To celebrate Valentine’s Day, I took a tour of the Maryland Zoo with zookeeper Danielle Regan, who manages the Maryland wilderness area and holds a dizzying breadth of knowledge about animal sex. Here are some highlights to make you rethink how humans celebrate love.


Charles Darwin once wrote that there “is grandeur in this view of life” to think that evolution has produced innumerable beautiful creations on this Earth. One of those creations? The squirrel’s shovel-penis.

Squirrels are one of many mammals that have a bone — called a baculum — in their phallus. Its purpose? To dig out semen plugs.

“If you’re a male squirrel, when you’re done having sex with the female, you will plug her vagina with a mixture of fluids that hopefully stop another male from breeding with her,” Regan said. “But, of course, squirrels have evolved this shovel-shaped baculum to remove those plugs.” During post-sex self-care, females sometimes remove the plugs on their own, too, a rather neutral position in the plug vs. shovel arms race.

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Does size matter?

Which animal do you think has the smallest phallus-to-body ratio? You may be surprised it’s the gorilla. While a male silverback can weigh twice as much as a human adult, their penises are barely over 1 inch long. The culprit: long-term relationships, Regan said.

“If you’re a gorilla, you’re definitely not a promiscuous species,” Regan said. That preference for stable, long-term relationships between one male and multiple females makes phallus size less important for females than the male’s strength, protective nature and an ability to secure food, she said. There’s less of a need to show off.

If size is important to you, then look no farther than the barnacle. These coastal kings have a phallus eight times bigger than their bodies — the biggest in the animal kingdom. Bachelors in calm waters have longer and softer phalluses, while those braving the rough, choppy seas have shorter, more rigid phalluses. In harsh conditions, “you don’t want a phallus that’s loosey-goosey,” said Regan. “You want to be able to find a partner.”

Barnacles are also hermaphrodites that constantly copulate with their neighbors. “Everyone’s in each others’ pot,” Regan said.

Stop and start

North American river otters take some time to get things going. They are induced ovulators, which means they only ovulate after having sex, rather than having regular cycles like humans, Regan said. It is the second act of sex, after they begin ovulating, that allows them to become pregnant.

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The otters also have delayed implantation. “The embryo will grow for a couple of months, and then stop completely and lay in stasis for months,” she said. Months later, the embryo will start to develop again, which allows the mother to coincide the timing of her pup’s birth with the warmest time of year. “I have no idea how any animal evolved such an insane way of stopping an embryo and then starting it right back up again months and months later, but it is certainly interesting and advantageous for cooler aquatic mammals,” she said.

The turtle’s secret

“Male turtles have larger tails than female turtles,” Regan said. “That’s to help their large, terrifying phallus have space to come out.”

A turtle’s penis has a certain horrific quality to it. Regan described them as a flat lion’s mane mushroom, sometimes more bulbous or disc-shaped depending on the species. They’re also very sensitive and kept hidden within the male’s shell.

High quality images are hard to come by, but you can see a video here and picture here at your own peril.

The mysterious clitoris

The clitoris can take on wildly different shapes and sizes between animals. In dolphins, the s-shaped organ is encouraging scientists to explore how some animals might have sex just for pleasure.

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Meanwhile, hyena clitorises are hard to miss. Around seven inches long and called a pseudo-penis, it is near indistinguishable from the male penis — fitting for a matriarchal species that values the alpha female. Unfortunately for the females, they also give birth through it.

It was only a couple months ago that scientists published research to support their discovery that snakes have two clitorises. Although there is plenty of room for jokes about “finding the clitoris,” which Regan has no qualms with, she also used the moment to speak on the role women play in science.

“Of course it was a woman who discovered this,” she said, as male scientists may not necessarily be looking for those anatomical features in animals. “I wanted to use this as an example to encourage women to pursue science,” given how their unique perspectives can lead to research that changes the field.

A takeaway message from Regan? Go find new clitorises, future scientists.

Want to learn more? The Maryland Zoo is holding Galentine’s Flamingle Brunch on Sunday, hosted by Regan.

Krishna Sharma is an audience engagement editor for the Baltimore Banner. You can find him on the Banner's TikTok and Instagram. He has a background in environmental journalism and ecology. Do you have any tips or feedback? DM or email me!

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