True bugs

Beware the piercing mouthpart.

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Alydus eurinus is a "broad-headed bug" currently very common on the Vineyard. It is herbivorous, feeding on juice and sap from various legume species.- Matt Pelikan

As informal shorthand for nearly any kind of insect, the word “bug” gets used by pretty much everyone. Serious entomologists sometimes even make a verb of it — “bugging” — to describe the activity of hunting for insects. But it’s worth knowing that the word has a more precise meaning (though still informal): It refers to members of the insect group Heteroptera, also known as the “true bugs.”

Formerly considered an order of its own by biologists, Heteroptera was recently downgraded to “suborder” status, lumped with cicadas, aphids, and leafhoppers in the very large order Hemiptera. This is a polite way of saying there is lot of confusion around the relationships and evolutionary history of these insects! But whatever its official standing, Heteroptera is a group with a fairly distinct identity.

Bugs in this sense are small to medium-size insects, generally with flat and wide bodies (sometimes almost as wide as long). Heteroptera, like the rest of their newly expanded order, practice what is called gradual or incomplete metamorphosis. In contrast to, say, butterflies, which start as caterpillars before morphing into a dramatically different adult form, bugs start out as nymphs that are essentially small versions of their adult selves. As they mature, they grow larger, develop wings, and acquire the apparatus they need for reproduction. But the similarity between nymph and adult is often close enough so that nymphs can be identified, if you’re familiar with the adult.

True bugs have a complete set of four wings (unlike flies, which have just two), and the foremost pair are generally thickened and serve as a protective layer (though less robust than that of a beetle) over the membranous hind pair, which are the main source of propulsion for flight. Bugs also possess what biologists term “piercing mouthparts,” meaning stout, straw-like organs that can penetrate food items. It’s a versatile sort of tool, and across the more than 42,000 species of heteropterans in the world, these beaks are used for everything from sucking juices from plants to impaling and draining other insets, to — in a few cases — sucking blood from mammals or birds. It’s a great example of a basic design that is so efficient it has evolved to serve a wide range of functions.

The most dramatic species among the true bugs are surely the predatory ones, most of which are lumped under the common name “assassin bugs.” (Formally it’s a subfamily, Reduviidae, and a rather small group, with fewer than 200 members in North America.) The business end of these insects, which varies widely in overall shape and appearance, features a robust spike that is generally carried tucked up under the face and body of the insect. Deployed for use, it’s a formidable weapon; assassin bugs drive this “piercing mouthpart” into their prey, which may be nearly any sort of insect, and inject a mix of enzymes that rapidly immobilizes the prey and breaks down its proteins. The predator then drinks its prey through the same organ it used to kill.

Assassin bugs are masters of stealth and concealment. One subset, the ambush bugs, have evolved to resemble flower parts, and they are easy to overlook as they wait for prey on a blossom. Predictably, they tend to take pollinators: Bees, certain kinds of beetles, and flies. Other assassin bugs, like the common and widespread species Zelus luridus, seem to prefer perching on leaves. They move dexterously around, often peeping around the edge of a leaf or through a hole chewed by some herbivorous insect to catch their prey by surprise. Assassin bugs have no interest in attacking people — we’re far too large for prey — but they are not bashful about jabbing you if you grab them, and reportedly such bites hurt worse than wasp stings.

Most true bugs, though, are less pugnacious. Many kinds use their mouthparts to pierce tender plant tissues, living on the juices they draw from the plant. In some cases, these herbivorous bugs can be common enough to damage plants through their collective feeding. Perhaps a greater problem may be the secondary effects of stem-piercing: making the plant vulnerable to infection. For example, squash bugs, in the genus Anasa, are regarded as agricultural pests. Other Heteroptera specialize in eating seeds — two very common common red-and-black bug species, for example, are called milkweed bugs and are found on a high percentage of milkweed flowers and seed pods.

Another unappealing feature of many true bugs is the ability to exude foul-smelling substances when disturbed. This talent, useful for self-defense, is most prevalent among the family Pentatomidae, members of which have earned the common name “stink bugs.” But in fact many other true bugs are equipped with scent glands, and some of them smell a good deal worse than most official “stink bugs” do!

So a good rule of thumb is not to handle any true bug unless you do it carefully and know what it is. But like any other group of insects, Heteroptera are simply part of the complex web of nature — except when they’re actively harming valuable plants, they should be left alone to carry out their natural roles.