We’ve been hearing scientific assessments that there has been a massive loss of insects worldwide over the past few decades. My recent personal experience fits right in with this: when I was a child, driving a few miles in the desert or mountains resulted in a windshield covered in the splattered bodies of unfortunate flying insects, but a trip last month all the way to the Grand Canyon only required washing the windshield once. Numbers are clearly down, but diversity is also being affected.
Does this mean we have a real problem and, if so, can we do anything to reverse the trend? The answer to the first question is definitely “Yes”, and it isn’t just that there are fewer six-legged critters around, but what that means in terms of our environment. First, of course, many of them are pollinators, so as they disappear the effect on our crops is being felt. Some pollinate plants that might turn out to be sources of medicine or other products useful to us. Many help to keep the planet clear of debris and dead bodies. And many are beautiful or entertaining to watch.
As the climate changes over an area, so do the maximum and minimum temperatures, the amount and timing of rain, the frequency of damaging fires, winds, and floods, along with changes in soil fertility. All of these affect the ability of organisms to live in that location. These changes may shift the range over which a plant species is found along with the time at which it flowers. Insects may emerge or arrive too early or too late to find sufficient food. This can have an effect on all those animals that eat the insects—other insects, spiders, birds, bats, mammals like raccoons that eat grubs—and on those that eat the insect-eaters—wolves, owls, hawks, and the like. It’s hard to know where the tipping point might be. The problem isn’t new—Thomas Jefferson said: “For if one link in nature might be lost, another might be lost, until the whole of things will vanish piecemeal.”—but it has become urgent.
Some plants depend on only one species of pollinator, and some pollinators are only able to use one species of plant. Some insect larvae feed on only a few types of plants—a familiar case is the monarch butterfly whose larvae can only eat milkweeds. Specialists are obviously more at risk than generalists, and for these individuals, especially those that are rare, habitat loss to agriculture and housing can be devastating, wiping out whole populations.
The common farming method of planting a large area with a monoculture immediately reduces insect diversity. Destroying nearby “weedy” wild areas reduces it even further. Using pesticides and herbicides compounds the problem and can even lead to increased human illness due to this loss of diversity. A recent investigation related to the causes of E. coli outbreaks found that they were often due to contamination of the produce by animal feces (I know, gross, but that’s life). Usual farming practices reduced populations of dung beetles that eat the stuff and of the soil bacteria that break it down. Organic methods didn’t kill off these helpers nearly as much and the produce had much lower contamination.
So, what can we do to slow or reverse the “insect apocalypse”? First, we need to acknowledge the problem and the human contributions to it. We need to evaluate our personal habits to address issues at the local scale, and elect people who will work on the larger scale. We can encourage better farming practices, combat urban sprawl, support actions that slow climate change, and work to preserve natural areas wherever possible. But about that local scale: is there anything specific that we can do in our own gardens?
Indeed, there is. First, plan them for insects. That means plenty of plants to provide food and living space for our six-legged friends. Try to have something in flower most of the year so nectar and pollen are available. Learn to enjoy the holes and tatty edges of leaves as evidence of a thriving urban ecosystem. Wash off aphids, hand-pick snails. If you have insects, you will also have the spiders, centipedes, and birds that rely on them for food. Don’t use pesticides or herbicides unless absolutely necessary and try to buy plants that were raised without the use of neonicitinoids—these all can kill the critters you want along with those you don’t.
Should you go native? Sure, if you want a garden with local native plants, go for it. Many of our local native insects are specialists and are in trouble because their food plants are disappearing. Finding out what these plants are and including them can be very helpful. However, should you uproot all the exotic (non-native) plants that are in your garden? Not if you like them. If they require too much work, water, fertilizer or other chemicals to look good, you should consider their fate seriously, but they aren’t candidates for replacement just because they aren’t natives. Recent studies have shown that the numbers and diversity of insects in a garden are related more closely to having a lot of plants and a long period with leaves and flowers available than they are to the proportion of native plants in the garden. One buckwheat or agave in a sea of gravel will not attract much.
The evidence is clear that major changes are occurring in insect populations, which means the environment is changing in ways that are significantly affecting human populations too. Much of this is do to our actions. We can all help to mitigate these changes and should do what we can to reduce our impact on the environment at every level. In terms of my garden, I will find a spot to plant native milkweeds for monarch larvae (although I will also keep my exotic passionflower for the gulf fritillary butterflies to lay their eggs on). I’ll put out houses for the mason bees and leave some soil bare for ones that nest in the ground. I’ll continue to try to coax more of our natives to grow in my shady garden, but I’ll keep the trees, and continue cramming in plants of all sorts for their beauty, utility, and for the visitors they support!
The Garden Club is a working group of Sustainable Claremont. More articles about sustainable gardening can be found on our website (www.claremontgardenclub.org).