Friday, August 7, 2015

Common Water Strider

Water Striders are unique, and interesting insects that are often found skimming across the surface of the water in lakes, ponds, rivers and streams. The one pictured here is the Common Water Strider (Aquarius remigis), and is possibly the most common water strider found throughout North America, especially in the Midwest. Many people refer to them as water spiders, however they are not arachnids at all, but rather true bugs in the order Hemiptera and family Gerridae.

Have you ever visited a clear stream and noticed shadows passing across the pebbles and debris on the stream bed? Those moving shadows are often the first thing you see of these insects. Upon closer inspection you will see the insect causing those shadows as it moves across the water. Striders have specialized hairs on their legs that help them repel water, which allows them to glide (or stride) across the surface of the water. Their bodies have velvet-like hairs covering them which also repels water keeping them dry despite the fact that they live an entirely aquatic life. 

This is a fairly large species with body lengths up to 3/4 of an inch, but with their elongated legs they look much larger, nearly the size of a quarter in diameter. Their bodies are dark brown, or black and the margins are white. All the literature I read claims the adults generally lack wings, so I assume this means there are a few individuals that may be able to fly.

To find mates they will send ripples across the surface of the water that other striders will recognize as a potential partner. After mating, females will lay eggs on the rocks, logs, water plants or other items in the water. After a few weeks the eggs will hatch and the nymphs look almost identical to the adults only much smaller. After several molts they will reach adult size and sexual maturity. Once mating season is over they will often congregate in large groups all randomly moving in circles. If disturbed they will scatter and hide in cracks, crevices or other secluded areas away from danger. Birds are fond of eating water striders and will often prey on them. Given their aquatic life, you might assume fish would eat them. This however does not seem to be the case as fish rarely consume them. Maybe they give off a defensive substance that fish find distasteful.

Water striders, like many true bugs are predators and feed on other insects and spiders. They have sucking mouthparts and specialized enzymes in their saliva that aid in paralyzing and partially digesting their prey. Bugs and spiders that happen to fall into the water are quickly targeted and consumed by striders. If it is a particularly large prey item, several striders may share, like a communal meal. In the case of smaller prey items they will often fight to keep their meal or run away quickly when another strider approaches. Which is what the one pictured here did. Several other striders attempted to take her insect from her and she wasn't having it! She spent 10 minutes running from place to place to avoid other striders, before finally being able to enjoy her meal in peace. They are also known to feed on mosquito wigglers, which makes them hugely beneficial to humans. After all none of us likes mosquitoes!

Even though they are harmless to humans, a bite from one of these would be a somewhat painful experience. Like most true bugs that piercing mouthpart they use to capture and kill insects can also pierce human skin and the enzyme in their mouth can cause irritation at the bite site which might result in itching or redness. 

I can't think of much I enjoy more than sitting on the shore of a crystal clear stream, and listening to the birds singing, and feel the cool breezes blowing off the water and watching the water striders skate across the surface of the water with no particular place to go.

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