When a Texas man complained of a discomfort in his nether regions, surgeons did not expect to find what had been burrowing underneath his skin.
Mark Johnstone of Bayou Vista checked himself into the emergency room after enduring days of excruciating pain in his testicles.
"He had two weird pimply things on his skin, and he was starting to ooze pus," parasite expert Dr. Dan Riskin told InsideEdition.com.
In addition, Johnstone could be seen in footage provided by Animal Planet doubling over periodically, in pain.
Despite being at a loss to what could have been causing the pain, doctors suspected there may have been something inside his scrotum. They proceeded to anesthetize the area and prepare for surgery.
They were then shocked to find a botfly larva hiding within the skin of his scrotum.
"It ended up being two of them," Dr. Riskin explained. "It's not until it gets to a significant size that you realize something is wrong."
According to Dr. Riskin, Johnstone and his partner Brenda had just been on a trip to Costa Rica over Thanksgiving.
As he was undressing in the woods, Johnstone got what appeared to be two mosquito bites on his scrotum, but thought nothing of it.
"He didn't even consider the possibility of a botfly," Dr. Riskin said.
Dr. Riskin explained botflies, a family of parasites who birth their young inside a mammal, often begin their process by laying eggs on a mosquito's belly.
When the mosquito feeds on a mammal, the parasite's eggs enter the skin through the wound of the mosquito bite.
"You have no idea it's there for days and days," Dr. Riskin explained. "You have a mosquito bite on your arm, and then it starts getting bigger, and then it starts to hurt."
The wound from the bite also expands, which is where the growing maggot might surface for air. "It's the grossest thing you can imagine," Dr. Riskin said.
Luckily, Johnstone caught the bug in the nick of time.
Doctors were able to remove the parasite seamlessly, and Dr. Riskin, who once had a botfly burrow inside his head, said the healing process is quick.
"You might be sore for a couple of days, but once it's out, it's out," Dr. Riskin explained. "There's a lot of nerves along the genitlia, so he probably suffered more than other people."
Despite the pain Johnstone experienced, Dr. Riskin explained the botfly is one of the least harmful parasites to exist.
"I think it drives home the point of the show — that parasites have better imaginations of how to make your life more terrifying than you could possibly come up with on your own," Dr. Riskin said.
An all-new episode of Monsters Inside Me premieres tonight at 10/9c on Animal Planet.