Have you ever wondered what’s happening in your garden while you sleep? It’s probably a lot more than you think.
As the sun goes down and daytime pollinators and predators head to their nests, burrows, hives or roosts, the night shift of insects and other visitors takes over. As darkness slowly envelops your landscape, other strange things start happening outside your bedroom window, too. Leaves begin to change position and flowers that were closed during the day start to open and emit nocturnal fragrances. Think of it as nature’s evening song to lure and welcome the creatures of the night.
“Some flowers specialize in being pollinated by bees, and these will be open during the day,” says Travis Longcore, a scientist at the Urban Wildlands Group, a Los Angeles-based nonprofit that works on conservation and protection of species in urban and urbanizing areas, and an assistant professor at the University of Southern California. “Others specialize in being pollinated by moths, bats or other things, and they will close during the day and open at night.
“So, plants do move. They move in ways that help them take advantage of things in the environment or avoid things in the environment. It’s a form of the general ecological phenomenon known as niche partitioning, which is the dividing up of a resource so different species can utilize different parts of the resource.”
Put another, less scientific way, “It is almost exactly the same as owls being the birds that hunt at night, and hawks being the birds that hunt during the day,” Longcore continues. “If you think about it that way, the night-opening flowers are the owls of the flower world.”
Nocturnal visits guided by the soft light of the moon usually don’t go on all night. The peak of activity is around dusk and just before dawn, conditions of darkness and semi-darkness scientists refer to as crepuscular. “There is actually a series of different nighttime environments,” Longcore says. Organisms tend to divide up their activities to match these changing periods of light and darkness, he adds. That’s not to say no organisms are active in the dead of the night. It just means the greatest activity happens earlier in the evening or shortly before dawn.
The 'pollination syndrome'
Flowers specialized for the graveyard shift tend to have several features in common. They are usually white or a light color such as pale yellow or pink, and often have a musky or even foul odor, sometimes resembling that of rotting flesh. The fragrance helps alert insects to the flower’s presence. When the insect starts searching for the source of the scent, the flower’s light color serves as a sort of beacon that helps guide the insect to the flower’s reward of nectar. As with daytime visitors to your gardens and landscapes, not all nighttime visitors are pollinators and not all are insects.
If a flower is specialized for a special group, this is called a pollination syndrome. Flowers that attract nighttime insects tend to be specialized for their nocturnal interludes in two important ways. One is that they lack the ultraviolet (UV) receptors of flowers that attract daytime pollinators. Because insects see through UV vision, they see flowers differently than we do, points out Longcore. The UV aspect of the flowers guides the insect to the nectar. The second specialization of nighttime flowers is that the nectar tends to be deeper in the flower than flowers that attract daytime pollinators. In some cases, only moths, and some species of bats, can reach this nectar. That’s because they have long a long proboscis, or tongue, that they can unfurl and extend to the place deep in the flower where the nectar is located.
Here's a glimpse at some of the more commonly found pollinating and predatory insects and critters that fit within the pollination syndrome and that might be moving around your garden while you’re sending up zzz's.
You can be excused if you think moths are the most common of the nocturnal insects that visit your garden. After all, as Longcore notes, “They have wings, they flit about and we see them.” But, he’s also quick to point out, “Often in nature it’s the things we don’t notice that are doing a lot of the work.”
Another reason for suspecting moths as the top nocturnal pollinators is that there are so many of them. In fact, there are far more moth species than butterfly species. About 160,000 species of moths exist worldwide, compared with 17,500 species of butterflies, according to the Smithsonian Institution. In the United States, there are nearly 11,000 species of moths, also according to the Smithsonian. Both are in the insect order Lepidoptera.
“If we think about it from a human services perspective, the good side of moths is that they are nocturnal pollinators, and some plants are adapted for nocturnal pollination,” Longcore says. There’s also a bad side, he adds. “There are some common moths that are pests on garden plants. They lay eggs on these plants and then their larvae eat the leaves or stems of those plants.”
Summer squashes are one of those plants, says Lisa Ames, a technician in the Homeowner Insect & Weed Diagnostics Lab at the University of Georgia’s Griffin campus. “Yellow squashes such as crookneck and straightneck are more suited for pollination in the evening and early morning because their flowers tend to shrivel up in heat of the day,” she continues. But these squashes can be difficult to grow in some parts of the country, especially in the South, because of a daytime moth called a squash vine borer.
“This moth lays its eggs on the stems of the squash plant," Ames says. "You won’t know the eggs are there because they are hard to see. When they hatch, the larvae bores into the vine-like stem and eats it. One day you will have a beautiful looking squash plant and the next day the will be dead or dying."
But from a sort of ecological gardening perspective, there can be an upside to pests such as the squash vine borer moth because they attract birds to feed on the eggs and larvae, Longcore says. “So, it kind of depends on your perspective, whether you see [certain actions] as a service or as a disservice.”
In the Eastern United States, one of the most effective pollinating moths is also considered a pest. That’s the tomato hornworm, which is active both during the day and at night. This is one of the largest hawk moths and is considered a pest because it eats tomatoes.
Recent studies have shown that moths are facing a man-made problem other than pesticides to control the ones that are garden pests. That’s streetlights. “There is quite a bit of research recently coming out about pollination service and the decrease in pollination when you have artificial lighting that keeps the moths from being as active,” Longcore says.
A squash bee, Xenoglossa strenua, pollinates a plants before other bees even start working for the day. (Photo: USGS Bee Inventory and Monitoring Lab/flickr)
The squash bee is an exception to the rule that bees are daytime foragers. In fact, squash bees can typically pollinate a plant (or a field of plants) before other bees have even begun foraging for the day, according to N.C. State Extension.
Squash bees pollinate flowers exclusively in the genus Cucurbita — summer squash, winter squash, zucchini, pumpkins and many gourds (but not cucumbers) — and are crepuscular in the sense that they are active before or beginning at sunrise, which is when squash flowers open. The flowers wilt in the heat of the day, typically around noon, Ames says. Squash bees begin visiting the flowers when they open, before many alarms have gone off or gardeners have had their first cup of coffee. Squash bees nest in the ground near squash plants.
“We are used to the European honeybee,” Longcore says, “but from an ecological gardening perspective we should be concerned about and trying to encourage all of the solitary native bees that we have here in North America. They would be much less susceptible to collapse if we provide the habitat for them and avoid the pesticides that kill them.” Solitary bees do not live in colonies like honeybees or bumblebees. Rather, female bees build a nest, usually in the ground or a hollow branch or stem, and collect pollen and nectar to feed their young.
The next time you think about swatting an annoying fly, consider this: Flies are second in importance to bees as pollinating insects.
Flies, which are in the order Diptera, can be both nocturnal and diurnal pollinators. “They are just sort of part of the system of consumption and recycling of stuff,” Longcore says. “The fly larvae, which people like to refer to as maggots, are very useful in breaking down dead material and recycling those materials back into the soil and enriching the soil.”
Beetles can be active at night and some are pollinators, Longcore says, as they crawl up between the flowers and eat pollen. They are also part of the food chain in terms of breaking things down, and their larvae may grow in downed wood, dead vegetative matter or in the soil.
All beetles can fly and, like many other insects, they use nectar for flight energy. Carpet beetles are an example of a common beetle group that includes nocturnal as well as diurnal species, Ames says. “The ones that are active at night like white flowers.”
Carpet beetles are also a common household pest. While they naturally occur outdoors and feed on nectar and pollen, their larvae feed on fabric. Adults can enter homes and businesses fairly easily through improperly sealed doors and windows or even small cracks and crevices.
The fierce-looking rhinoceros beetle is another example of a nocturnal beetle. It has a relatively large body, up to 6 inches long. Males have a horn-like projection on their heads. They hide out in fallen plant material during the day and feed on fruit, nectar and sap at night. Rhinoceros beetles, which are sometimes kept as pets in Asia, are found in the United States in the South from Arizona northeast to Nebraska and eastward.
While fireflies in the Eastern U.S. are famous for scenes like this, Western varieties tend to be subtler. (Photo: Matt MacGillivray/flickr)
Fireflies are often called lightning bugs, but they are actually beetles. There are at least 170 species in the United States. The ones you see flying around in the evening and sending out their trademark yellow flashes are males. Females are usually resting on nearby stems or leaves and will send flashes of light back to the males.
There can be more than one species and they are dividing up the dusk according to their preference, Longcore says. “What this means, and there are other species that do this as well, is that they have sort of peak activity periods. If you have nighttime lighting that keeps it from ever getting darker than a certain illumination, those species never get their optimum conditions to happen so you can actually eliminate them in that manner.”
Light pollution, for instance, is a source of population declines that have been reported in recent years. Habitat loss and a reduction in water tables are also said to have contributed to a reduction in their numbers. Their optimum habitats, Longcore says, are wet meadows and grasslands.
Fireflies are also pollinators, especially for plants such as milkweed, goldenrod and species in the native sunflower group. Their larvae, which live in the ground, also provide an important service. They eat pests such as slugs, snails and aphids. The adults, conversely, can be a food source for bats.
Snails and slugs
Who hasn’t walked out into their garden in the morning and seen the slime trail evidence that a slug has crossed a walkway on its way to forage on your plants? “While they may be out during the day when it’s wet or in wet environments, they usually are restricted to the nighttime because of its increased humidity and cooler temperatures,” Longcore says. While he acknowledged they are important in terms of breaking things down, they can also be a pest.
That’s because slugs — soft-bodied mollusks without a shell — will chew unsightly holes into almost any vegetation in your ornamental or vegetable garden, as well as eat fruit such as strawberries and tomatoes. They are especially attracted to tender emerging leaves. And they can hide almost anywhere that's dark and damp. Some of their favorite refuges are to under pots, rocks and boards where they often go undetected during the day.
Some DYI methods to kill them include leaving out a saucer of beer for them to crawl into and drown, placing some cornmeal in a jar turned on its side (it will expand inside them when they ingest it) and putting crushed eggshells around prized plants (they won’t cross the eggshells because of the sharp edges).
Snails cause similar problems to the damage wreaked by slugs. One snail pest in particular is the brown garden snail (European brown snail), Cornu aspersum. It was introduced to California in the 1850s from France as a source for escargot. It has thrived there, where it is considered a true pest. Its range now extends to the Southeast and northward to New Jersey, according to the University of Florida, although it is not considered to be the same threat to crops elsewhere as it is in California.
It's not usually good news when you see carpenter ants inside your home. (Photo: Sancho McCann/flickr)
“Carpenter ants are active at night and like to get into flowers where they seek honey dew from aphids and scale insects,” Ames says. They are most active in spring and summer and between sundown and midnight.
They get their name from their habit of building nests in moist wood or wood that’s partially decayed. Favorite nesting spots include tree stumps, hollow logs, wood piles, fence posts or dead portions of standing trees. Workers can travel the length of a football field in search of food.
If you find them in your home, there’s a good chance they are simply looking for food. Favorite choices include something sweet in a pantry or on a counter top that wasn’t cleaned well.
Carpenter ants can also build nests in your house, although these nests do not tend to be as large as outdoor nests. Potential indoor nesting spots include areas that are damp from leaks, such as under kitchen and bathroom sinks, or in wood that is moist from a leak in the attic. They can cause structural damage, though this doesn’t tend to be as severe as the problems caused by termites.
If the sound of crickets is music to your ears on a summer night, it may be a sad song they are singing to you from your garden. “There’s a lot native crickets as well as introduced crickets across North America, and they eat vegetable matter,” Longcore says. While that helps renew minerals in the soil, it doesn’t do much for the appearance of the plants they are eating.
The crickets you are hearing, by the way, are males. They make their chirping sound by rubbing their wings together to attract females and warn competing males not to enter their territory. After mating, they chirp another song to signal their success in attracting a female.
Unlike most stinging insects, the European hornet is active at night. It was brought into the United States in the New York area in the 1800s and has spread to more than 30 states. In addition to tree sap and fruit, it also feeds on honey dew from aphids and scale and in the process can pollinate flowers, Ames says.
These hornets live in colonies that can number several hundred. They sometimes find their way into houses where they build nests in hollow walls. They can be dangerous if disturbed because they have a smooth stinger without a barb that allows them to sting their victims repeatedly.
Everyone knows bats are valuable for feeding on pesky insects such as mosquitoes, but far fewer people may know that bats provide important pollination services. Worldwide, more than 500 species of flowers in at least 67 plant families rely on bats as their major or exclusive pollinators, according to Bat Conservation International.
When it comes to home landscapes, bats in the United States are most valuable in Western gardens that have cactus or agave plants, Longcore says. Bats also play an important role in commercial farming (and not just by eating crop pests). If you like a margarita or are a chocolate lover, you can thank a bat. They are pollinators of cocoa, from which chocolate is made, and agave, from which tequila is derived.
How to attract night pollinators
“My general rule for gardens is that you have a much greater probability of attracting pollinators if you use plants that are native to your particular region, whether you are talking about daytime or nighttime pollinators,” Longcore says. “But there are some things you can do slightly differently to target nighttime pollinators,” he adds. Those include:
- Pick plants that have night-opening flowers, especially flowers that are white or light-colored and have a musky fragrance.
- Avoid insecticides.
- Accept the possibility that it may be a good thing if you have insects eating a little bit of your plants. If you can do this, then you can begin to understand the beauty of a garden is not in perfectly shaped leaves and beautiful flowers. When you see plants that are being eaten by other things that means you have a living, dynamic and changing landscape that will attract birds and other members of the food chain.
Perhaps the most important thing you could do to attract nocturnal visitors, though, falls into an area that is a research specialty for Longcore: ecological light pollution. “Let’s imagine people want to encourage nocturnal life in their gardens but they also want to do lighting,” he says. “I have a few rules of thumb for that. There is a report that we did for the National Park Service that goes through these rules for protected areas, but they really work to minimize the effects of light in a domestic garden as well.” Those rules are:
- Don’t put lights where you don’t need them.
- Turn lights off when don’t need them. You can do this with motion detectors and timers.
- Keep the lights pointed at the object that needs to be lighted instead of out into people’s eyes or up into space, which is called shielding. You really shouldn’t see the light bulb. What you should see is the effect of the light. Some people think they are safe when they see light from a bright bulb, but what they are getting is a lot of glare that makes the shadows look darker and makes it easier for people to hide.
- Use only as bright a bulb as you need.
- Use a bulb with a good spectrum of light. This is especially important for people who garden. It’s better to use lights that resemble the good old fashioned bug lights, which are appropriate because they are yellow. Even though the light isn’t great for our purposes, it’s usually good enough to see by and to give you the safety you seek while minimizing the numbers and types of insects it will attract.