Bloodworms are invertebrates known for their reddish color and presence in aquatic environments. The term “bloodworm” can be confusing, as it refers to different types of creatures. This article explains what bloodworms are, where they live, and their life cycles.
Understanding Bloodworms
The name “bloodworm” refers to two distinct types of invertebrates, both recognized for their red coloration. One type is the larva of non-biting midges (Chironomidae), aquatic insect larvae found in freshwater. The other group comprises marine polychaete worms, primarily Glycera species, which are segmented worms found in saltwater.
Their striking red color comes from hemoglobin, a protein similar to that found in human blood, which binds oxygen. This adaptation allows them to absorb oxygen efficiently, even in environments with low oxygen levels. Chironomid larvae are generally small, typically ranging from 0.2 to 1 inch (5 to 25 mm) in length. Marine Glycera bloodworms can be considerably larger, with some species reaching lengths of up to 14 inches (35.5 cm). Their bodies are typically slender and segmented.
Common Environments Where They Are Found
Bloodworms are found in a wide array of aquatic habitats globally. Freshwater chironomid larvae thrive in diverse freshwater bodies, common in the muddy bottoms of ponds, lakes, and slow-moving rivers. They can also be found in ditches, water pipes, or stagnant water sources. Their ability to tolerate low-oxygen conditions in these sediments is largely attributed to their hemoglobin.
Marine bloodworms (Glycera species) inhabit saltwater environments. They are typically found burrowed within marine sediments, particularly in intertidal zones and the muddy or sandy bottoms of coastal waters. These worms prefer areas rich in organic material. Like their freshwater counterparts, marine bloodworms are well-adapted to environments with limited oxygen.
The Bloodworm Life Cycle
The life cycle of the freshwater chironomid bloodworm involves four distinct stages: egg, larva, pupa, and adult midge. Adult female midges lay eggs on the water’s surface, often in gelatinous masses that sink, and these eggs typically hatch into larvae within a few days to a week. The larvae live in the sediment, constructing silk tubes where they feed and grow, progressing through several larval stages or instars. After growth, the larva transforms into a pupa, usually while still in its tube at the bottom, and this pupal stage is relatively short, lasting from a few hours to about two weeks. From the pupa, the adult midge emerges—a non-biting, mosquito-like fly that lives for only a few days to a week, primarily to mate and lay eggs, completing the cycle.
In contrast, marine bloodworms (Glycera) have a different life cycle that does not involve metamorphosis into a flying insect. Their reproduction often involves sexually mature worms transforming into a pelagic (free-swimming) epitoke stage. During this stage, they release gametes (eggs and sperm) into the water, typically in midsummer, and then die. After fertilization, eggs develop into a larval stage, sometimes a trochophore larva, which then develops into a juvenile worm resembling the adult, growing directly without a pupal stage. Most marine bloodworms mature, spawn, and die around three years of age, though some can live up to five years.