SCIENCE news this year has been dominated by Covid-19. Research has happened at an incredible speed, with scientists working around the clock to make rapid progress.

At the start of the year, we didn’t know that Sars-CoV-2 existed. Just nine months later, humanity has collectively sequenced and analysed its genome in detail, found evidence for a range of effective treatments and started the development of hundreds of candidate vaccines.

Other areas of science might seem sluggish by comparison. Indeed, science normally feels like it progresses at a snail’s pace. However, there is always more than meets the eye to nature. Snails are no exception.

The sea is full of snails. Billions of them live in the top layers of the ocean. Most are small: from a few millimetres to about a centimetre in size.

Despite their tiny size, they collectively have large effects. For example, their shells are made of calcium carbonate.

These shells play an important role in the carbon cycle and ocean acidification. More than 10 per cent of the global carbonate flux occurs when sea snails die and their shells sink to the bottom of the sea where they dissolve.

Such snails feed in the surface waters of the ocean, which contain the highest density of food. Feeding takes place at night to reduce the risk of being eaten by predators.

As night turns to day, these snails return from the surface waters to the depths several hundred metres below. For most of human history, this daily migration has gone completely unnoticed.

Scientists have categorised the diverse species of sea snails. They come in many shapes and sizes. Some have coiled shells; some have round. Some, called “sea butterflies,” have “wings” which they flap to swim around.

In recent decades, researchers have looked at the distribution of different species of sea snails. However, it’s difficult to study how they swim because they have to be retrieved from the sea and transported back to laboratories.

Many cannot be cultured in an aquarium. So, until recently, the sea butterflies have kept their mysteries.

A group of researchers, including oceanographers and engineers, collected snails of different species in Bermuda at night. Most were “sea butterflies,” although the researchers also collected a so-called “sea angel” species which lacks a shell entirely.

They then took them back to the laboratory for study. They tracked their rising and falling in 3D in a small saltwater aquarium: a cube of 15cm, allowing up to 15 “full strokes” in a vertical length for even the largest snail.

Having the resulting trajectories of the snails allowed the researchers to analyse them in terms of fluid mechanics: the study of how fluids move.

They hypothesised that different shell shapes and sizes might have an effect on how the snails swam up to feed at night.

Indeed, the characteristic swimming pattern of the snails with wings was broadly similar, a zig-zagging “sawtooth” motion caused by the repeated flapping of their wings where the snails sink briefly in between each flap.

Some snails’ overall trajectory was essentially straight while others traced out a spiral path.

The larger snails both rose and sank at the greatest speeds. The researchers found that larger snails spent the day at greater depths in the wild.

There were also interesting differences between the snails. High-speed cameras allowed the researchers to slow down the “flapping” of the wings and examine it in detail.

The smaller the snail, the more viscous seawater feels for them. According to Dr David Murphy, one of the team at the University of South Florida, “Tiny snails with coiled shells swim more slowly, whereas larger snails with bottle-shaped or wing-shaped shells swim faster because their larger sizes allow them to overcome the effects of water viscosity.”

The researchers also found that the shape of the shell had a large impact on how the snails swam. Despite tiny snails with coiled shells being the slowest, larger snails with coiled shells had the fastest speeds with respect to their body size.

They could swim at high speeds of 45 body lengths per second — the equivalent for a two-meter-tall person would be 90 meters a second.

The researchers saw that snails with more spherical shells glided down at a consistent angle of 20° to the vertical. The shell acts as a hydrofoil, providing lift in water like a wing in air, and reducing their sinking rate.

The researchers described this as akin to “hang-gliding.” Previously, the same team has shown that sea butterflies fly through water just like insects fly through the air.

The similarities are not just superficial: studying the dynamic principles underlying the different organisms helps understand engineering problems. There is the long-term possibility of using the swimming styles of the snails to develop “bio-inspired” underwater vehicles.

The swimming trajectories the researchers found are beautiful in their own right, but knowing they are made daily by billions of snails, unseen, gives them an extra level of fascination. While we often think of space as the great unknown, there is still so much to discover on this planet.

The trajectories of these sea snails show the beauty and wonder that science can help us to see. While Covid-19 grabs the headlines, most science progresses at a snail’s pace: largely unobserved, but extraordinary if you pay attention.