Boxelder Bug

 


I was playing outside with my dog the other day and found this little fellow on the side of our house - an eastern boxelder bug (Boisea trivittata). As the name implies, these colorful insects are members of the order Hemiptera (commonly referred as the true bugs) which feed primarily on boxelders (Acer negundo). As it turns out, finding them on the side of your house is not at all unusual, as they like to sun themselves on the sides of buildings on cool or windy days in the fall and early spring (Evans 2008). What is apparently unusual is finding only one - if a spot is especially good for sunning and is close to their host tree, they will often gather there in very large groups. I guess I'll be back with more pictures if that happens. 

In addition to boxelders, boxelder bugs will also feed on other trees in the maple family, as well as oaks and ailanthus. When I read this, I was a bit worried - we have a beloved red maple right behind our house - but it turns out that they are not usually considered significant pests of maples or any other tree. This is because boxelder bugs mostly feed only on sap located in the seeds and flowers of their host trees, and even when they do attack other parts of the tree, they tend not to cause much damage (Evans 2008). Overall, given the warm surface of our house and a big, healthy red maple covered in seeds right nearby, it sounds like this little guy was living it up!


Plants and Insects: A Special Relationship

Here's a question for you - how many different species of Lepidopterans (that is, moths and butterflies) do you think are supported in some way by maple trees? 

The answer, according to a review paper published by ecologists Douglas Tallamy and Kimberly Shropshire in 2009 is around 297, as least in the Midatlantic region of the U.S. The paper also estimates the number of Lepidopterans supported by members of nineteen additional genera in the region, including oaks (534 species), cherries (456), birches (411) and pines (201). 


The larva of the rosy maple moth (Dryocampa rubicunda) feed almost exclusively on maple trees (1)

And this only the tip of the iceberg - from true bugs, like the boxelder bug, to bees, beetles, and mites, there are thousands of species of North American invertebrates that feed on or otherwise depend on plants in some way. Of these, a great many are generalists, meaning that they will eat just about any kind of plant that they can get their mandibles on. Others are specialists, meaning that they will only feed on members of a single group of plants or even a single species. This also applies for many predatory or parasitic insects - some will eat pretty much anything that will fit in their mouths while others, especially parasitoids, will only attack members of particular groups or species.  

While some groups of plants, including several of the ones on Tallamy and Shropshire's list (Narango et al. 2020), support especially rich communities of herbivorous (plant-eating) insects, just about all plants seem to have at least one or two species that specialize to some degree in eating them. After all, specialization can be an excellent strategy for avoiding competition - if a plant is unappealing to the majority of herbivorous insects, any species that can find a way to exploit it will have a food source all or mostly to itself. Plant diversity is thus an important driver of insect diversity, as herbivorous insects evolve to specialize in eating a particular plant and predators and parasites specialize to attack the herbivores. This relationship between plant and insect diversity has even been used by scientists to try and estimate the total number of insect species living on the planet (Stork 2018). 

The special relationship that exists between plant and insect diversity is also why many conservationists advocate for planting native species in gardens. Exotic plants can and often do support a number of generalist insect herbivores and pollinators - the cone flowers planted around my neighborhood, for example, are often swarming with bees, skippers, hoverflies, and even goldfinches - but when it comes to specialists, they are much less popular. This is because they have, for the most part, left their specialists behind in their native range. Native species, on the other hand, can readily attract a variety of generalist and specialist species that they have been evolving side by side with for thousands of years.

So, if you are looking to put in some new plants around your home or workplace, consider some native species - maybe you'll attract some cool insects like the boxelder bug! Do be warned thought that boxelder bugs will sometimes overwinter inside buildings if they can find a way inside, so if you've had trouble with insects getting into your home in the past, maybe avoid maples. 


Sources:
Evans, A.V. (2008). Field guide to insects and spiders of North America. National Wildlife Federation, p.128.

Narango, D. L., Tallamy, D. W., & Shropshire, K. J. (2020). Few keystone plant genera support the majority of Lepidoptera species. Nature Communications, 11(1), 1-8.

Stork, N. E. (2018). How many species of insects and other terrestrial arthropods are there on Earth? Annual review of entomology, 63, 31-45. 

Tallamy, D. W., & Shropshire, K. J. (2009). Ranking lepidopteran use of native versus introduced plants. Conservation Biology, 23(4), 941-947. 


Photo Credits:
(1) "#7715 - Dryocampa rubicunda - Rosy Maple Moth" by Andy Reago and Chrissy McClarren CC BY-2.0




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