Water Scorpion Facts & Information 2021 (Nepidae)


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Water Scorpion Facts & Information Guide 2021 (Nepidae)

An adult water scorpion aquatic stick insect Nepidae
These bugs are known as water scorpions and aquatic stick insects, due to their resemblance to scorpions and stick bugs. Photo by Ihor Panas, CC BY 4.0

Water scorpions make up the insect family Nepidae, which is a family of aquatic Heteropteran insects that come from the insect order Hemiptera. There are approximately 150 different species of water scorpion found worldwide, 13 of which are found in the United States and Canada.

They are technically related to giant water bugs, both belonging to the family Nepidae, and have a somewhat similar morphology, but water scorpions and giant water bugs belong to entirely different genera and are classified separately.

These scorpion-like water bugs are pretty ubiquitous – they are found pretty much all over the world where freshwater habitat exists. Antarctica is the only continent where members of Nepidae are not found. While they live all over the world, water scorpions are pretty elusive and are not often seen by human observers.

They have been given the common name “water scorpion” due to their resemblance to the true scorpion! While these water bugs are not actually closely related to scorpions by any standard, they sure do have some semblance of one another.

The front legs of the water scorpion are used as grappling limbs, and they have a tail end that is used in a snorkel fashion; water scorpions can stick this appendage above the water surface and use it to obtain oxygen, but they cannot attack or sting with it. While the different species of Nepidae tend to vary in shape and size, they are typically dark brown or black in color and approximately 1-2 inches (25-52 millimeters) in length.

WATER SCORPION FACT SHEET
COMMON NAMES
Water scorpion, water stick insect
SCIENTIFIC FAMILY NAME
Nepidae
TYPE
Aquatic invertebrate
DIET
Carnivorous
NATIVE HABITATS
Worldwide in freshwater habitats (except Antarctica)
AVERAGE LIFE SPAN (IN WILD)
2-2.5 years
AVERAGE SIZE
25-52 millimeters (1-2 inches)
IUCN RED LIST STATUS
Least Concern

What Do Water Scorpions Look Like?

water stick insect nepidae in a hand
With over 150 species, water stick insects can vary in appearance, but are harmless to people. This image is created by user Wim Rubers at waarneming.nl, a source of nature observations in the Netherlands., CC BY 3.0

Water scorpions typically have a dark brown or black body color, and can vary in size and shape depending on species. Many species are thin, long and stick-like, while others are more stout, and round in shape! There are over 150 species of water scorpion, and each one is unique in some way. They have large front legs that are pincer-like in appearance, a flat body, and a long tail-like appendage that can resemble the rear end of a true scorpion.

Water scorpions actually have a very fascinating adaptation that allows them to breathe oxygen. Interestingly, they obtain oxygen through their scorpion-like tail! The tail acts as a siphon, and contains tubes that function similarly to a snorkeling device. It can then trap the collected oxygen against its body for impressive periods of time, until the oxygen is depleted. Then the water scorpion must revisit the surface of the water once more to restock its supply. They tend to hang out in shallower waters, so trips to the surface can be quick and easy.

Water Scorpion Habitats – Where Do They Live?

A water scorpion on a plant
As they’re poor swimmers, water scorpions prefer habitats with plants for them to cling to. Photo by James Lindsey at Ecology of Commanster, CC BY-SA 2.5

Found worldwide except for in Antarctica, water scorpions can tolerate a range of environmental conditions. They live in freshwater habitats all over the world, but within their habitat they tend to stay in the more muddy and murky areas that contain a lot of plant matter and detritus. Plant matter is an important habitat element for water scorpions because they are not great swimmers. They use plants to hold onto, and also for cover, feeding, and reproduction.

Despite the fact that they are classified as aquatic invertebrates, water scorpions are actually not great at swimming. They are rarely found out in open water, and they therefore rely on habitat elements like vegetation, logs, and rocks to thrive. When they do swim, they are rather slow and sloth-like! Observing swimming patterns and speed can be one way to distinguish a water scorpion from other types of aquatic insects.


What Do Water Scorpions Eat? (Water Scorpion Diet)

Like all other true bugs classified in the order Hemiptera, water scorpions have piercing and sucking mouthparts that they use to feed on their prey. They are commonly referred to as “voracious predators,” and they are also what we call “ambush predators.” This is because they hide out in aquatic vegetation or detritus until unsuspecting prey comes along. The water scorpion then ambushes the prey quickly and forcefully, subduing its next meal.

Water scorpions have a fairly diverse diet, and prey on a variety of food items! They are known to eat other aquatic insects, small crustaceans, small fish, and tadpoles. During an ambush, the water scorpion will notice the prey, extend its hind legs, propel itself forwards and upwards, and cling onto the prey using its front legs. Once it has a strong and secure grasp on the prey, the water scorpion will pierce it with its beak, called a “rostrum,” inject the prey full of digestive enzymes, and use its sucking mouthparts to ingest the meal.

Are Water Scorpions Dangerous or Venomous?

With a name like “water scorpion,” you may be wondering: “is it really a good idea to attract these insects to my pond?” We are all aware of the dangers posed by true scorpions, but luckily, the similarities between true scorpions and water scorpions are mostly surface-level! While water scorpions do have the potential to bite humans and cause a little bit of pain, they are not considered dangerous or harmful to people. The benefits of attracting these insects far outweigh any drawbacks! Continue reading (or skip to the last section) to learn about how they’re beneficial to ponds and other habitats.


The Life Cycle of Water Scorpions

two water scorpions Ranatra linearis mating
Mating typically occurs in April and May. Photo by Andreas Eichler, CC BY-SA 4.0

Like all other true bugs in the order Hemiptera, water scorpions undergo incomplete metamorphosis with only three life stages. They start out in the egg stage, hatch into the nymph stage, and finally mature into the adult stage by the time they are ready to reproduce.

The mating process for water scorpions typically occurs in the months of April and May. To attract a female mate, a male will perform stridulation. He will create a chirping sound that is produced when he rubs his legs against his body, similar to crickets rubbing their wings together. Once he has attracted a mate, the male water scorpion will lay diagonally across and on top of a female, and he will grab onto her thorax using his front legs. Shortly after mating has occurred, the female will deposit her eggs – she usually does this around dusk.

A mated female will actually insert her eggs into the tissues of aquatic plants to help protect them, give them oxygen (explained below), and provide an early nutrient source for them; this does not harm the plants. She will typically choose to lay the eggs in rotting plants, moss, or algal carpets. A female can lay approximately 32 eggs in one evening.

Once the eggs have been laid by the female, the male partner comes in and guards them until they hatch into nymphs. During the egg phase, the water scorpion obtains oxygen that diffuses across the egg’s membrane from the plant matter that it is in contact with. In 2-4 weeks, the eggs will hatch! Nymphs will tend to hang out in the warmer, shallower waters of their habitat. As the nymph continues to grow and develop over time, it undergoes five separate molts before it reaches the adult stage.

After a water scorpion nymph has experienced its five molts and has ceased to develop further, it is then in the third and final stage of its life cycle – the adult stage! Unlike nymphs, adult water scorpions have fully-developed wings and full-grown bodies. They are now ready to reproduce.


How to Attract Water Scorpions to Ponds – Are They Beneficial?

how to attract water scorpions to ponds
Having a variety of floating and submerged plants is a good way to help attract water stick insects to your pond.

Attracting water scorpions to your backyard pond can be a wonderful idea if you want to improve the biodiversity on your property and ripen the conditions to attract other types of wildlife! By attracting water scorpions, you will be inadvertently providing a resource that may attract a variety of species of fish, mammals, and amphibians to your pond. If you keep larger fish in your pond, they will happily feed on water scorpions and create a balanced habitat.

Water scorpions directly help ecosystems by controlling smaller insect populations, and can even feed on tadpoles and some fish fry (so do keep this in mind if you have a garden pond). In addition, they provide a very valuable food source to many fish, birds, reptiles and amphibians, and even some mammals!

Making sure that all of the necessary and unique habitat elements are present is the first step to attracting any species. Water scorpions rely on shallow water edges, with many additional elements for cover. Aquatic vegetation, downed logs, rocks, and a bottom layer of detritus are all beneficial elements for water scorpions.

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