A cockroach gets crushed under someone’s heel. Lift the shoe, and what’s that splattered on the tile? Well, it’s not blood––because bugs don’t have blood. The blotch on the floor is likely a mix of the bug’s internal organs, carapace, and hemolymph, a substance that acts like blood.
Bugs don’t have circulatory systems in the same way that humans do. Instead, they have hemolymph that contains plasma, proteins, carbohydrates, lipids, and ions. It transports molecules throughout the bug’s body and helps remove waste.
Bugs Don’t Have Blood
To fully understand why bugs don’t have blood, it’s important to know how their circulatory systems work.
As humans, we have a closed circulatory system. Blood flows through a series of vessels to various parts of the body. On the other hand, bugs have open circulatory systems. Hemolymph doesn’t move through vessels, but instead, flows throughout the body and into cavities called “hemocoels.” This helps the bug’s internal organs work.
Bugs also don’t have hearts. Instead, hemolymph runs through a dorsal vessel along its back and into the head. It’s worth noting that hemolymph only goes through the dorsal vessel once. It’s not like the human body that continuously moves blood to and from the heart.
Bugs Don’t Have White Blood Cells
The human body can fight off infections thanks to its blood’s white cells. White blood cells fight off infections, viruses, and other threats. However, even though bugs don’t have white blood cells, they do have sophisticated immune systems that keep them safe.
According to Virulence, bugs have an immune system very similar to humans’, but it doesn’t employ an antibody-defense response. Instead, it uses something called “immune priming” to fight off pathogens and other deadly materials.
If a bug runs out of hemolymph, it will either struggle to survive or flat-out die. However, aside from being squashed, bugs have a hard exterior that prevents hemolymph from escaping. Without this substance, a bug can’t get much-needed nutrients and navigate the world around it.
Some Bugs Rely on Human Blood
Wait. If bugs don’t have blood, then why do some bite humans? The reason usually lies with bugs’ need to reproduce. For instance, there are a lot of proteins, iron, and other nutrients in blood that mosquitoes crave. So, to help their eggs mature, they need human blood.
According to the University of Florida, these insects also rely on human blood to reproduce and survive:
- Stable flies
- Horseflies
- Deer flies
- Sand flies
- Head and pubic lice
- Bed bugs
- Bloodsucking conenoses
- Fleas
Contrary to popular belief, the bloodsucking leech is not a bug. It’s in the worm family, not far from earthworms.
Bugs Can Transmit Bloodborne Diseases
As noted, although bugs don’t have blood, some need human blood to survive. Unfortunately, this isn’t always a fair exchange; while sucking blood, an insect may transmit a harmful disease that can lead to serious symptoms. These bugs (and their corresponding illness) include:
- Oriental rat fleas. These are the nasty little buggers that caused the plague. They can infect people by sucking their blood. Thankfully, cases of the modern-day plague are rare, only affecting a handful of people in the western United States each year.
- Mosquitos. Malaria is a serious illness that threatens anyone who remains outdoors for long periods. Mosquitos transmit this disease when they suck blood and release viruses into the host’s bloodstream.
- Ticks. When some ticks latch onto a human, they may transmit a bacteria called burgdorferi that can cause Lyme disease. Symptoms can include headaches, fatigue, joint pain, and a characteristic skin rash.
- Lice. While lice aren’t technically bugs (they’re insects), they can spread a disease called “trench fever.” This can affect immunocompromised individuals and cause weight loss, headaches, and shin pain.
Meet These Animals That Don’t Have Blood
Bugs needn’t feel bad about not having blood. These creatures are also bloodless:
- Jellyfish. According to the National Oceanic and Atmospheric Administration (NOAA), jellyfish don’t have brains, hearts, and (of course) blood. They are five percent flesh and 95 percent water.
- Starfish. There’s a reason why Patrick is SpongeBob’s dim-witted friend; starfish don’t have brains! They don’t have blood and instead rely on filtration systems that pump nutrients throughout its body.
- Coral reef. Coral is a living thing that, like everything else, must rely on circulation to get nutrients. Like the starfish, it also uses a filtration system to survive.
Crazy Facts About Other Animals’ Blood
The Animal Kingdom is jam-packed with creatures that boast their own blood variations. Here are some fun facts about animals and their circulatory systems:
- Octopuses have blue blood. Not only that, but they have three hearts! Their blood is blue because it contains copper, which gives it a blue hue. Human blood has iron, reddening it.
- Most clams (except the blood clam) have clear blood. Clams and other bivalves have blood that circulates nutrients, but it doesn’t contain the hemoglobin that makes it red.
- Horseshoe crabs have bacteria-fighting blood. For years, the medical community has used horseshoe crab blood to fight off infections and help sick people. That’s because the blood doesn’t have white blood cells. Instead, it has coagulogen, which prevents germs from spreading.
- The green-blooded skink has green blood. As the name suggests, this elusive amphibian has green blood because of a pigment known as biliverdin.
While blood comes in many colors, it serves the same purpose across many living things.
Every Living Thing Has Some Kind of Blood
Although not every organism has blood as we know it, everything needs some kind of circulation system to thrive. Whether an organism is powered by blood or water, circulation is critical to ensuring an organism gets nutrients and removes waste. While bugs don’t have blood in the human sense, they still require a similar system to operate.
