OLDEST

Moniezia expansa

A portion of a tapeworm on a small glass slide is the oldest specimen in the collection. It dates to before 1810 and was brought to the United States by the collection’s first curator, Charles Wardell Stiles. The rest of the worm, which was found in the innards of a Dorcas gazelle, is at the Museum fur Naturkunde in Berlin.

MOST LOYAL

Schistosoma mansoni

Female

Male

You may not normally think of parasites as monogamous, but this female worm tucks into a groove in the male and the two become attached for life. Despite that awww-inspiring quirk, these blood flukes are devastating to humans. They cause schistosomiasis (also called bilharzia), a disease that spreads through contaminated water and can damage the bladder, kidneys and liver. More than 61 million people were treated for it in 2014, according to the World Health Organization.

LEAST LIKELY TO LET GO

Branchotenthes robinoverstreeti

This blood-sucking fluke hangs onto the gills of shark rays. The end that attaches has muscular, squid-worthy suckers and hooks. It was named after prominent parasitologist Robin Overstreet (but looks nothing like him).

BEST NAME

Seussapex karybares

The Worm in the Hat? Parasitologists chose “Seussapex” because they thought one end of this tapeworm looked like something Dr. Seuss would’ve drawn, right down to the ski hat with the ball on top. (Unfortunately, the ski hat part didn’t make it into the species’ official description.)

TASTIEST LOOKING

(IF YOU’RE A BASS)

Proterometra ariasae

An unsuspecting bass is swimming along in a stream and feeling peckish. It sees a wiggly bug larva and sucks it down — except it isn’t a bug, but a juvenile stage of this worm. This trematode, or fluke, then infects the mouth cavities of the poor bass that was fooled into eating it.

A portion of a tapeworm on a small glass slide is the oldest specimen in the collection. It dates to before 1810 and was brought to the United States by the collection’s first curator, Charles Wardell Stiles. The rest of the worm, which was found in the innards of a Dorcas gazelle, is at the Museum fur Naturkunde in Berlin.

OLDEST

Moniezia expansa

You may not normally think of parasites as monogamous, but this female worm tucks into a groove in the male and the two become attached for life. Despite that awww-inspiring quirk, these blood flukes are devastating to humans. They cause schistosomiasis (also called bilharzia), a disease that spreads through contaminated water and can damage the bladder, kidneys and liver. More than 61 million people were treated for it in 2014, according to the World Health Organization.

MOST LOYAL

Schistosoma mansoni

Female

Male

This blood-sucking fluke hangs onto the gills of shark rays. The end that attaches has muscular, squid-worthy suckers and hooks. It was named after prominent parasitologist Robin Overstreet (but looks nothing

like him).

LEAST LIKELY TO LET GO

Branchotenthes

robinoverstreeti

The Worm in the Hat? Parasitologists chose “Seussapex” because they thought one end of this tapeworm looked like something Dr. Seuss would’ve drawn, right down to the ski hat with the ball on top. (Unfortunately, the ski hat part didn’t make it into the species’ official description.)

BEST NAME

Seussapex karybares

An unsuspecting bass is swimming along in a stream and feeling peckish. It sees a wiggly bug larva and sucks it down — except it isn’t a bug, but a juvenile stage of this worm. This trematode, or fluke, then infects the mouth cavities of the poor bass that was fooled into eating it.

TASTIEST LOOKING

(IF YOU’RE A BASS)

Proterometra ariasae

OLDEST

Moniezia expansa

A portion of a tapeworm on a small glass slide is the oldest specimen in the collection. It dates to before 1810 and was brought to the United States by the collection’s first curator, Charles Wardell Stiles. The rest of the worm, which was found in the innards of a Dorcas gazelle, is at the Museum fur Naturkunde in Berlin.

Male

Female

MOST LOYAL

Schistosoma mansoni

You may not normally think of parasites as monogamous, but this female worm tucks into a groove in the male and the two become attached for life. Despite that awww-inspiring quirk, these blood flukes are devastating to humans. They cause schistosomiasis (also called bilharzia), a disease that spreads through contaminated water and can damage the bladder, kidneys and liver. More than 61 million people were treated for it in 2014, according to the World Health Organization.

LEAST LIKELY TO LET GO

Branchotenthes

robinoverstreeti

This blood-sucking fluke hangs onto the gills of shark rays. The end that attaches has muscular, squid-worthy suckers and hooks. It was named after prominent parasitologist Robin Overstreet (but looks nothing like him).

BEST NAME

Seussapex karybares

The Worm in the Hat? Parasitologists chose “Seussapex” because they thought one end of this tapeworm looked like something Dr. Seuss would’ve drawn, right down to the ski hat with the ball on top. (Unfortunately, the ski hat part didn’t make it into the species’ official description.)

TASTIEST LOOKING (IF YOU’RE A BASS)

Proterometra ariasae

An unsuspecting bass is swimming along in a stream and feeling peckish. It sees a wiggly bug larva and sucks it down — except it isn’t a bug, but a juvenile stage of this worm. This trematode, or fluke, then infects the mouth cavities of the poor bass that was fooled into eating it.

MOST ABUNDANT

Toxoplasma gondii

CDC Public Health Image Library

Some picky parasites live only in certain species, but this protozoan will infect just about any warm-blooded animal. People who have spent time with cats often have it in their bodies. Toxoplasmosis can cause flu-like symptoms but poses little threat to most people. However, it can cause serious problems in people with weak immune systems and can cause birth defects if a pregnant woman acquires it.

DEADLIEST

Plasmodium falciparum

CDC Public Health Image Library

This mosquito-borne parasite causes the most deadly type of malaria, which killed 438,000 people in 2015, according to the WHO’s estimate. This creature is the reason travelers to some regions need to take anti-malarial drugs. It multiplies rapidly in the blood and can cause high fever, anemia and clogged blood vessels.

BEST DISGUISE

Porocephalus

Alejandro Oceguera Figueroa (UNAM)

Pentastomids are called tongue worms because they look like worms (and tongues), but they are actually crustaceans, almost like mini crabs that have adapted to the parasitic lifestyle. (The one in the image, a Porocephalus species, came from the lungs of a green rat snake.) Phillips said she loves the surprise in finding an animal that appears to be one thing but is actually something completely different.

SMALLEST

Early stage of Leishmania

National Institute of Health

Even if it were on display, you couldn’t see the museum’s tiniest specimen without a microscope. It is a very early life stage of the Leishmania species, just

2.5 to 5 microns in length. (There are 25,400 microns in an inch.) Humans get this parasite from sand fly bites, and it creates nasty skin lesions. One type of Leishmania causes lesions on internal organs and can be deadly.

MOST LIKELY TO STAR IN A ZOMBIE FLICK

Nematomorpha

Anna J. Phillips (NMNH, Smithsonian)

Juvenile horsehair worms (or hairworms) infect arthropods, such as crickets and roaches. Once a worm matures inside, it temporarily takes over the host’s brain — or at least its behavior — and compels the insect to fling itself into fresh water. There, the worm emerges from the insect’s cloaca (rear end), and both worm and host go their separate ways.

LONGEST

Diphyllobothrium latum

If you saw this jar on a deli shelf, you’d probably assume it was full of sauerkraut, or maybe cooked egg noodles. You would be wrong. It contains just five tapeworms, suspended in alcohol, each 26 to almost 33 feet long. Phillips pulled these broad fish tapeworms out of the intestines of a stranded bottlenose dolphin in 2014. Even more unnerving, Diphylobothrium latum is one of the three species of tapeworms that humans can get. We acquire it by eating undercooked fish.

BEST PRESENTATION

Nematobibothrioides histoidii

Sometimes, very long specimens are cut into smaller pieces and prepared on a series of slides. But this nearly 16-foot-long worm was kept intact and arranged on a single large glass plate almost 50 years ago. At a glance, it looks like a tapeworm, but it is an unusually shaped fluke that came from a California sunfish in 1967.

MOST ABUNDANT

DEADLIEST

Toxoplasma gondii

Plasmodium falciparum

CDC Public Health Image Library

CDC Public Health Image Library

Some picky parasites live only in certain species, but this protozoan will infect just about any warm-blooded animal. People who have spent time with cats often have it in their bodies. Toxoplasmosis can cause flu-like symptoms but poses little threat to most people. However, it can cause serious problems in people with weak immune systems and can cause birth defects if a pregnant woman acquires it.

This mosquito-borne parasite causes the most deadly type of malaria, which killed 438,000 people in 2015, according to the WHO’s estimate. This creature is the reason travelers to some regions need to take anti-malarial drugs. It multiplies rapidly in the blood and can cause high fever, anemia and clogged blood vessels.

BEST DISGUISE

SMALLEST

Porocephalus

Early stage of Leishmania

Alejandro Oceguera Figueroa (UNAM)

National Institute of Health

Pentastomids are called tongue worms because they look like worms (and tongues), but they are actually crustaceans, almost like mini crabs that have adapted to the parasitic lifestyle. (The one in the image, a Porocephalus species, came from the lungs of a green rat snake.) Phillips said she loves the surprise in finding an animal that appears to be one thing but is actually something completely different.

Even if it were on display, you couldn’t see the museum’s tiniest specimen without a microscope. It is a very early life stage of the Leishmania species, just

2.5 to 5 microns in length. (There are 25,400 microns in an inch.) Humans get this parasite from sand fly bites, and it creates nasty skin lesions. One type of Leishmania causes lesions on internal organs and can be deadly.

LONGEST

Diphyllobothrium latum

If you saw this jar on a deli shelf, you’d probably assume it was full of sauerkraut, or maybe cooked egg noodles. You would be wrong. It contains just five tapeworms, suspended in alcohol, each 26 to almost 33 feet long. Phillips pulled these broad fish tapeworms out of the intestines of a stranded bottlenose dolphin in 2014. Even more unnerving, Diphylobothrium latum is one of the three species of tapeworms that humans can get. We acquire it by eating undercooked fish.

MOST LIKELY TO STAR IN A ZOMBIE FLICK

Nematomorpha

Juvenile horsehair worms (or hairworms) infect arthropods, such as crickets and roaches. Once a worm matures inside, it temporarily takes over the host’s brain — or at least its behavior — and compels the insect to fling itself into fresh water. There, the worm emerges from the insect’s cloaca (rear end), and both worm and host go their separate ways.

Anna J. Phillips (NMNH, Smithsonian)

BEST PRESENTATION

Nematobibothrioides histoidii

Sometimes, very long specimens are cut into smaller pieces and prepared on a series of slides. But this nearly 16-foot-long worm was kept intact and arranged on a single large glass plate almost 50 years ago. At a glance, it looks like a tapeworm, but it is an unusually shaped fluke that came from a California sunfish in 1967.

MOST ABUNDANT

DEADLIEST

BEST DISGUISE

Toxoplasma gondii

Plasmodium falciparum

Porocephalus

CDC Public Health Image Library

CDC Public Health Image Library

Alejandro Oceguera Figueroa (UNAM)

Some picky parasites live only in certain species, but this protozoan will infect just about any warm-blooded animal. People who have spent time with cats often have it in their bodies. Toxoplasmosis can cause flu-like symptoms but poses little threat to most people. However, it can cause serious problems in people with weak immune systems and can cause birth defects if a pregnant woman acquires it.

This mosquito-borne parasite causes the most deadly type of malaria, which killed 438,000 people in 2015, according to the WHO’s estimate. This creature is the reason travelers to some regions need to take anti-malarial drugs. It multiplies rapidly in the blood and can cause high fever, anemia and clogged blood vessels.

Pentastomids are called tongue worms because they look like worms (and tongues), but they are actually

crustaceans, almost like mini crabs that have adapted to the parasitic lifestyle. (The one in the image, a Porocephalus species, came from the lungs of a green rat snake.) Phillips said she loves the surprise in finding an animal that appears to be one thing but is actually something completely different.

LONGEST

Diphyllobothrium latum

SMALLEST

MOST LIKELY TO STAR IN A ZOMBIE FLICK

Early stage of Leishmania

Nematomorpha

National Institute of Health

Anna J. Phillips (NMNH, Smithsonian)

Even if it were on display, you couldn’t see the museum’s tiniest specimen without a microscope. It is a very early life stage of the Leishmania species, just

2.5 to 5 microns in length. (There are 25,400 microns in an inch.) Humans get this parasite from sand fly bites, and it creates nasty skin lesions. One type of Leishmania causes lesions on internal organs and can be deadly.

If you saw this jar on a deli shelf, you’d probably assume it was full of sauerkraut, or maybe cooked egg noodles. You would be wrong. It contains just five tapeworms, suspended in alcohol, each 26 to almost 33 feet long. Phillips pulled these broad fish tapeworms out of the intestines of a stranded bottlenose dolphin in 2014. Even more unnerving, Diphylobothrium latum is one of the three species of tapeworms that humans can get. We acquire it by eating undercooked fish.

Juvenile horsehair worms (or hairworms) infect arthropods, such as crickets and roaches. Once a worm matures inside, it temporarily takes over the host’s brain — or at least its behavior — and compels the insect to fling itself into fresh water. There, the worm emerges from the insect’s cloaca (rear end), and both worm and host go their separate ways.

BEST PRESENTATION

Nematobibothrioides histoidii

Sometimes, very long specimens are cut into smaller pieces and prepared on a series of slides. But this nearly 16-foot-long worm was kept intact and arranged on a single large glass plate almost 50 years ago. At a glance, it looks like a tapeworm, but it is an unusually shaped fluke that came from a California sunfish in 1967.

SOURCE: Kirsten Jensen, University of Kansas; Erik S. Loker, University of New Mexico; Steven A. Bullard, Auburn University; Centers for Disease Control and Prevention; WHO World Malaria Report 2015; Mayo Clinic. Note: Colors and sizes are diagrammatic..