slow, or still water |
| Body | Very flat head and body; wrinkled side folds | Rounder body; four toes on each foot |
| Activity | Hides under large flat rocks by day | Active year-round, including under winter ice |
| Role as indicator | Strong sign of a healthy, unpolluted river | Present across a wide range of water quality |
| Conservation status | Near Threatened; several populations declining sharply | Least Concern |
Hellbender vs Mudpuppy: common questions
Is a hellbender or a mudpuppy venomous or poisonous?
Neither. This is one of the most persistent freshwater myths in the eastern United States. Both are completely harmless salamanders with no venom and no dangerous skin toxin, and neither has teeth that pose any threat beyond a hard nip if you grab one. The fear comes from their size, their slimy skin, and their sudden appearance on a fishing line, plus a folk belief that they poison the water or ruin the fishing. In fact a hellbender in the river is a sign the water is clean, and both animals should be unhooked gently and released.
How do I tell them apart at a glance?
Look for external gills and look at the size. A mudpuppy has a conspicuous pair of dark red, feathery gills sticking out on each side of the neck, like tiny bottle brushes, and it is rarely longer than a ruler. An adult hellbender has no visible gills at all, has a distinctly flattened, spade-shaped head, loose wavy folds of skin running along its lower sides, and can be as long as your forearm and then some. If it is huge and has wrinkly skin flaps and no gills, it is a hellbender; if it is medium-sized with obvious frilly gills, it is a mudpuppy.
Why does the mudpuppy keep its gills but the hellbender loses them?
The mudpuppy is permanently larval, a condition called paedomorphosis: it becomes sexually mature while keeping juvenile features, including external gills, and never goes through a full metamorphosis. That lets it exploit water too poor in oxygen or too unstable for many amphibians. The hellbender does metamorphose, losing its larval gills at around a year and a half old, but instead of moving onto land it stays aquatic and switches to breathing through the enormously increased surface area of its skin folds. That method delivers plenty of oxygen, but only if the water is cold and fast enough to stay saturated, which ties the hellbender to pristine rivers.