Merry Christmas edition of Disease of the Week. Christmas disease actually exists. It’s a form of genetic haemophilia, i.e. patients with Christmas disease have blood that does not clot very efficiently, which means they tend to bleed a lot. You need your blood to live. Turns out bedbugs also need your blood to live. Segue!
Disease has many definitions. Here’s one: a condition of the living animal or plant body or of one of its parts that impairs normal functioning and is typically manifested by distinguishing signs and symptoms (from Merriam-Webster)1. Depending on your definitions of “condition”, “normal functioning” and “symptoms”, many things that fit this definition are not traditionally considered to be diseases. This means we can pretty much write about what we want in this blog, if we wrangle it right. Keeping this in mind, I will talk to you about bedbugs this week.
Bedbugs are insect parasites that feed exclusively on the blood of many vertebrates, including humans. Insects are sometimes talked about in medical science because they can spread diseases, such as malaria, Lyme disease and dengue virus. But, these aren’t caused by the insect itself, which is what I’m going to focus on.
Bedbugs are tough little buggers. They lose very little water while breathing, on par with insects living in the desert. Even so, they can lose a third of their total body water and walk it off. This is like you bleeding out 2 litres worth of blood and then getting up to do some grocery shopping. Also, adult bedbugs can go for 2 years without feeding.
But, without blood to feed on, females do not lay eggs and hatchlings die within days. So bedbugs usually live fairly close to their hosts. In the human case, this means they’re tucked away in mattress linings, cracks in walls, suitcases, etc. About once a week, they’ll come out of their hiding spots at night to feed.
Bedbug bites can cause a wide range of reactions. Usually there is itchiness and a welt at the site, but some people do not react at all to bites. On the other side of the spectrum, there was a case reported in 1955 of anaphylaxis due to a bedbug bite that was mistaken for a blockage in the lungs. The patient ended up dying. Fortunately, this occurs very rarely. And so, this article’s quota of disease is met. (So is Jamie’s request for a disease that doesn’t start with flu-like symptoms).
So we’ve looked at survival and food – the next crucial part of life is reproduction. That’s where the bedbug’s life gets a bit strange. To understand why, we first have to explore a bug’s body.
Detour into a bug’s anatomy
Insects are pretty different to us: they have six legs; their skeletons are on the outside of their body; their spinal cords are located along its belly, rather than along their back; and, important in this case, they have an open circulatory system, which I’ll explain in a little more detail.
We have a closed circulatory system. Our blood, under usual not-stabbed conditions, stays in our blood vessels. Blood is separated from tissues by the vessel wall. Small stuff like water and sugar can go through this wall and wash over the tissues, but bigger things like cells and proteins cannot. It’s all very closed and compartmentalised. If you inject, say, a molten plastic mixture into your veins, it’s going to stay in there. Some anatomists have actually made pretty models of circulatory systems using this very method.
In an insect, however, there’s no barrier between blood and organs. It’s all the same fluid called hemolymph. Everything can reach everywhere; proteins, cells, the whole shebang.
Another thing that’s a bit strange in insects (although other animals use them as well) is the use of mating plugs. When males finish with their mating business, they can secrete a sticky glue to clog up the female’s genital tract. This helps semen to stay in the female, increasing the chance of impregnation. But more importantly, mating plugs stops any other rival male from impregnating the lucky female. However, it turns out that bedbugs have evolved a disturbing way around this.
A quicker detour into a bug’s anatomy
To mate, male bedbugs stab a hole in the female’s abdomen and ejaculate into the hole. Due to the open circulatory system, the sperm can diffuse throughout the female’s body and eventually reach the ovaries and fertilise the eggs. This has been dubbed “traumatic insemination” for obvious reasons and it is the only way bedbugs mate. Females have a perfectly functioning set of genitals, but they are only used for the laying of eggs.
Understandably, having a big leaking hole in your thorax is fairly traumatic. Some females have died due to ruptured guts after mating. The risk of infection at the open wound is also pretty high. Scientists have found that if you put a lot of bedbugs in a small area, you see that females are repeatedly mated and a quarter of the female population dies as a result of these repeated matings.
Females have not taken this sitting down. They have evolved structures called paragenitals on their abdomens. These look similar to their real genitals and help both limit the damage caused by mating and the risk of infection of the wound afterwards, which I guess is a consolation prize.
So all in all, I think you all should be thankful for what you have this Christmas because at least it isn’t a gaping stomach wound full of semen. And if it is, good on you for reading this site and supporting us, but seriously, go get that checked out.
1 This definition (strictly speaking) is both too broad and too narrow: too broad in that, for example, being punched in the face can fit in this definition, but is generally not considered a disease; too narrow in that bacteria, fungi and archaebacteria can be infected with pathogens and cause disease, not only animals and plants.