Stream Ruby: Jewel of Forest Streams

With its dazzling colours and fascinating behaviours, this little insect is a highlight for any naturalist exploring a forest stream. The stream ruby (Heliocypha bisignata), a species of damselfly, has a way of grabbing your attention — whether you are an insect enthusiast or just someone who enjoys nature.

I understand that not everyone is captivated by dragonflies and damselflies. Just because they are my study organisms, I cannot expect the same level of enthusiasm from everyone. However, that is precisely why I write about them — to bring these lesser-known creatures into the spotlight. Nature lovers visiting forests tend to focus on the larger, more charismatic species. Regal tigers, majestic elephants, and vibrant birds usually take centre stage. Even smaller mammals and reptiles have their admirers. But insects? They still fascinate only a few. Among odonates, the stream ruby is an exception. Anyone walking along a forest stream of the Western Ghats cannot ignore it. It acts as a beacon, drawing attention to the mesmerising world of dragonflies and damselflies. Once you notice a stream ruby, you will likely start noticing its relatives, too.

Despite its small size — under 4 centimetres in length — the stream ruby is a striking insect. It is usually found near shaded banks of forest streams with clear, flowing water and dense vegetation. It prefers such habitats because it needs both open spaces for flight and perches from which to hunt. This damselfly is a predator, feeding on tiny flying insects hovering near the stream’s surface. But while it is an efficient hunter, it is also prey for birds, spiders, and larger dragonflies. The stream ruby is not limited to the Western Ghats, where it is abundant. It also occurs in parts of the Eastern Ghats and Central India, wherever suitable habitats exist. However, finding one outside a natural forest stream is rare — it does not thrive in human-made waterbodies such as irrigation canals or stagnant wetlands.

The male stream ruby is a visual delight. Its thorax is a psychedelic mix of red, yellow, and black, contrasting against the black abdomen, which has only faint yellow traces. Its legs, black on the outside and white on the inside, serve an important function during courtship — displaying health and vigour to potential mates. But the most spectacular feature of the male is its wings. The wings are light brown with dark tips, but under the right light, flashes of pink and violet shimmer across their surface. These iridescent hues are not produced by pigments but by microscopic structures on the wing surface that reflect and scatter light. In contrast, the female is bulkier and lacks the bright colours of the male. Her body is mostly black with yellow markings, a more subdued appearance suited for her role in the life cycle. However, despite her less flashy looks, she is the reason the males engage in their dazzling displays and fierce territorial battles.

Although small, stream ruby males are highly territorial. You rarely find two males perched close together without an aerial battle breaking out. Their fights are spectacular — fierce yet elegant displays of speed, agility, and colour. Males defend tiny stretches of prime streamside real estate. The best territories have an optimal water flow, plenty of floating debris for egg-laying, and enough sunlight filtering through the canopy. When another male intrudes, a dogfight ensues. The resident male takes off, flaring his iridescent wings to intimidate the challenger. If the rival does not back down, the two engage in mid-air sparring matches, twisting and turning with breathtaking precision. These battles are usually short but intense. The stronger male ultimately drives the other away, ensuring that he alone holds the prime location for attracting females. But territory is only one piece of the puzzle. Once a male secures his space, he must still convince a female to mate with him.

Attracted by the presence of good egg-laying sites, a female stream ruby enters a male’s territory. The resident male, eager to impress, begins the courtship display. He hovers before her, flashing the white underside of his legs — a sign of his fitness and health. If the female is interested, she allows him to mate with her. Damselfly mating is a complex process involving the famous “wheel position”, where the male clasps the female behind her head while she curves her abdomen to receive his sperm. Once mating is complete, the female searches for a suitable place to lay her eggs. Unlike most damselflies that lay eggs on the soft tissues of water plants, the stream ruby chooses floating debris, often wet, partially submerged wood. She uses her sharp ovipositor (needle-like organ) to pierce the wood and deposit her eggs inside, protecting them from predators and ensuring they stay moist. 

Once the eggs hatch, the larvae (nymphs) begin their aquatic phase. These young damselflies are voracious hunters, feeding on small aquatic invertebrates. They breathe through gill-like structures at the end of their abdomen and remain hidden among submerged vegetation or debris. Depending on environmental conditions, they may spend several months to a year in this stage, undergoing multiple moults as they grow. When ready for their final transformation, they crawl onto rocks or stems near the water’s edge. There, they shed their larval skin in one final moult, emerging as the dazzling adults we admire. From a water-dwelling predator to a swift-flying insect, this dramatic transformation is one of nature’s most fascinating processes.

The stream ruby is more than a beautiful insect. Its presence is an indicator of habitat health. Since its larvae require clean, oxygen-rich water and its adults prefer shaded, undisturbed streams, finding a population of stream rubies suggests that the local ecosystem is intact. However, these habitats are increasingly threatened by deforestation, pollution, and water diversion projects. Streams once rich in life are turning into dry beds or polluted drains, making it difficult for species like the stream ruby to survive. By paying attention to these small creatures, we can gain valuable insights into the health of our freshwater ecosystems.

If you ever find yourself near a forest stream, pause for a moment and observe. Look for a tiny insect flashing red, yellow, and black, hovering just above the water’s surface. If you spot a stream ruby, watch its behaviour — perhaps you will see a territorial skirmish, a courtship display, or a female carefully selecting a spot to lay her eggs. And who knows? This little insect might spark your interest in the hidden world of odonates. After all, nature’s jewels aren’t always the biggest or the most famous — sometimes, they are just a few centimetres long, flitting over a stream in a quiet corner of the forest.