What kind of bug is a bug?

Giant milkweed bugs – adults and nymphs – on butterfly milkweed, Lincoln Creek Prairie, Aurora, Nebraska.

The term bug gets thrown around a lot, and in common language refers to just about any insect or insect-like creature. Technically speaking, (donning my nerd hat) true bugs are only those insects in the taxonomic order Hemiptera, suborder Heteroptera. Of course, we used to be able to say that true bugs included anything in the order Hemiptera, but as you may know, that order now includes hoppers (suborder Homoptera) – including cicadas, leafhoppers, etc.. It also includes insects in the suborder Sternorrhynca, which includes aphids, scale insects, mealy bugs, and others. All of this is obviously information you can easily apply in your daily life and conversations.

Example: (standing at the water cooler) “So hey, Joe, don’t you think it’s crazy that mealy bugs are Hemipterans now? It’s just weird, right?” (Joe punches you in the stomach and gives you a wedgie)

Ok, but whether or not your knowledge is appreciated by others, sometimes it’s just nice to know things. So if you’re interested, here are some tips for distinguishing true bugs from other insects.

Heteropterans are characterized by a few different features. The easiest to see in the field are located on its back. Adult true bugs have a triangle structure (scutellum) between their wings. Technically, that triangle is located right behind the pronotum, which is the structure right behind its head. The triangle can vary greatly in size and shape, but it is (nearly?) always there, as long as the bug is a full adult. We’ll talk nymphs later…

Stink bug on wavy-leaf thistle at Griffith Prairie, north of Aurora, Nebraska.

The other distinguishing features on a bug’s back are its wings, which are crossed over each other at rest. The base of each wing is thickened and solid, but the tip is membranous and often transparent. As a result the folded wings have a two-toned appearance, which, combined with the triangular scutellum, is fairly easy to recognize. (Bonus knowledge: bugs actually have FOUR wings, but you rarely see the other two unless the bug is flying or dead, which doesn’t help much when you are trying to identify a little critter scurrying away from you.)

Assassin bugs mating on annual sunflower. The Nature Conservancy’s Niobrara Valley Preserve in north-central Nebraska.

For comparison, beetles (which are NOT bugs) have two hard shells, called elytra, covering their wings. When they fly, they have to lift those elytra up out of the way. This makes them look a little like a DeLorean with its doors open.

These four beetles all have the hard wing coverings (elytra) that help distinguish them from bugs. They include (clockwise from top left) a long-horned milkweed beetle, scarab beetle, soldier beetle, and lightning bug/firefly, which is neither a bug nor fly.

The other characteristic of bugs to look for, if you have the opportunity, is the mouth. True bugs have a long segmented proboscis, through which they suck up their food. This feature can be helpful in distinguishing bugs from beetles, which often have distinct mandibles, but not so much from creatures like cicadas, leaf hoppers or other Hemipterans (see first paragraph), which also have sucking mouthparts. When feeding, a bug will insert its proboscis into a plant (or, in some cases, another insect). The rest of the time, bugs keep their proboscis tucked up underneath their body, making it difficult to see.

Wheel bug (a true bug) in the Loess Hills of Iowa. Wheel bugs and their close relatives assassin bugs and ambush bugs often have more prominent mouthparts than other bugs, which makes them easier to identify as true bugs.
Stinkbug with extended proboscis on Illinois tickclover (Desmodium illinoense). Deep Well Wildlife Management Area, Nebraska.

Immature bugs can be a lot more difficult to identify. Bugs go through incomplete metamorphosis; they start as an egg, hatch as a tiny nymph, then molt several times as they grow before their final molt into an adult. If you’re hankering for another wedgie, the technical term for this life cycle is hemimetabolous.

Nymphs of giant milkweed bugs – Lincoln Creek Prairie in Aurora, Nebraska.

Nymphs resemble adults fairly closely, but have only little stubs for wings (which get longer as they grow and molt). Bugs don’t get functional wings until their final molt into adulthood. Besides limiting their movement, this lack of full wings also makes bugs hard to identify using the earlier tips. You can still look for their proboscis to distinguish them from beetles, but otherwise identification is tough, unless they happen to be clustered around adults of the same species.

Knowing that the term bug applies only to a select group of insects is helpful. Whenever you hear someone use the word colloquially, referring to a beetle, grasshopper, or even spider, you can smile smugly to yourself. In the right situations, you can even make a helpful correction, spreading your knowledge around a little. Just be careful of your audience. Smug corrections to the wrong people can lead to some significant discomfort in your lower torso…

Filling in gaps in the dragonfly migration story

Insect migration has long been fascinating to me. I’ve written several posts on this before, including one on migrating moths and one on painted lady butterflies. We’ve long known that many dragonfly species are long-distance migrants, including the large charismatic green darner. Citizen science records have helped document that migration, but there have been many questions about the details. A new study has now cleared up many of those questions, revealing a fascinating story.

Common buckeye butterflies don’t overwinter in Nebraska. We only see them after they migrate northward into Nebraska each year.

Green darner dragonflies (Anax junius) is a common species here in Nebraska and throughout much of North America. For years, we’ve known that the species migrates because people have kept track of when large flocks (herds? squadrons?) are sighted each year. However, green darners can also overwinter in the northern U.S. as aquatic nymphs (their immature stage). The speed of development for an egg apparently depends upon temperature and photoperiod (day length). Some eggs develop quickly into nymphs, which quickly grow and molt into adults. Others develop very slowly and enter diapause (dormancy) over the winter months, emerging the next spring to become adults.

A recently emerged green darner and the empty shell of its nymph form.

The authors of the new study (read it HERE) combined citizen science observations with stable isotope analysis to piece together the migration story of the green darner. What they found was an annual cycle comprised of at least three generations. The first emerges in the southern part of the continent between January and May and migrates as far as the northern edge of the U.S., where the dragonflies lay eggs and die. A second generation emerges in the north and migrates back south late in the year. That second generation includes darners that were born the previous year and overwintered in the north, as well as others that hatched and matured within the same season. When fall migrants arrive in the south, they lay eggs that grow up to form a non-migratory population. The individuals in that population live their whole life in the same general area. The eggs laid by that non-migratory generation become adults that migrate back to the north in the spring.

So to summarize, if you’re a dragonfly whose parents migrated south, you will grow up into an adult that lives its entire life in the south without migrating. However, your kids will migrate to the north where they will lay eggs before they die. Those eggs might turn into adult dragonflies that same year or they might not become adults until the following year. Either way, those new adults will migrate back to the south where they will become the parents of another non-migratory population.

Face to face with a green darner dragonfly.

It’s exciting to better understand the migratory patterns of the green darner. Hopefully, we can get more information on the many other migratory insect species soon. Knowing how and when insects migrate is, of course, fascinating in its own right, but there are also practical conservation implication. That information can inform the way we manage individual sites to ensure management actions don’t interrupt insect cycles at critical points. Even more importantly, understanding migratory patterns helps us consider how climate change might affect them. Temperature shifts and increasing intensity/frequency of droughts are both factors that could potentially have large implications for migratory dragonflies and other insects.

Insect migration is just one of many phenomena we still have much to learn about. On the one hand, it’s invigorating to know there are still plenty of unexplored frontiers out there for scientists studying natural history. On the other, there’s a sense of urgency about getting those data so we can act on them. Either way, I’m grateful for those scientists who manage to find funding for these kinds of projects. They are forging ahead, studying creatures most people ignore, but that play critical roles in the survival of ecosystems and the people who depend upon them.