Although not the loudest animal in terms of sheer decibels, the 0.07-inch (2-millimeter) water boatman species Micronecta scholtzi, pictured, does make the loudest sounds relative to its body size, scientists announced in June in the journal PLoS ONE.
Engineers and evolutionary biologists in Scotland and France recorded the boatman—which is roughly the size of a grain of rice—"singing" in a tank. The aquatic insect's songs peaked at 105 decibels, roughly equivalent to the volume of a pounding jackhammer within arm's reach.
The chirps are loud enough that humans can hear the sounds while standing at the edge of a boatman's pond. Fortunately for nature lovers, though, nearly all the sound is lost when the noises cross from water to air.
Remarkably, the boatman creates his songs by rubbing his penis against his belly, in a process similar to how crickets chirp. Sound-producing genitalia are relatively rare within the animal kingdom, but animals have evolved hundreds of other ways to boost their hoots, howls, and snaps.
Photograph courtesy Jerome Sueur, MNHN
Heck of a Howl
The howler monkey is the loudest land animal. Its calls, which some say are actually more like growls, can be heard up to three miles (five kilometers) away. (Watch a howler monkey video.)
The monkey's volume comes from its enlarged hyoid bone, a U-shaped bone in the howler's throat that "isn't actually hooked to any of the [other] bones, so it kind of just hangs there," said Dell Guglielmo, caretaker for two howler monkeys at the National Zoo in Washington, D.C. The enlarged bone creates a throat sac in which the monkey's calls resonate before booming out.
The monkeys have a variety of calls, likely for communicating location, protecting territory, and guarding mates, but their vocabulary is yet unknown to humans.
Photograph by Joel Sartore, National Geographic
Loud as a Lawnmower
Only the males of the common coqui frog sing, but their calls, recorded at peaks of a hundred decibels from three feet (a meter) away, make them the loudest known amphibians.
The nocturnal frog's two-part "co-qui" call has a two-part meaning: Other male frogs respond to the territorial "co" part of the call, while females are attracted to the "qui."
In the coqui's native habitat of Puerto Rico, the frogs are considered part of the island's natural heritage. But in Hawaii, where the frogs are quickly establishing themselves as an invasive species, residents have spent many sleepless nights due to the noisy frogs, which, in aggregate, are comparable to a lawnmower running all night, according to the Hawaii Department of Agriculture.
Photograph by Fran Hall, National Geographic
The blue whale is the loudest mammal of them all, with vocalizations that reach 188 decibels.
Blue whales don't have songs as complex as those of humpback whales, but their low-frequency "pulses"— some below the range of human hearing—have been recorded more than 500 miles (805 kilometers) away.
A few years ago researchers found that the whales had been lowering the frequencies of their songs even more—by up to 30 percent since the 1960s in some populations. One theory suggests that the whales no longer need to sing at "high" pitches to be heard at a distance, because the species, while still endangered, has rebounded since whale hunting was banned in 1966.
Photograph by Flip Nicklin, National Geographic
Snap of Doom
The snapping shrimp doesn't sing, chirp, wail, or hoot, but it just might be responsible for the loudest noise produced by any living being.
In colonies, the shrimps' noise is enough to hide submarines from sonar.
Photograph from WaterFrame/Alamy
You wouldn't want to be around when oilbirds come home to roost—these cave dwellers, the loudest known birds, can be deafening when gathered in large groups.
Oilbirds use echolocation to navigate in completely dark caves. But, unlike the calls of most bats, the birdcalls are within the range of human hearing. Each bird can produce squawks and clicks up to a hundred decibels at close range, and colonies can contain thousands of birds.
The oilbirds appear to use echolocation only within their cave homes and not during their nocturnal foraging. This could be because their sensitivity isn't very high: In one experiment, oilbirds flew straight into plastic discs that were 4 inches (10 centimeters) wide, but they were able to avoid 8-inch (20-centimeter) disks and larger.
The mole cricket species Gryllotalpa vinae is the loudest of the insects. The critter uses its specialized front legs to dig a megaphone-shaped burrow. Standing inside that dugout, a cricket can chirp loudly enough that humans can hear it nearly 2,000 feet (600 meters) away.
Microphones placed three feet (a meter) from a cricket's burrow entrance have recorded peak sound levels of 92 decibels, or about the volume of a lawn mower.
In fact, using the burrow, G. vinae is able to turn an astonishing 30 percent of its energy into sound.