Written by Nancy Miorelli
Spring’s right around the corner! Well, for those of us who aren’t heaped under mountains of snow. To kickstart spring, this month we’re going to post all about mantises! So shoot us your questions!
Some of you who may like gardening may be planning on attracting a wide variety of insects to their garden if spring ever dares to show itself. We received a question about attracting mantises to gardens which sparked quite the discussion on Twitter.
In addition I was recently interviewed by the local Audubon Society about beneficial insects and gardening in general for their monthly newsletter. So I though this was a great opportunity to kill two birds with one stone.
What exactly is a predatory insect?
A predatory insect is just an insect that eats other insects or other animals. They’re like the cheetahs and lions of the insect world. Mantises will eat other insects and firefly larva will eat slugs and snails. Dragonflies are great because they eat mosquitoes and ladybugs eat little annoyances like aphids and plant hoppers.
Are there other insects that are beneficial that aren’t predatory?
Yes! Many wasps are harmless to humans but actually lay an egg inside a caterpillar, or another insect host. That egg develops into a larva inside the caterpillar, ultimately killing it. The wasp emerges from the remains of the caterpillar and flies away to mate and lay more eggs. It’s not just wasps either, there’s a fly that decapitates fire ants. Anything that completes its life cycle inside and kills its host is called a “parasitoid”. Also, let’s give a shout out to pollinators as 1/3 of the plants we rely on for food rely on pollinators.
What are some of your favorites and why?
I have so many!! I love mantises because they’re extremely intelligent and have favorite spots where they know they’ll get a lot of food. While strictly not insects, I also have a soft spot for spiders. Not only are they beautiful animals but not all of them spin traditional webs to capture food. Wolf spiders just chase down their prey like cheetah on the Serengeti. Bolas spiders make a silken ball at the end of a line (called a bolas) that has female moth pheromone in it. When a male moth comes over thinking he’s found a mate, the bolas spider will toss the sticky bolas and catch the moth out of the air. Net casting spiders are another creative bunch and swoop up their prey in their silken net.
How do insects help gardeners?
We always talk about environments or ecosystems on the planetary scale like, “the rainforest” or a “desert”. But gardens are ecosystems too. Your garden is a different ecosystem than your lawn, which is different from the woods, which is different from your living room. Gardens have the same things going on in them as a bigger ecosystem just on a smaller scale. Beneficial predatory insects (and others!) are like the wolves and hawks that control pests from the top down. They eat the things you don’t want in your garden. There are even some beneficial herbivores insects used by farmers to control plants.
Which predatory insects should not be picked up with bare hands?
I’m going to expand this to “arthropods” and put a disclaimer that anything with a mouth can bite you. Any of these animals, if not handled gently can hurt. Even mantises can give you a pinch if you’re not gentle! I would suggest not holding centipedes, spiders, or wasps. If you don’t want to sport beetle perfume all day, you might not want to handle them as many can produce strong odors. If you do want to hold an arthropod, gently coax it onto your hand and try not to restrain its movement. Remember, you’re a lot bigger and scarier than you think to small insect or spider.
How do herbicides and pesticides affect these insects?
Generally, there are two types of chemicals used to vanquish undesirables. There are broad spectrum chemicals like Roundup for plants and pyrethroids for insects. They do a lot of damage to non-targets since they use a general mode of action to work. For example, pyrethroids are very harmful to bees. Many beneficial species are more sensitive than pest species to insecticides because of their longer lifespan and reproductive cycle. In fact, even in sub-lethal doses, pesticides have been shown to affect the behavior of bees and spiders. Other herbicides and insecticides are very specific and kill only certain target species. For example, Bt is often used against insects and is readily available. Bt is specific enough to kill caterpillars without hurting their predators.
What are some ways to attract them as well as protect them in your garden?
Planting a wide variety of plants helps attracts lots of different insects. Plants that grow really close to the ground give predatory beetles, like rove and tiger beetles, coverage. Bushes are good for mantises, and anything with flowers attracts a wide diversity of beneficial insects including pollinators and predators. If you look carefully, you should see a wide diversity of bees, wasps, flies, and spiders visiting your flowers. If you have a lot of different things visiting your gardens, you have a healthy garden ecosystem. Making sure your garden has good drainage, and regularly dumping out excess water from birdbaths and flowerpots will deter mosquitoes, which is something a lot of people try and control with insecticides. Many garden stores will sell beneficial insects but not all of the insects are native and not all stay in the area of release. It’s best to read about the insects of interest before buying them.
Why do people sometimes fear these insects?
I think there are a ton of different things going on here. I think the things most people are afraid of are wasps and spiders because they associate them with painful bites and stings. Unfortunately, a lot of people don’t realize exactly how much free pest control these animals give us because they’re so preoccupied with the idea that these animals will just attack you. That usually doesn’t happen without some sort of provocation.
We’re always told through various sources that insects can bite, sting, carry diseases, and destroy crops. They also look very different than things we can immediately relate to which creates a kind of PR problem. I think it’s how we frame them in our minds too. I think people generally have a category for “bugs” in their mind that is already negative, and they slowly start making exceptions to things like dragonflies and butterflies. There have been some great educational campaigns concerning pollinators, which make people view insects in a new light. This sort of positive repeated exposure and education shows people how wonderful and stunningly beautiful these creatures are, and how dependent we are on them. I think that helps people view them in a more positive light.
Do you have a personal favorite anecdote or surprising discovery about predatory insects?
I love examples of predatory insects reversing the food chain. Mantises can catch prey the size of a mouse. Giant water bugs and dragonfly larvae eat fish and frogs. It really shows how complex and variable food webs are.
How important are predatory insects in the food chain? In short, if they were to disappear, why would it matter?
In your garden alone, you can support at least several hundreds of insect species occupying various levels of the food chain. However, the predatory insects are at an interesting spot in the food web. They exert top down control on the things eating your petunias, but also are an important food sources for birds and reptiles. Predators in general promote the growth of biodiversity, the number of species present in an ecosystem. Generally the more species, the healthier the ecosystem. Biodiversity spawns competition, and its predation and competition that keep populations in check.
What are some good websites, books, and other resources to use to learn more about them?
I’m so glad you asked this because there are a lot of resources that push various agendas or spread misinformation. A great book I’d recommend is “Farming with Beneficial Insects” by the Xerces Society. It has good information, pictures of most of the insects, and warns consumers about potential risks of buying insects. If you just want to know what’s in your garden, the “Field Guide to Insects and Spiders of North America” by Arthur Evans is really good. “Bug Guide” is an online insect guide and experts ID photos but it only for North America.
Most of the other resources are fairly informal.
Blogs I’d recommend are:
“The Smaller Majority” by photographer Piotr Naskreki
“Myrmecos” by photographer Alex Wild
“Charismatic Minifauna” by Entomologist and Science Communicator Gwen Pearson
“Beetles in the Bush” by agricultural entomologist Ted MacRae.
“Biodiversity in Focus” by Morgan Jackson
And Nash Turley’s Blog.
Don’t forget you can also contact your local University’s extension entomologists, agronomists, and horticulturalists with any questions.