Cockroaches have been around for millions of years and can be found in many places around the world. Despite their prevalence, there remain many mysteries about these insects, including what color their blood is. In this 5000 word article, we will explore what is known about the circulatory system and blood of cockroaches to try to determine what color it is.
What is cockroach blood called?
The blood of cockroaches, like all insects, is not called blood at all. Instead, it is referred to as hemolymph or haemolymph. This name comes from the Latin words haemo, meaning blood, and lymph, meaning water. So hemolymph is essentially “blood water.”
Hemolymph is composed of plasma and does not contain red blood cells like vertebrate blood. The plasma is circulated through the interior of the cockroach’s body by a simple heart, flowing around the tissues and organs. Oxygen is delivered directly by the tracheal system rather than through hemoglobin in red blood cells.
What gives vertebrate blood its red color?
In vertebrates like mammals, the red color of blood comes from hemoglobin. Hemoglobin is a protein contained inside red blood cells that binds to oxygen, enabling its transport around the body. Hemoglobin gets its reddish hue from the presence of iron atoms.
When blood passes through the lungs, hemoglobin binds to oxygen molecules, turning bright red. This oxygenated blood then travels through arteries to tissues that need oxygen. After dropping off oxygen, hemoglobin turns dark red as it picks up carbon dioxide to carry back to the lungs. The blood turns bright red again as carbon dioxide is released and new oxygen is bound.
Why don’t insects have hemoglobin?
Insects and other invertebrates do not need transport proteins like hemoglobin in their hemolymph because they have an open circulatory system. Instead of their blood being contained in a closed network of veins and arteries, the hemolymph bathes the internal tissues directly.
Without cell-containing blood, oxygen simply diffuses into insect tissues from openings in their exoskeleton called spiracles. These openings connect to a network of tracheal tubes that branch throughout the body, allowing oxygen to reach cells directly without a circulatory system carrying hemoglobin.
What gives insect hemolymph its color?
Since hemolymph does not contain respiratory proteins, insects do not have the red blood coloration of vertebrate blood. Instead, the color comes from other molecules present in the plasma.
One important plasma component is hemocyanin. Like hemoglobin, hemocyanin is a protein that can bind to oxygen, but it contains copper rather than iron atoms. Hemocyanin is found in the hemolymph of many arthropods and mollusks.
Rather than being red, hemocyanin has a blue color when oxygenated. This accounts for the blue color of hemolymph in some insects and other invertebrates. However, not all insects have hemocyanin in their plasma.
Other hemolymph pigments
In insects without respiratory proteins like hemocyanin, other molecules contribute color. These include:
- Melanin – brown/black pigment
- Carotenoids – yellow/orange pigments
- Porphyrins – red pigments
The predominant plasma pigment determines the final color of hemolymph in different insect species. For example, hemolymph is yellowish in locusts and aphids due to carotenoids.
What color is cockroach hemolymph?
Cockroach hemolymph is somewhat translucent and glossy, with a yellowish tint. The yellowish color comes from carotenoid pigments dissolved in the plasma.
While the hemolymph in the main cavity of the cockroach body is a pale yellow, the color is more pronounced in some areas. The gut contains hemolymph with a bright yellow color.
Certain species may have hemolymph that appears more green than yellow. This color variation comes from differences in the type and amount of carotenoids present. Some species also possess fat body tissue that makes the hemolymph appear milky white in some areas.
Though pale, the yellowish color of cockroach hemolymph serves an important purpose. Carotenoids help boost the insect’s immune system to fight disease and infection. They also act as antioxidants to reduce damage from oxidation.
How does cockroach circulation work?
Cockroaches have an open circulatory system like all insects. Hemolymph is propelled through the interior of the body by the heart, flowing around the tissues and organs.
The cockroach heart runs along the top of the insect from head to abdomen. Rather than pumping blood like a vertebrate heart, it moves hemolymph with rhythmic contractions of valve-lined chambers. The pumping action moves the hemolymph through an open cavity called a hemocoel.
Since the cockroach heart is a long tube, rather than a centralized organ, hemolymph can flow forwards or backwards. This allows flexibility in circulation. Valves along the heart chambers keep the hemolymph flowing in the right direction.
From the body cavity, hemolymph enters spaces between cells and bathes tissues directly. It acts as a “blood” system, lymph system and interstitial fluid all in one. After delivering nutrients and oxygen, it diffuses back into the hemocoel to continue circulating.
Cockroach circulation system
Here are the key parts of the cockroach circulatory system:
- Heart – Long tubular heart pumps hemolymph through valves in chambers
- Hemocoel – Body cavity filled with circulating hemolymph
- Sinuses – Hemolymph-filled spaces around tissues
- Tracheae – Network of tubes that deliver oxygen directly to tissues
Do cockroaches bleed like humans?
When a cockroach is cut or injured, hemolymph will leak from the wound, which could be described as bleeding. However, there are important differences from human bleeding.
First, since hemolymph is composed of plasma rather than blood cells, cockroach blood appears watery instead of thick. It flows rapidly from even a small wound with low viscosity.
The hemolymph does not clot either. Humans and other vertebrates have blood clotting factors like platelets and fibrinogen that quickly form clots to plug wounds. Lacking these clotting elements, cockroach hemolymph flows freely.
While cockroaches cannot truly bleed to death, they can suffer severe hemolymph loss from injury leading to dehydration, organ failure, and eventual death. Their circulation does not form hard clots but wound sealing is aided by quickly secreted scab-like covering.
Do cockroaches have different blood types?
Blood types refer to the classification of blood based on differing surface molecules on red blood cells. For example, the human ABO blood group system consists of types A, B, AB, and O blood.
Since cockroaches do not have red blood cells or even cells circulating in their hemolymph, they do not have distinct blood types. However, there are some similarities in the molecules coating insect hemocytes (blood cells).
Insects have glycoproteins and other molecules on the surface of hemocytes used for recognizing foreign cells. Their immune system uses them to detect invading microorganisms and parasites. So while not exactly blood types, cockroaches have specialized hemocyte surface molecules.
Do cockroaches have white blood cells?
White blood cells, also called leukocytes, are produced in human bone marrow and circulate in the blood. They defend the body against infection through phagocytosis, releasing antibodies, and other immune functions.
Cockroaches do not have true white blood cells. However, they do have hemocytes that migrate through the hemolymph and serve similar protective roles as human white blood cells:
- Granulocytes – Phagocytose pathogens and release enzymes to break them down.
- Oenocytoids – Produce phenoloxidase enzymes involved in melanization immune responses.
- Prohemocytes – Immature cells that can differentiate into other hemocyte types.
- Plasmatocytes – Involved in wound healing through hemolymph clotting.
So while cockroaches lack true leukocytes, they have a variety of hemocytes that circulate through the hemolymph and provide cellular immunity against infection like white blood cells.
Do cockroaches get sick from human germs?
Cockroaches have lived alongside humans for thousands of years and are remarkably adept at surviving in our homes. Their hardiness means they can withstand some exposure to pathogens and toxins that make humans sick.
Some reasons cockroaches tolerate human germs well:
- Robust immune system with pathogen-fighting hemocytes
- Resistance to radiation allows surviving contaminated environments
- Ability to develop antibiotic resistance
- Thick protective exoskeleton prevents easy infection
- Detoxification enzymes break down toxins
However, cockroaches can still become infected by certain human pathogens. For example, they can transmit bacterial diseases like salmonella and viruses like polio from contaminated environments.
While adapted to handle some of our germs, sharing living space with humans exposes cockroaches to high levels of microbes. This allows diseases to occasionally spread between humans and cockroaches.
Can cockroaches spread human diseases?
Although fairly resistant, cockroaches can both catch diseases from humans and spread them. Their habit of living and feeding in unsanitary areas allows them to transmit pathogens through contact or contamination.
Some diseases cockroaches are known to spread:
- Salmonella – Food poisoning bacteria transmitted through contamination.
- Dysentery – Severe diarrhea caused by bacteria like Shigella.
- Cholera – Severe watery diarrhea with dehydration risk.
- Typhoid Fever – Systemic illness caused by Salmonella typhi bacteria.
- Polio – Debilitating and sometimes fatal viral disease largely eradicated in humans.
Their ability to spread disease makes controlling cockroach populations important in public health efforts, food service, and households.
How do cockroaches survive severe injuries?
In addition to tolerating toxins and microbes, cockroaches have an incredible ability to live through physical injuries that would kill most insects. Even after severe wounds, cockroaches can survive losing limbs, organs, or even their head!
Here are some reasons for their resilience:
- Open circulatory system allows hemolymph loss without bleeding to death.
- Slowed metabolism allows surviving for weeks without food.
- Surgically precise self-amputation of damaged limbs.
- Decentralized nervous system so brain isn’t essential for survival.
- Powerful antibiotics in hemolymph prevent infections.
- Can regenerate lost limbs after molting.
Additionally, a cockroach will enter a comatose state after major injury to conserve energy for healing. This suspended animation helps it recover from damaging wounds.
What happens when a cockroach loses a limb?
Cockroaches can lose limbs through injury, self-amputation, or autotomy – a defensive detachment of a body part. Lost legs, antennae, and mouthparts can all be regenerated later after molting.
When a leg is severed, muscles in the surrounding area contract to pinch off the hemolymph vessels. This causes the wound to heal quickly as bleeding is minimized. Though bleeding is limited, the open wound leaves the cockroach vulnerable to desiccation and infection.
To regenerate the limb later, a special blastema structure forms under the existing exoskeleton. After molting, the blastema rapidly develops into a new, fully-formed replacement limb.
Until regenerated, the cockroach has decreased mobility from the missing leg. However, its other legs adapt to allow ambulation, though at a slower pace. Young cockroaches regenerate limbs more quickly than older adults.
Leg regeneration in cockroaches
Steps cockroaches take after losing a leg:
- Severed leg is quickly detached as vessels contract.
- Blastema structure forms under exoskeleton near wound.
- During molting, blastema rapidly develops into new leg.
- Cockroach ambulates on remaining legs until regenerated.
How does cockroach hemolymph compare to human blood?
While cockroach hemolymph and human blood have some similarities in function, their composition and characteristics differ significantly:
| Feature | Cockroach Hemolymph | Human Blood |
|---|---|---|
| Main components | Plasma | Plasma and blood cells |
| Color | Yellowish to greenish | Scarlet red |
| Circulatory system | Open | Closed |
| Transports oxygen | No – tracheal system instead | Yes – via hemoglobin |
| Clotting factors | None | Platelets, fibrinogen, others |
While cockroach hemolymph and human blood share some broad functions, their composition and characteristics are quite different given the over 500 million years separating their evolution.
Conclusion
Cockroach hemolymph is pale yellow, greenish, or milky white in color instead of the familiar red of human blood. This comes from the plasma pigments like carotenoids instead of iron-based hemoglobin in red blood cells.
Hemolymph flows through an open circulatory system propelled by a tubular heart. It delivers nutrients while oxygen reaches tissues directly through tracheae. Lacking blood cells and clotting factors, cockroaches cannot truly bleed out but can suffer dehydration from hemolymph loss.
While adapted to tolerate some toxins and pathogens, cockroaches can spread diseases from contaminated environments. Their hemocytes provide immune protection similar to human white blood cells. Even after serious wounds, cockroaches can survive the injury and regenerate lost limbs after molting.
Studying the unusual hemolymph of cockroaches provides insight into insect anatomy and resilience. Understanding how these ubiquitous insects function and interact with human society gives us ideas for controlling populations, preventing disease spread, and even designing new biomechanical systems.
