Want to see butterflies in your backyard? Try doing less yardwork

Making the world safer for butterflies can be as easy as doing a bit of nothing.

Letting some part of a yard go unmown can boost the number of butterflies and moths sighted there, says ecologist Richard Fox. That long-grass patch may be as elaborate as an all-native meadow dotted with flowers or as simple as some didn’t-mow corner by the back fence. Nectar-rich blooms that attract the fliers may pop up, but the biggest win comes when caterpillars don’t “get chopped in half every week by the lawn mower,” he says. “It’s not about having special grasses. It’s about resisting the urge to tidy everything.”

Enthusiasts have been no-mowing for years. There’s even a no-mow May trend aimed at giving pollinators safe havens. Yet Fox, of the nonprofit Butterfly Conservation based in East Lulworth, England, didn’t know of any scientific studies of how much butterflies might be using the refuges. So he and ecological statistician Lisbeth Hordley analyzed six years of citizen science data from their organization’s Great Butterfly Survey. They found records with enough data from about 600 yards scattered around England, Scotland and Wales.  

Neighborhood matters, their study concludes. In a yard surrounded with other houses, long grass could boost butterfly abundance as much as 18 percent, the statistical model built with the real butterfly data suggests. For yards surrounded entirely by farms, the increase could be as large as 93 percent, Hordley and Fox say in the June 15 Science of the Total Environment. Even if individual yards don’t have huge increases in butterfly abundance, the total area of safe space could add up if a lot of yards went a little wild.

While the surveys focused on butterflies, the practice could be even more beneficial for moths; their caterpillars are more likely than butterfly larvae to munch on grass. Moths, which far outnumber butterflies and tend to be night-flying, are a “key cog in the ecosystem,” Fox says. “They’re propping up food chains for many of our garden birds, many small mammals, bats of course.” 

Leaving a swath of yard unmown probably would help U.S. butterflies (and moths) too, says Matthew Shepherd of the Xerces Society for Invertebrate Conservation in Portland, Ore. The United States does have some butterfly species with grass-eating caterpillars, such as the grass skipper and the common ringlet.

Whether for butterflies or moths, the study highlights an underappreciated diet. “So often gardeners think about plants and nectar” when planting butterfly gardens, Shepherd says. “That’s great, but it’s not supporting all the life stages of insects.” Often nectar is a grownup food. What caterpillars need is baby food.