Whirligig Beetle Facts (Gyrinus sp.)

The whirligig beetle is a water beetle in the order Coleoptera and the family Gyrinidae. There are approximately 700 species of whirligig beetle. It is a cosmopolitan animal, meaning its distribution spreads to most parts of the world. However, they are not found on eastern Pacific islands such as New Zealand and Hawaii, southern South America, or Antarctica.

The name “whirligig” comes from this small beetle’s ability to spin quickly on the surface of the water, which is used as a survival strategy. Their highly efficient methods of propulsion and movement in water have been studied and used as inspiration for the development of swimming machines and robots. Whirligig beetles are fully aquatic and can’t walk well on land because their middle and hind legs are modified into a flipper-like shape. While they are generally surface-dwelling, they will dive briefly when disturbed and carry a small air bubble under the elytra (the hardened outer wings of beetles) to extend the diving period. When necessary, they can fly well to escape predators such as fish or migrate to new habitats. During the larval stage, it is a bottom pond dweller.

The adults are often found in large aggregations which are called rafts, swarms, or schools. These swarms may contain hundreds of individuals of both sexes and sometimes even multiple species. The positioning of an individual within the aggregation can be determined by a couple of factors. Individuals hovering on the outside and front of the swarm may have more access to food because there is less competition from other beetles, but are also more likely to be preyed on by other animals because they are more exposed. One experiment found that in slow water, males are more likely to take risks on the edge of the swarm in their search for food, while females prefer to conserve energy and stay protected inside the swarm.

What Do Whirligig Beetles Look Like?

Whirligig beetles have several physical features that help them thrive in the water. They have a flattened and rounded body shape, referred to as ellipsoid. Their hard armor is smooth and secretes a waxy, water-repellant layer, making it difficult for predators to grasp onto them. They’re also generally steel or bronze in color, helping them to blend into the water whether it’s sunny or cloudy. The long front legs are adapted for seizing prey and the middle and hind legs are suited for paddling through the water.

To excel at hunting on the surface, the whirligig beetle’s short and thick antennae are highly sensitive to motion, and can detect waves on the surface of only a few micrometers in size. They will also create their own surface waves to receive feedback about their environment, in the same manner as echolocation in other animals. Like other adult insects, they have a Johnston’s organ, which are sensory cells located in the second segment of the antennae for detecting motion. In the whirligig beetle, the Johnston’s organ will be strategically positioned right at the surface.

Another unique feature that whirligig beetles have for living on the surface are their compound eyes, which are divided horizontally into two parts to allow them to see both above and below water at the same time. This helps these aquatic beetles to be excellent predators and avoid becoming prey to other animals.

The larvae can grow up to 30 mm long, and have slim, cylindrical bodies. They are well adapted for life at the bottom of ponds because they have several pairs of feathered abdominal gills that pull atmospheric oxygen.

Whirligig Beetle Habitats – Where Do They Live?

The whirligig beetle has been so evolutionarily successful that it can be found on every continent except Antarctica. It prefers calm freshwater habitats such as ponds, streams, and lakes. It will also thrive in a well-oxygenated environment, due to its benthic larval stage.

In the northern ranges where still bodies of water can become frozen through, they will migrate to larger, deeper bodies of water to overwinter. They will hibernate in the mud and then return to their original location in the spring.

What Do Whirligig Beetles Eat? (Whirligig Beetle Diet)

Whirligig beetles are carnivores, or, more technically, insectivores, who feed during the day. The adult’s diet consists mostly of terrestrial insects at the surface, including dead insects that have gotten trapped in the water.  Larvae feed on smaller aquatic insects, as well as snails, worms, and mites lower in the water column.

As a defense mechanism to deter predators, it will secrete a foul-smelling milky white liquid. The scent has been compared to rotten apples. Common predators of the whirligig beetle are fish, birds, and crayfish.

Are Whirligig Beetles Dangerous or Poisonous?

Whirligig beetles are not dangerous or poisonous, and in fact are a favorite of my children to play with due to their erratic, fun-to-watch swimming patterns. They do not bite, and will simply dart away if you come close or try to catch them.

The Life Cycle of Whirligig Beetles

The beetle’s lifespan depends on its reproductive activity, as it dies soon after it mates. On average they can live 2-3 years. Mating generally begins in spring and continues into late summer. Within this time period, up to two new generations are created each year. Although its sleek body makes it difficult for predators to get a grip on it, the male’s front legs are equipped with suction cups to give it an easier hold on the female while mating.

The whirligig beetle’s life cycle involves complete metamorphosis and 4 life stages – egg, larvae, pupa, and adult. One female will lay about 20-50 eggs total. Eggs are laid in rows on submerged vegetation, and the incubation period lasts for 5-17 days. Larvae develop in the summer, spending this developmental period bottom-feeding among rocks and vegetation. They will leave the water to pupate on the shoreline or on aquatic plants, creating a pupal case out of mud and debris. Adults emerge from their pupal case after 8-10 days. This process from egg to newly-formed adult takes about 6 weeks.

How to Attract Whirligig Beetles to Ponds? Are They Beneficial?

Whirligig beetles can be very beneficial to a home aquatic setup and act as natural cleaning agents. The whirligig beetle’s feeding behavior and diet, which includes scavenging dead insects that have gotten trapped on the surface, can help keep a pond clean. They also help regulate populations of other, less desirable aquatic insects.

They are popular with some people, especially children, for their erratic and constant movement during daylight hours and make an exciting addition to ponds. They are not at all harmful to people, and will simply swim away if you come near or try to catch them.

They can be attracted by maintaining relatively clean water, with ample open areas for swimming on the surface, and some submerged aquatic vegetation. The latter is helpful for these beetles to undergo their complete life cycle. In fact, having whirligig beetles can be an indicator of healthy water quality as they are not pollution tolerant!