How many endangered animals can fit into your carry-on luggage?

Titi monkeys. Click image to expand.
Titi monkeys

A smuggler was stopped at the Mexico City airport on Friday carrying 18 titi monkeys in a girdle. The Mexican citizen, who had purchased the endangered animals for $30 each in Peru, carried them on his body because he was afraid the security X-ray used on luggage would damage the tiny primates. How many titi monkeys could he have stuffed into a carry-on?

Around 28 adults. The carry-on luggage limit is typically 22 by 14 by 9 inches, while Titi monkeys range from 11 to 17 inches in length and run about 4 inches across and 2 inches thick. Smaller species of titi monkeys could be stacked two high, two across, and seven deep. (Their tails, which are as long as their bodies, would have to be moved into the empty spaces between them.) That many monkeys would push the carry-on weight limit, though. Titis weigh 2 pounds each, and airlines often have a 40-pound cap.

Of course, transporting primates in this way would be both cruel and ineffective, since many or all of the animals could die. (Two of the titis involved in the Mexico City incident perished. And girdles are probably more life-sustaining than overhead bins. Whether or not you hold a license to transport endangered species, stuffing titis into a bag by the fistful would also, of course, be illegal, as there are strict rules governing primate transportation. According to U.S. law, a carrying container must provide enough space for the animal to turn around freely and sit upright without touching the ceiling, and at least 8 percent of the walls must be open for ventilation. (A roll-aboard that satisfied these requirements would be rare indeed.) Plus, you can only legally transport one primate per container. Two may travel together only if they are a bonded male-female couple, a mother and her nursing infant, or a compatible pair of prepubescent juveniles. (Titis hit puberty at around 18 months.)

Research has shown that any transport, legal or otherwise, stresses monkeys. During a flight, monkeys obsessively hug themselves—a sign of anxiety in nonhuman primates. And the stress may extend beyond the move. Relocated monkeys spend less time engaging in positive social behaviors such as reciprocal grooming.

Bonus Explainer: Law, ethics, and safety notwithstanding, how many endangered animals could fit into a suitcase? More than 100 million, if you could find that many Mesonerilla prospera, a critically endangered invertebrate that lives in the mud in Bermudan caves. At just 0.078 inches in length and 0.02 inches across, they are among the smallest known endangered animals.

If you want to stick with endangered vertebrates, you could try the Paedocypris progenetica: At less than one-third of an inch long, it’s the world’s smallest fish. While you might be able to fit more than 600,000 of them in your standard carry-on, filling your bag with the peat that sustains them would put you way over your weight limit. A suitcase full of wet peat, which is slightly denser than water, would tip the scales at 112 pounds.

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