15 Types of Worms: Species, Facts and Photos

Various types of worms inhabit different ecosystems on the planet. These invertebrate animals, often overlooked, exhibit diverse characteristics and behaviors. They live in deep soil, freshwater, or harsh deserts, and their diet patterns vary. Read on to learn more.

Worm Classification

Worms, these slender creatures typically lacking appendages, come in many varieties. Their classification involves three primary phyla: Platyhelminthes, Nematoda, and Annelida. 

Platyhelminthes are tiny, ribbon-like animals commonly referred to as flatworms. The term came from two Greek words – platy (flat) and helminth (worm). These creatures adapt to various habitats, including land and freshwater, and can even bring parasitic diseases. 

Even though most worm infections are not harmful, verification from reliable sources like the Centers for Disease Control is essential while researching them. 

In the Nematoda phylum, we find roundworms. Reaching 25,000 species in number, these organisms are notable for their diverse habitats. Some live in farmlands, and others in the depths of aquatic habitats. They play crucial roles as decomposers and prey for crabs and snails.

In the final phylum, Annelida, come the segmented worms. Derived from the Latin root word annelus (ring), it is known for its repetitive organ structure within each section. Earthworms and leeches are widely recognized terrestrial members, with bristle worms from marine terrains. 

Given their variety and importance, it's no surprise that worms have piqued scientific interest worldwide. The following sections discuss some of the most common and unique types of worms.

Related Read: Worm Facts.

15 Types of Worm Species

Quick links to the different types of worms:

1. Tape Worms (Cestoda)

Tapeworms reside in the stomachs of vertebrates, including humans. They lack a digestive system and absorb nutrients through their skin, feeding off their host's half-digested meals. Their bodies are elongated and segmented, each acting as an egg factory. 

Moreover, tapeworms have an intricate life cycle that involves multiple hosts. The primary host provides a nurturing environment for growth and reproduction, while the secondary host serves as a nursery for the worm's larvae. Then, the worm eggs or larvae enter the secondary host through contaminated food or water, kick-starting a new life cycle.

If you don’t want to get tapeworms, do not eat raw or undercooked meat, where cysts of tapeworm larvae hide. You can either get pork tapeworm or beef tapeworm from contaminated meat.

2. Liver Flukes (Fasciola hepatica)

Liver flukes reside inside the liver of humans, sheep, and cattle. They have a complex life cycle that involves two hosts, starting with freshwater snails as the intermediate host and ending with mammals. 

For reproduction, the host expels the fluke's eggs in their feces. Afterward, they hatch in freshwater, producing a larval form called a miracidium. 

This miracidium infects a snail and undergoes morphological changes, producing cercariae released from the snail.

When ingested, the metacercariae–the fluke larvae–travel from the duodenum through the intestinal wall and the peritoneal cavity until finally reaching the liver. They feed on blood and bile.

Once the adult fluke settles in the liver's bile ducts, it can cause a severe condition that triggers abdominal pain, fever, anemia, and jaundice. 

3. Blood Flukes (Schistosoma)

Schistosoma are parasitic flatworms in the Trematoda class. They live in the blood vessels of their hosts and require two separate hosts to complete their life cycle. 

Humans are often the primary host. These types of worms lay eggs in the host's blood vessels, which the host excretes through their waste. 

The male and female blood flukes mate for life, with the males having a groove designed to accommodate their female partners. Their eggs have a sharp-edged spine that helps carve a path through the host's tissues to reach the intestines or bladder. 

Once the eggs are in freshwater, they hatch, releasing miracidia larvae. The larvae infect freshwater snails, the second host in the blood flukes' life cycle.

4. Hookworms (Ancylostomidae)

Hookworms belong to the Ancylostomidae family. These parasitic worms barely reach 1 cm long and live inside the small intestines of humans, dogs, cats, and other mammals. Their hook-like mouthparts latch onto the intestinal wall and feed on the host's blood.

Their life cycle starts when the host expels their eggs through their feces. After a time, the eggs hatch into larvae. Infested hosts acquire hookworm disease, contracted when someone steps barefoot on contaminated soil. 

People in tropical and subtropical regions, particularly with less than ideal sanitation, are more susceptible to this disease. 

If you have hookworm disease, you might feel an upset stomach, a lack of appetite, and general fatigue. Leave parasitic infections unchecked, and the condition can escalate, leading to weight loss and impairment of children's development and learning abilities.

5. Whipworms (Trichuris trichiura)

The whipworm can grow up to 30-50 mm long. Its life cycle starts with an egg swallowed unintentionally, which hatches in the small intestine. 

Then, the larvae move to the colon and grow into adult worms, staying in the host's intestines for up to five years, laying thousands of eggs daily.

Whipworms can cause diarrhea, anemia, and growth impairment, especially in children.

6. Pinworms (Enterobius vermicularis)

Pinworms are thread-like creatures that are difficult to spot because of their pale color and thin appearance. Despite their size, which is about the same length as a staple, they are America's most common worm infection, according to the CDC. They usually infest the colon and rectum but can also explore other areas. 

Their life cycle begins when female pinworms lay their eggs at the edge of the anus, causing itching. Afterward, the eggs can survive on surfaces for up to three weeks, making them highly contagious. 

They spread through feces to the mouth through direct touch or contaminated clothes, food, or objects. Moreover, humans are the only species susceptible to pinworm infection.

7. Guinea worms (Dracunculus medinensis)

The Guinea worm is a parasite in rural areas of Africa², southwest Asia, and India with scarce clean drinking water. The worm's life cycle begins as larvae in contaminated water, moving to humans through ingestion. 

Once in the host's body, the larvae mature into female worms, growing up to 2-3 feet long. After about a year, the worm causes a painful blister on the skin, typically on the lower limbs, as it exits the body. 

As the worm leaves the body, it releases thousands of larvae into the water. Water fleas drink the infested water, perpetuating the infection cycle.

Efforts to increase access to clean drinking people and educate people about how to prevent worm infections have addressed the spread of the Guinea worm.

8. Heartworms (Dirofilaria immitis)

Heartworms primarily inhabit the cardiovascular systems of animals, including dogs and cats. They can also infect other mammals. Female heartworms can grow up to 12 inches, while males are smaller. 

The life cycle of heartworms starts when a mosquito carrying heartworm larvae bites an animal, injecting the larvae into the bloodstream. Over the next six months, the larvae develop into adult worms inside the host's body. 

While feeding on the host's blood, heartworms cause coughing, fatigue, loss of appetite, weight loss, and even heart failure in severe cases.

9. Lungworms (Dictyocaulus viviparus)

The lungworm can grow up to 3 inches long and infect the lungs of cattle and other grazing animals. Lungworms exist in temperate regions worldwide, including Europe, North America, and New Zealand. 

Its life cycle begins when it lays eggs in the host's lungs. Once the host coughs up the eggs, the host swallows and expels them through their feces. 

Afterward, the eggs hatch in the soil for grazing animals to eat. The larvae then migrate through the animal's body until they reach the lungs, where they mature into adult worms. 

The presence of lungworms in the host triggers a persistent cough, difficulty breathing, and weight loss. Moreover, lungworm infections often lead to a drop in milk production for dairy cows. In young or immunocompromised animals, the effects can be even more severe and sometimes fatal.

10. Trichina Worms (Trichinella)

Trichina worms can infect both domestic swine and wild omnivores. Their transmission to humans often stems from eating undercooked meat contaminated with the parasite. 

To prevent the resulting disease, trichinellosis, it is critical to cook all meat to a safe temperature while ensuring swine are protected from potential sources of infection³.

11. Earthworms (Lumbricus terrestris)

Earthworms originated from Europe but now live worldwide. These nocturnal creatures possess male and female reproductive organs. They also feed and mate under darkness. 

These very common types of worms breathe through their skin and require a moist environment to facilitate respiration. As they dig tunnels through the earth, these creatures improve soil fertility. They break down organic matter, recycle nutrients into the soil, and aid plant growth.

Moreover, earthworms provide a meal for birds, frogs, and badgers. Despite facing various threats, these creatures can survive up to six years in the wild.

Related read: What do Worms Eat?

12. Red Wigglers (Eisenia fetida)

Red Wigglers originated from Europe and have spread around the world. Despite their size, these worms possess an insatiable appetite for organic matter. 

These reddish-purple worms can convert waste into compost. Their digestive system breaks down the organic material into castings rich in nutrients.

Moreover, these worms can survive in temperatures ranging from 40 to 80 degrees Fahrenheit, though they prefer a moist environment. 

13. Peanut Worms (Sipuncula)

Peanut Worms live in marine habitats worldwide. They have an unsegmented, bilaterally symmetrical body divided into two parts: an introvert that serves as their head and a trunk. The introvert is retractable; the worm can pull it back into the trunk using a complex network of retractor muscles.

These types of worms inhabit intertidal zones to the deep sea. They usually live in soft spots like sand or mud or inside rocks and shells. 

Moreover, these detritivores feed on organic debris and use their introvert's tentacular crown to gather food particles from the water.

14. Bristle Worms (Polychaeta)

Bristle Worms are diverse marine annelids known for their vibrant colors, shapes, and sizes. 

They have numerous rows of chitinous, hair-like bristles lining their segmented bodies, which help them move and defend themselves. 

Bristle worms have a well-structured head equipped with eyes, antennae, and sensory palps that help them navigate their surroundings and locate food. They consume various food items ranging from plankton and detritus to other tiny organisms. 

Moreover, they can adapt to different environments, from tidal zones to the deepest ocean trenches and from the chilly, lightless abyss to the blistering heat of hydrothermal vents. 

Some species of bristle worms also display bioluminescence¹, lighting up like stars scattered across the ocean floor. When threatened, some bristle worms can shed their bristles, embedding them in the predator's skin.

15. Tubeworms (Siboglinidae)

The tubeworm has a long, tube-like form and enjoys a symbiotic relationship with resident bacteria. 

Tubeworms lack a digestive system but rely on their bacterial partners to turn chemicals in the water into nutrients via chemosynthesis. This ability allows them to thrive in inhospitable environments such as hydrothermal vents and cold seep ecosystems. 

They are impressive builders and have a protective calcium carbonate casing that enables them to reach great lengths.