Insects of the Arboretum B Y P ATRICK C . T O B IN et’s face it. When most of us think of insects, we think of pests. In fact, the very definition of “pest” from the Webster’s dictionary includes the word “insect.” But out of the more than one million described species of insects, only about one thousand—one tenth of one percent—are Lconsidered to be serious pests, and only ten thousand, or one percent, are considered to be even occa- sional pests. So what exactly are the rest of these insect species doing if they are not damaging our crops or sucking our blood? It turns out that in addition to not being pests, they are also engaged in extremely beneficial activi- ties. We are fortunate that many beneficial insects make their home in our region, where they perform important services such as pollination, pest control, and the breakdown of organic matter. Following are profiles of some of the beneficial insects and other invertebrates found in Washington Park Arboretum during recent “bioblitzes” (biological surveying events) coordinated by the University of Washington. There’s a good chance you might encounter some of them in your own backyard, too. Giant western crane fly. Western fairy lady beetle. (Photo courtesy Jim Moore) (Photo courtesy Andrew McKorney) GIANT WESTERN CRANE FLY cranefly species feed on the roots of turf grass HOLORUSIA HESPERA and are considered pests.) The giant western crane fly, Holorusia hespera, With a wing span of about three inches and might look like an enormous mosquito—but, a body length of an inch and a half—not includ- thankfully, this native species has no interest ing the legs!—Holorusia hespera is the largest in drinking human blood. In fact, crane flies, crane fly in North America. Crane flies belong to though closely related to mosquitoes, gener- a unique insect order called Diptera, a name that ally do not eat as adults. They do all their eating translates to “two wings.” Insects in this order— during their larval stage and spend most of their including house flies—are the only insects with adult life (about two weeks long) looking for a one pair of wings, whereas all other insects mate. And what do the larvae eat? The grayish- have two pairs of wings, or are wingless (such brown grubs are primarily associated with rivers as fleas). Where did this other pair of wings go? and streams, where they consume leaf and Well, the back pair of wings evolved into special- other plant debris. (Although the larvae of a few ized club-like structures called halteres. The 8 v Washington Park Arboretum Bulletin structures (which are easy to see on Holorusia bacteria or otherwise—is thought to be a beetle. hespera because it’s so big) move like a gyroscope They owe some of their success to their wings. and help to stabilize the flies when in flight. Beetles, like most insects, have two pairs of wings. Crane flies are clumsy fliers as it is; without their However, beetles only use one pair (their hind halteres, they’d be truly ungraceful in flight! wings) for flying. The other pair (the forewings) are as hard as the rest of their outer body parts. WESTERN FAIRY LADY BEETLE The role of the forewings is to protect the more PSYLLOBORA BOREALIS fragile, membranous hind wings. This extra layer of protection serves the beetles well, as without The western fairy lady beetle is native through- their wings and the ability to fly, insects can easily out western North America, including the Puget become prey or fail to find their next food source. Sound region and the Arboretum. It belongs to the same insect family (Coccinellidae) as lady- YELLOW-SPOTTED MILLIPEDE bugs, which we often associate with eating aphids HARPAPHE HAYDENIANA and occasionally trying to spend the winter in the comfort of our homes. The western fairy lady Although not an insect (which typically has just beetle, however, likes to spend its winters out- three pairs of jointed legs), the yellow-spotted side in small groups in leaf litter. As for its dining millipede, Harpaphe haydeniana, plays an impor- habits, it belongs to a lady beetle group that does tant role in the Arboretum. Unlike centipedes, Yellow-spotted millipede. (Photo by Walter Siegmund/ Hover fly. (Photo by Joaquim Alves Gaspar/ Wikimedia Commons) Wikimedia Commons) not eat aphids but rather prefers to feed on fungi, which are largely predators, millipedes are detri- especially fungi growing on plants. Thanks to our tivores (organisms that feed on dead organic region’s long, rainy, overcast season—lasting matter, such as fallen leaves or dead plants). Thus, from fall to spring—there is no shortage of fungal they serve a critical role in breaking down organic plant pathogens here! One such group of fungi matter. The world would be a much different are the powdery mildews, which are often the place—and likely covered in dead animals and bane of gardeners and commercial farmers. Some plants—if not for detritivores! The breakdown entomologists have proposed using the western of organic matter also releases back into the soil fairy beetle as a natural control for powdery mil- vital nutrients that living plants need for growth. dews; so, these insects are undoubtedly beneficial, Contrary to their name, millipedes do not and we should welcome them in our landscapes. have a thousand legs. In fact, the number of legs Beetles as a group are the most numerically on a millipede ranges from 40 to 400, depend- dominant organisms on Earth: Nearly one out ing on the species. Millipedes differ from their of four of all species—whether animal, plant, centipede relatives by the number of legs per Summer 2018 v 9 segment: Centipedes have two legs per segment, These insects are extremely beneficial in the while millipedes have four legs per segment. The Arboretum and beyond. As the common name yellow-spotted millipede, which is native to the “flower fly” implies, they generally feed on nectar Pacific Northwest, has 60 legs if male and 62 and pollen from flowering plants, and conse- if female. Not quite a thousand, but certainly quently are extremely important as pollinators. enough to get it where it wants to go! It has few Recent estimates suggest that up to 87 percent of predators due to its ability to secrete hydrogen the world’s flowering plants depend on animals, cyanide when threatened (another common name and especially insects, for pollination services. is cyanide millipede). The amount secreted is not Without these hover flies in the Arboretum, there enough to seriously harm a human (although it might be a lot less fruit on the trees for resident may stain the skin or cause some blistering), but birds and other wildlife to feed on! it can be lethal to birds and rodents. SNAIL-EATING GROUND BEETLE HOVER FLIES, FAMILY SYRPHIDAE SCAPHINOTUS SPECIES Hover flies from the insect family Syrphidae Ground beetles are a very large and globally dis- might cause alarm at first glance. This is because tributed insect family, and species in this family many are mimics of bees and wasps. The bright can be predators, herbivores, detritivores and colors of many species of bees and wasps serve as omnivores. Beetles in the genus Scaphinotus are Snail-eating ground beetle. (Photo by Walter Siegmund/ Common pillbug. (Photo by Walter Siegmund/ Wikimedia Commons) Wikimedia Commons) a warning to potential predators: “Come near me, snail eaters, and there are 55 species of them and I’ll sting you!” (The bright markings on the native to North America, including several in our yellow-spotted millipede flash a similar warn- region. As their common name implies, they eat ing.) However, some species mimic these colors land-dwelling snails. But snails are not always even when they lack such formidable defense. such easy prey as they can retract themselves into Hover flies, also known as flower flies or syrphid their hardened shells. What’s a beetle to do to get flies, are such mimics and are closely related to a meal?! the common house fly. Many hover flies look like Well, Scaphinotus beetles have overcome this bees and wasps, but rest assured, they lack any challenge through a modified body shape and type of stinger. Hover flies, like the giant west- mouth. The body of these beetles is curved, much ern crane fly, are in the order Diptera and thus like the curvature in the snail shell. In addition, also have two wings, with a pair of halteres, and the mouth is quite elongated and shaped much this feature can be used to distinguish them from like a snail fork that you might use while dining four-winged bees and wasps. on escargots. The adaption allows this group of 10 v Washington Park Arboretum Bulletin beetles to consume the otherwise protected snail lichen and algae, too. This particular species, and is a great example of how insects can evolve Armadillidium vulgare, is not native to our Pacific to survive on a highly specialized diet. It’s also Northwest ecosystems but rather is a European a great example of how having a diverse suite of species, likely introduced during colonial times. insects in your garden can help keep pest popula- The common pill bug is found on all continents tions under control! except for Antarctica. They particularly thrive in moist climates and damp soils, making our COMMON PILLBUG region an ideal habitat. It is not known whether ARMADILLIDIUM VULGARE this non-native species is invasive—in terms of The common pill bug, Armadillidium vulgare, displacing native species—but we do know that it belongs to a group called the woodlice, is present throughout the United States in fairly which include pill bugs and sow bugs.