A new study suggests that road salt – often seen as harmful to bugs, plants and fish – might actually make for stronger butterflies.
University of Minnesota ecology professor Emilie Snell-Rood published a paper in this week’s Proceedings of the National Academy of Sciences about the effects of road salt on butterflies.
Snell-Rood says she got the idea for the study when she moved to Minnesota and saw all the salt that was being put down on local roads.
“I knew that sodium was a really important micronutrient in a lot of animals,” she says.
Vital for nerve and muscle development, sodium is often in short supply in nature, which has caused some animals to adopt odd behaviours – moose eating salty aquatic plants, for example, or butterflies gathering at mud puddles. Host plants for butterflies, particularly milkweed, are often found along roads, meaning they can absorb salt-laden runoff.
Snell-Rood and her team tested the effects of salt on monarch and cabbage-white butterflies. Monarchs were raised on milkweed plants taken from next to and 500 metres from a road where salt was applied. Tests showed that the milkweed plants taken from next to the road had about 16 times more sodium in them.
Cabbage-whites were raised on wheat germ and agar samples with different sodium levels.
Just 41 per cent of monarchs and 11 per cent of cabbage-whites survived to adulthood when raised on high sodium diets compared to 58 per cent and 42 per cent for those raised on low sodium ones, the team found.
But those that survived on high sodium food appeared to benefit from it. Males had more developed flight muscles, which could help them fly longer to find mates, while females had bigger eyes and brains, which could help them find places to lay eggs.
It’s tough to say if these effects actually help butterflies on a population level, Snell-Rood says. If butterflies gather around roadsides to exploit salty plants, they could die more often from vehicle collisions, for example. It’s also clear that higher sodium levels are toxic to these bugs.
City residents can spruce up their gardens by getting bugs to do their dirty work, says Edmonton’s chief bug guy.
City of Edmonton biological science technician Mike Jenkins is co-hosting a talk next Tuesday with YEGBees representative Mike Hamilton on beneficial backyard bugs.
“The vast majority of the insects that are in our backyard are either neutral or largely beneficial to us,” Jenkins says.
Spiders and beetles will eat many cutworms and slugs that attack garden plants, for example, while bees and mosquitoes can help with pollination. Parasitic wasps will also lay their eggs in pest insects, reducing their numbers.
“Some of them are incredibly tiny,” Jenkins notes – smaller than the size of some insect eggs.
But most pesticides kill off all these bugs as well as the pests they’re meant to target. Moreover, pests such as aphids tend to reproduce faster than the predators that eat them, meaning you can end up with more pests at a time when you’ve fewer predators to deal with them.
“In a lot of cases, using these broad spectrum pesticides can actually make a pest problem worse,” Jenkins says.
Jenkins suggests planting low-lying plants such as thyme to provide cover for spiders and beetles, and having plants with lots of tiny flowers, such as dill, to draw small wasps.
You can also create a pollinator block.
“You take a piece of wood and drill a whole bunch of holes into it,” Jenkins explains.
These blocks should attract bugs such as carpenter bees, which will hang out in the holes instead of chewing new ones in your deck.
The talk runs from 7 to 9 p.m. in Room 1-121 at the University of Alberta’s Edmonton Clinic Health Academy this June 17. Entrance is by donation to the Prairie Urban Farm.
Visit prairieurbanfarm.ca for details.
