To better gauge the trade-offs between shell size and defensibility, Laidre collaborated with an engineer to create the hermit crab eviction machine, a device that holds onto an occupied shell and measures how much force it takes a scientist to pull the crab out (crabs are not harmed or left homeless). It's essentially a portable load cell that can survive the sun, sand, and humidity of the field.

The force required to evict a hermit crab is an important measurement, because hanging on to their homes is a matter of life and death for crabs. "If you are evicted, there's a real strong probability that what is left at the end of one of those chains is something that's too small for you to even enter," Laidre says. In his field area on a beach in Costa Rica, a homeless crab can quickly succumb to predators or heat: "You're really dead meat in a sense."

Studying the minds of other animals comes with a challenge that human psychologists don't usually face: Your subjects can't tell you what they're thinking. To get answers from animals, scientists need to come up with creative experiments to learn why they behave the way they do. Sometimes this requires designing and building experimental equipment from scratch.

The DIY contraptions that animal behavior scientists create range from ingeniously simple to incredibly complex. All of them are tailored to help answer questions about the lives and minds of specific species, from insects to elephants. Do honeybees need a good night's sleep? What do jumping spiders find sexy? Do falcons like puzzles? For queries like these, off-the-shelf gear simply won't do.

The eviction machine was inspired by Laidre's curiosity about crabs. But sometimes new questions about animals are inspired by an intriguing device or technology, as was the case with another of Laidre's inventions: the hermit crab escape room (more on that below). The key, Laidre says, is to be sure the question you're asking is relevant to the animals' lives.

Here are five more contraptions custom-built by scientists to help them understand the lives and minds of the animals they study.

The brainy birds in the parrot and crow families are the stars of scientific studies on avian intelligence. Now these smarties have a surprising new rival: a falcon. Raptors are not known for creative problem-solving, but behavioral ecologist Katie Harrington of the University of Veterinary Medicine Vienna suspected the striated caracara falcons she had observed on a remote Falkland Island were different. "They're really interested in investigating things," she says. "They're very intelligent birds in general."

To test their smarts, Harrington took inspiration from an "innovation arena" (left), designed for Goffin's cockatoos, which are members of the parrot family known for their problem-solving abilities. It's a semicircular array of 20 clear plastic boxes containing puzzles requiring different solutions to release rewards like cashews or corn kernels. Hauling the seven-foot-wide arena to the Falklands was not an option. So Harrington designed a 16-inch-wide "innovation box" attached to a wooden board, with eight compartments and puzzles adapted from the cockatoo studies.

The birds loved it. "We were having caracaras run full speed to participate," Harrington says. The challenge was keeping other birds away while one worked the box. The birds were able to solve the puzzles, which involved things like rattling a plank to knock down a bit of mutton or pulling a twig out from under a platform with mutton on it. They were even able to solve a tricky one that required them to punch a hole in a piece of tissue that obscured the treat -- a task that eluded some cockatoos.