The turtles you see basking in the sun in the Alewife Brook, along the Mystic River or at Fresh Pond are probably painted turtles (Chrysemys picta), the most widespread native turtle in North America. Another common one is the red-eared slider, but it is not native: Red-eared sliders used to be sold in pet shops in Massachusetts – they are now illegal to sell or own – and people released them into the wild, where they’ve been able in some places to outcompete our natives. The two look similar but you can tell the difference because the sliders have two red streaks on the sides of their heads; the painted do not have red streaks, and their shells are flatter.
Adult painted turtles spend winters in ponds under ice. Under water, they switch from taking in oxygen from the air to taking in oxygen from the water through blood vessels in their skin. Without oxygen in their lungs, they cannot stay afloat, so they sink to the bottom of the water. There is little or no oxygen in water at lower depths, so the turtles go into a dormant state. They can live for months without oxygen and without eating. When underwater and not breathing, turtles can pump blood throughout the body, avoiding the lungs. They can tolerate lower oxygen levels than other reptiles.
When we exercise, our bodies use oxygen to break down glucose for energy. During intense exercise, muscles are oxygen deprived, so our bodies make lactate instead. Lactate can be converted to energy without oxygen. This causes lactic acid to build up in the bloodstream, though, which can lead to muscle pain. The pain is temporary, and once we stop exercising, the liver and kidneys catch up and clear excess lactic acid from the body.
The same thing happens to painted turtles. They use oxygen to get energy from stored glucose. In the bottom of a pond without oxygen, they convert lactate to energy, leading to a buildup of lactic acid in the bloodstream. Lactic acid can be stored in the turtle’s shell without harming the shell, though. It is estimated that up to 45 percent of the lactic acid a turtle produces during dormancy is stored in the shell. The turtle’s shell and bones also release calcium and magnesium carbonates to neutralize lactic acid (analogous to taking Tums to relieve acid indigestion).
Another turtle feature that helps painted turtles survive months at the bottom of a pond without eating or breathing is that their metabolism slows down immensely. The metabolic rate of a dormant turtle is more than 10,000 times lower than that of a similarly sized mammal resting at normal body temperature. A dormant turtle’s heart usually beats once every two to three minutes, but it can go as long as five minutes between heartbeats.
Turtles have a top shell, called a carapace, made up of vertebrae and rib bones that have broadened and fused together. The stomach covering, called the plastron, is made of the breastbone and ribs that have calcified and fused together. The shells are covered in plates, called scutes, made of keratin, the material that fingernails and horns are made of.
Because turtles have rigid shells, their lungs cannot expand to breathe like we do. Instead muscles attached to organs help them breathe. The liver is connected to the right lung and the stomach is connected to the left lung. When stomach muscles contract, the organs are pulled away from the lungs, and the turtle inhales. When the muscles relax, the organs are pushed into the lungs, and the turtle exhales.
Painted turtles, like other reptiles, are cold-blooded and cannot regulate their body temperature. For this reason, you may spot them basking in the sun to warm up. At sunrise, painted turtles emerge from the water and bask for several hours until their body temperature reaches 63 degrees to 73 degrees Fahrenheit. Then they return to the water to forage for food. Once the turtle cools down, it returns to bask again. The turtle repeats this cycle two or three times during the day. At night, the turtle drops to the bottom of a pond or river, where it sleeps until daylight returns. Painted turtles spend up to six hours each day basking in the sun.
Painted turtles mate from March to mid-June. After mating, the female leaves the water to dig a nest on land. She lays five to six eggs some time from May to July, when conditions seem favorable. She covers the eggs with soil and leaves them. The eggs incubate for up to 80 days. The temperature of painted turtle eggs determines the sex of the baby turtles. In one study of northern painted turtles, during the middle third of incubation, when egg temperatures ranged from 86 degrees to 90 degrees Fahrenheit, the hatchlings were all female. When the egg temperatures ranged from 71 degrees to 79 degrees Fahrenheit, the hatchlings were all male. Intermediate or varied temperatures produced male and female turtles. Some scientists are concerned that climate change will change the ratio of male to female painted turtles, leading to reduced populations.
Baby painted turtles that are born late in the season may spend their first winter in their nests on land. If the temperature drops, the water in their bodies can freeze, yet they can still survive. (Adult painted turtles, on the other hand, cannot survive being frozen.) The baby turtles grow until they reach sexual maturity. This can be as little as two years for males but can be six to 16 years for a female. Painted turtles can live for 40 years in the wild.
Reader photo
Maren Clark spotted this snail near Tipping Cow Ice Cream in Somerville.
Have you taken photos of our urban wild things? Send your images to Cambridge Day and we may use them as part of a future feature. Include the photographer’s name and the general location where the photo was taken.
Jeanine Farley is an educational writer who has lived in the Boston area for more than 30 years. She enjoys taking photos of our urban wild things.
A stronger
Please consider making a financial contribution to maintain, expand and improve Cambridge Day.
We are now a 501(c)3 nonprofit and all donations are tax deductible.
Please consider a recurring contribution.