Species: Plecia nearctica Hardy, 1940

I named this blog Lovebug because I love bugs. I also have an early memory of being amazed by a huge cloud of lovebugs surrounding me in my backyard. Maybe that's where I first began my fascination with insects. You're probably familiar with lovebugs if you live in the American Southeast. They’re the little black and red flies that descend upon the world and stick to your car. Like me, you might have assumed that the summer swarms were always a part of the landscape. Lovebugs are actually native to Mexico and Central America, and they only made it to the US in the 1920s. That makes them a very recent invasion, biologically speaking. Their northward expansion was a natural migration and not the result of human introduction, intended or accidental. Some authors still refer to them as "invaders" because of their relatively new arrival to North America, but they should not be mistaken for a human-introduced species.

bob in swamp

Lovebugs can certainly be annoying en masse, but I find them endearing (in fairness I find most bugs endearing). They aren't very good fliers, especially when coupled. They fly slowly, they bump into things, and they’re very easy to catch. They have a hard time walking on surfaces because the male and female tend to have different ideas about which way to move. They don't bite or sting, so they can't hurt you at all. The one big downside is that they will stick to your car in large numbers and can actually cause damage to the paint if you don't scrape them off quickly. So if you're new to the South, watch out.

MyFWC Florida Fish and Wildlife

Origin

There is apparently a persistent and long-standing rumor that lovebugs were "created" by the University of Florida to eat mosquitos. I can’t help but love this idea that some mad scientists at my alma mater fabricated an entire species from nothing and released it unto the world, to wreak havoc on highways. Unfortunately, it’s impossible. Not to mention the fact that a lovebug doesn’t have the mouthparts to eat another insect, much less a mosquito nearly its own size. Sadly, it seems lovebugs evolved the good old fashioned way. The genus Plecia has around 75 extant species, and 113 extinct ones. That means there's a long and robust fossil record to support our lovebug's evolution. Most of the living species (that I could find pictures of) look very similar to each other, with the characteristic black body and red thorax.

Reproductive Strategy

Lovebugs get their common name from their, uh, active love life. Insect life cycles are usually brief: the egg hatches, the larva eats enough to pupate, the adult emerges from the pupa, the adult finds a mate, the next generation is produced. Lovebugs only live as adults for less than a week, so mating is the only priority. During mating, the male and female flies become attached at the abdomen. It takes about 12 hours to complete the sperm transfer, but the bugs will stay attached for up to 2 days. Why? It's an adaptation to increase the male's chances of producing offspring. If the male stays attached, he prevents any other males from mating with his female. This way the female's entire clutch of eggs will be fathered by him, instead of split between different males.

Now, the downside to this strategy is that the male does not get to mate with other females, which would be another way of increasing his chances of having offspring. So we have a classic evolutionary trade off--mate with only one female but ensure reproduction, or mate with many females with no guarantees. This is the same tradeoff seen in other monogamous vs polygamous animals, so I would consider lovebugs a form of insect monogamy. Both strategies have been successful on Earth, but a surprising number of creatures have evolved to be monogamous or serially monogamous (only one partner until the partner dies).

Lovebugs may be the best example of extended sexual coupling, but they are not the only insects that do this. Even other animals like dogs and wolves stay locked together after mating, although it lasts minutes instead of days.

The male lovebug will actually die attached to the female, and she has to drag his corpse around while she finds a good spot to lay her eggs--up to 350 of them. Multiply that by the number of females that survive to lay eggs, and that's an awful lot of bugs. Lovebugs are a great example of R strategists. R and K selection theory is the idea that there is a trade-off between number of offspring and likelihood of survival. R-selected species make many many babies, but most will die before adulthood (ex: frogs). K-selected species only produce a few offspring, but each one is cared for to maximize its chances for survival (ex: humans and other apes). Like most theories, it's a bit of an oversimplification and can't be applied easily to all organisms.

Lovebug populations explode in April/May and August/September to coincide with spring and fall rains. The swarms last about a month each time. The flies are still around the rest of the year, just in much lower numbers.

Classification

Lovebugs are true flies in the order Diptera. They may not look like the average fly that comes to mind, which is probably a house fly (Muscidae) or similar family. Luckily, flies are easily distinguished from other orders because they only have 2 wings (Di-ptera, two-wing). Other flying insects (don't even start with Strepsiptera, I'll get to that someday) have 4 wings, or 2 pairs. In flies, the hindwings haven't disappeared completely; they’ve been modified into halteres, which function as gyroscopes to help the insects fly better. A haltere looks like a knob on a stick. Here are some pictures:

Emily Coyte

@bisc317

If you see halteres, it's a fly. All flies have halteres. They're very easy to see on craneflies (also Nematocera) (see photos). Lovebugs have them too, but you’d have to lift the black forewings away to find them.

Flies also commonly have big round eyes that touch at the top of the head, and short stubby antennae. Lovebugs fit this picture.

The beginner entomologist is in luck because lovebugs are very easy to identify and there are only two species occurring in North America, so a species ID is possible. Many insect groups aren’t so simple, and it can be next to impossible to identify a specimen down to the exact species. People devote their entire careers to sorting out things like that.

Lovebugs are in the family Bibionidae, the march flies. Bibionidae is in the superfamily Nematocera, which is basal to Brachycera. This just means that taxonomists split flies into 2 huge groups, and Nematocera evolved first (we know from morphology and DNA). Nematocera is characterized by delicate-looking flies with long, thin legs. Bibionidae is something of an exception to that rule. I would not consider the family particularly delicate.

Mardon

Bibio sp.

BugLady

There is actually a US native lovebug in the same genus. Plecia americana is a closely related fly that looks almost identical to P. nearctica. You can tell them apart by looking at the thorax- P. nearctica is only red on the top of the thorax (dorsal side), but P. americana is red all around the thorax, on the dorsal and ventral sides.

P. americana is much more rarely seen. They don't produce massive swarms over highways the way lovebugs do, instead keeping to wooded areas. They emerge in the spring only, lacking the additional fall flight that lovebugs have. P. americana was also described by Hardy in 1940. Unlike P. nearctica, P. americana is native to North America. It seems to occur in a belt of states on the Eastern side of the country, North and South Carolina west to Missouri. 

Ecology

So why should you love lovebugs? Like all organisms, they occupy an important ecological niche that other organisms have come to rely on. Adult lovebugs feed on nectar, helping to pollinate wildflowers such as goldenrod and clover. The larvae play an important role in breaking down decomposing matter. Fungi, bacteria, and earthworms are the most well known decomposers, but many insect species also belong to this group (termites are an important example). Without decomposers, the earth would be overrun with dead material, and nutrients could never be recycled back into the food chain.

James Castner

Lovebug larvae are cryptic, caterpillar-like maggots that live in the top layer of soil. They are eaten by birds, centipedes, and insects such as earwigs and beetles. I would guess other small animals, such as frogs, probably prey on lovebugs as well, but there is limited information on the subject.

You'd expect that a giant swarm of clumsy fliers would be easy prey, but adult lovebugs have surprisingly few predators. Wikipedia says nobody likes to eat the adults because of the "acidic taste," but I can't find good evidence to support that. There has been speculation that lovebugs exhibit aposematic coloration--bold colors that warn predators of distasteful/toxic compounds. A 2009 study found that lovebugs were not toxic. However, that study had a very limited scope. It's possible that there are so many black/red distasteful insects (particularly in Florida) that predators have learned to avoid all black and red things, and thus leave the lovebugs alone. The lovebug's lack of predators remains something of a mystery.

It seems the lovebug is here to stay in the Southeast. It's possible its range will continue to expand northward as global temperatures increase. They may be hard on your car, but they're good for the soil, and they don't seem to have much impact on local wildlife communities. Swarm numbers have gone down as natural population controls like parasitic fungi catch up to the lovebugs. So even though they have few predators, they aren't running around unchecked like many invasive species.

Lovebugs get plenty of hate, so the next time you see one (or a thousand), show them a little love.