Reptiles
Painted Turtle
Chrysemys picta · also called painted turtle, mud turtle
The painted turtle is the little dark turtle basking in a row on a half-sunk log at almost any North American pond, its shell edged with red and its neck striped in yellow. It is the most widespread native turtle on the continent — and one of the toughest, with hatchlings that can freeze in the nest and adults that can spend months underwater without breathing.
Overview
Painted turtles live in slow, shallow, soft-bottomed fresh water — ponds, marshes, ditches, lake edges — across most of North America, from Nova Scotia to British Columbia and south to Louisiana. They are omnivores (more carnivorous when young, more herbivorous as adults) and dedicated baskers, hauling out on logs and banks for hours to warm up and control parasites and algae.
Frozen hatchlings
Painted turtle hatchlings stay in the underground nest through their first winter, and in the north the nest can freeze. They survive by supercooling or by tolerating ice in their tissues down to about -4 °C, loading their cells with glucose as protection, then thawing in spring. Adults cannot do this — it is a hatchling-only trick.
Winters under the ice
An adult spends winter buried in pond mud, metabolism near zero, absorbing trace oxygen through the mouth lining and cloaca. If the water runs out of oxygen entirely, it switches to anaerobic metabolism, buffering the acid with minerals from its own shell, and can last months with no oxygen — among the most extreme anoxia tolerance of any air-breathing vertebrate.
Temperature and sex
Warm nests produce females, cool nests males — a hot summer can skew a whole cohort.
Status
The painted turtle is Least Concern and abundant, thriving in human-made ponds and ditches, though local populations suffer from road deaths of nesting females, wetland loss, and heavy nest predation by raccoons and skunks.
Painted Turtle: common questions
How can a baby painted turtle survive being frozen?
Painted turtle hatchlings typically emerge from the egg in late summer but do not dig out of the nest; instead they stay in the underground chamber, a few centimetres deep, through their first winter, and emerge the following spring. In the northern part of the range, the nest can freeze. The hatchlings deal with this in two ways depending on conditions — they can supercool, staying liquid below freezing as long as no ice touches them, or, if ice does form, they can tolerate a substantial fraction of their body water turning to ice and their core temperature dropping to around -4°C, then thaw and revive. They achieve this partly by loading their tissues with glucose and other protective solutes. Adult painted turtles cannot do this and would die if frozen; it is specifically a hatchling adaptation.
How do adults breathe under the ice all winter?
They mostly don't — they drastically reduce their need for oxygen. An adult painted turtle spends the winter buried in the mud at the bottom of a pond, its body temperature just above freezing and its metabolism slowed to a tiny fraction of normal. At that rate, the small amount of oxygen it can absorb directly from the water through thin-skinned areas — the lining of the mouth and throat and, notably, the cloaca ("cloacal respiration," sometimes called breathing through the butt) — is enough to keep essential processes going for a while. If the water becomes completely oxygen-free, the turtle switches to anaerobic metabolism, buffering the resulting acid with minerals released from its own shell and skeleton, and can survive months without any oxygen at all — one of the most extreme anoxia tolerances of any air-breathing vertebrate.
Why is the painted turtle so common when other turtles are declining?
It is a generalist that does well in exactly the habitats people create and leave behind. It uses almost any shallow, slow, soft-bottomed fresh water — including farm ponds, drainage ditches, borrow pits, and urban stormwater ponds — it eats a wide range of plant and animal food, it tolerates some pollution, and it basks readily on any available log or bank. It also has the largest geographic range of any North American turtle. That said, "common overall" hides local problems — road mortality of nesting females, loss of small wetlands, nest predation by inflated populations of raccoons and skunks, and collection can all reduce or wipe out local populations, and some western and southern subspecies are of conservation concern.
How do you tell a painted turtle from a red-eared slider?
They overlap in range (partly because sliders have been released widely outside their native area) and both are small, dark, basking pond turtles with yellow and red markings, so they are often confused. The painted turtle has a smooth, flat, unkeeled shell and bright red bars or crescents around the shell's outer edge (the marginal scutes), and its head stripes are yellow with no large red patch. The red-eared slider has a slightly domed, faintly textured shell, a distinctive broad red stripe or "ear" patch behind each eye, and it grows larger. Old male sliders often turn very dark and lose their markings, which adds to the confusion.